[RFC,v2] Btrfs: Subpagesize blocksize (WIP).

Commit Message

[e-mail] Dec. 18, 2012, 7:13 a.m. UTC

From: Wade Cline <[e-mail]>

v1 -> v2:
- Added Signed-off-by tag (it's kind of important).

This patch is only an RFC. My internship is ending and I was hoping
to get some feedback and incorporate any suggestions people may
have before my internship ends along with life as we know it (this
Friday).

The filesystem should mount/umount properly but tends towards the
explosive side when writes start happening. My current focus is on
checksumming issues and also an error when releasing extent buffers
when creating a large file with 'dd'... and probably any other
method. There's still a significant amount of work that needs to be
done before this should be incorporated into mainline.

A couple of notes:
    - Based off of Josef's btrfs-next branch, commit
      8d089a86e45b34d7bc534d955e9d8543609f7e42
    - C99-style comments are "meta-comments" where I'd like more
      feedback; they aren't permanent but make 'checkpatch' moan.
    - extent_buffer allocation and freeing need their code paths
      merged; they're currently in separate functions and are both
      very ugly.
    - The patch itself will eventually need to be broken down
      into smaller pieces if at all possible...

Signed-off-by: Wade Cline <[e-mail]>
---
 fs/btrfs/ctree.h            |   11 +-
 fs/btrfs/disk-io.c          |  110 +++++++--
 fs/btrfs/extent_io.c        |  632 ++++++++++++++++++++++++++++++++++++++-----
 fs/btrfs/extent_io.h        |    7 +
 fs/btrfs/file.c             |    9 +-
 fs/btrfs/free-space-cache.c |    2 +
 fs/btrfs/inode.c            |   38 ++-
 fs/btrfs/ioctl.c            |    4 +-
 8 files changed, 709 insertions(+), 104 deletions(-)

Comments

Liu Bo Dec. 18, 2012, 7:30 a.m. UTC | #1

On Mon, Dec 17, 2012 at 11:13:25PM -0800, [e-mail] wrote:
> From: Wade Cline <[e-mail]>
> 
> v1 -> v2:
> - Added Signed-off-by tag (it's kind of important).
> 
> This patch is only an RFC. My internship is ending and I was hoping
> to get some feedback and incorporate any suggestions people may
> have before my internship ends along with life as we know it (this
> Friday).
> 
> The filesystem should mount/umount properly but tends towards the
> explosive side when writes start happening. My current focus is on
> checksumming issues and also an error when releasing extent buffers
> when creating a large file with 'dd'... and probably any other
> method. There's still a significant amount of work that needs to be
> done before this should be incorporated into mainline.
> 
> A couple of notes:
>     - Based off of Josef's btrfs-next branch, commit
>       8d089a86e45b34d7bc534d955e9d8543609f7e42
>     - C99-style comments are "meta-comments" where I'd like more
>       feedback; they aren't permanent but make 'checkpatch' moan.
>     - extent_buffer allocation and freeing need their code paths
>       merged; they're currently in separate functions and are both
>       very ugly.
>     - The patch itself will eventually need to be broken down
>       into smaller pieces if at all possible...

Could you please first elaborate why we need this subpagesize stuff and
any user case in this patch's commit log?
Or Am I missing something?

thanks,
liubo

> 
> Signed-off-by: Wade Cline <[e-mail]>
> ---
>  fs/btrfs/ctree.h            |   11 +-
>  fs/btrfs/disk-io.c          |  110 +++++++--
>  fs/btrfs/extent_io.c        |  632 ++++++++++++++++++++++++++++++++++++++-----
>  fs/btrfs/extent_io.h        |    7 +
>  fs/btrfs/file.c             |    9 +-
>  fs/btrfs/free-space-cache.c |    2 +
>  fs/btrfs/inode.c            |   38 ++-
>  fs/btrfs/ioctl.c            |    4 +-
>  8 files changed, 709 insertions(+), 104 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index fbaaf20..c786a58 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1938,14 +1938,19 @@ static inline void btrfs_set_token_##name(struct extent_buffer *eb,	\
>  #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)		\
>  static inline u##bits btrfs_##name(struct extent_buffer *eb)		\
>  {									\
> -	type *p = page_address(eb->pages[0]);				\
> -	u##bits res = le##bits##_to_cpu(p->member);			\
> +	type *p;							\
> +	u##bits res;							\
> +									\
> +	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
> +	res = le##bits##_to_cpu(p->member);				\
>  	return res;							\
>  }									\
>  static inline void btrfs_set_##name(struct extent_buffer *eb,		\
>  				    u##bits val)			\
>  {									\
> -	type *p = page_address(eb->pages[0]);				\
> +	type *p;							\
> +									\
> +	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
>  	p->member = cpu_to_le##bits(val);				\
>  }
>  
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index f633af8..00b80b7 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -373,6 +373,24 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>  					       WAIT_COMPLETE,
>  					       btree_get_extent, mirror_num);
>  		if (!ret) {
> +			/*
> +			 * I think that this is bad and should be moved
> +			 * into btree_readpage_end_io_hook(), but that
> +			 * it should apply to a single block at a time.
> +			 * That may be difficult and would make the
> +			 * function name a misnomer, but mostly I hate
> +			 * the silly goto.
> +			 */
> +			if (eb->len < PAGE_SIZE &&
> +			    !extent_buffer_uptodate(eb)) {
> +				if (csum_tree_block(root, eb, 1)) {
> +					ret = -EIO;
> +					goto bad;
> +				} else {
> +					set_extent_buffer_uptodate(eb);
> +				}
> +			}
> +
>  			if (!verify_parent_transid(io_tree, eb,
>  						   parent_transid, 0))
>  				break;
> @@ -385,6 +403,7 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>  		 * there is no reason to read the other copies, they won't be
>  		 * any less wrong.
>  		 */
> +bad:
>  		if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
>  			break;
>  
> @@ -416,29 +435,55 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>   * checksum a dirty tree block before IO.  This has extra checks to make sure
>   * we only fill in the checksum field in the first page of a multi-page block
>   */
> -
> -static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
> +static int csum_dirty_buffer(struct btrfs_root *root, struct page *page,
> +			     unsigned int offset, unsigned int len)
>  {
> -	struct extent_io_tree *tree;
>  	u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
>  	u64 found_start;
>  	struct extent_buffer *eb;
>  
> -	tree = &BTRFS_I(page->mapping->host)->io_tree;
> +	if (!PageUptodate(page)) {
> +		WARN_ON(1);
> +		return 0;
> +	}
>  
>  	eb = (struct extent_buffer *)page->private;
> -	if (page != eb->pages[0])
> -		return 0;
> +	if (eb->len >= PAGE_SIZE) {
> +		if (eb->pages[0] != page)
> +			return 0;
> +	} else {
> +		start += offset;
> +		while (eb->start != start) {
> +			eb = eb->next;
> +			BUG_ON(!eb);
> +		}
> +next:
> +		if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
> +			WARN_ON(1);
> +		if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
> +			WARN_ON(1);
> +		if (eb->pages[0] != page)
> +			WARN_ON(1);
> +	}
> +
>  	found_start = btrfs_header_bytenr(eb);
>  	if (found_start != start) {
>  		WARN_ON(1);
>  		return 0;
>  	}
> -	if (!PageUptodate(page)) {
> -		WARN_ON(1);
> -		return 0;
> -	}
> +
>  	csum_tree_block(root, eb, 0);
> +
> +	if (eb->len < PAGE_SIZE) {
> +		len -= eb->len;
> +		BUG_ON(len & (eb->len - 1));
> +		if (len) {
> +			start += eb->len;
> +			eb = eb->next;
> +			goto next;
> +		}
> +	}
> +
>  	return 0;
>  }
>  
> @@ -579,6 +624,19 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>  
>  	tree = &BTRFS_I(page->mapping->host)->io_tree;
>  	eb = (struct extent_buffer *)page->private;
> +	if (eb->len < PAGE_SIZE) {
> +		/* Find the eb that tried to submit a read request. This is
> +		 * a little bit funky. */
> +		do {
> +			if (!atomic_read(&eb->io_pages))
> +				continue;
> +			if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags) ||
> +			    test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
> +				continue;
> +			break;
> +		} while ((eb = eb->next));
> +		BUG_ON(!eb);
> +	}
>  
>  	/* the pending IO might have been the only thing that kept this buffer
>  	 * in memory.  Make sure we have a ref for all this other checks
> @@ -615,8 +673,11 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>  	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb),
>  				       eb, found_level);
>  
> -	ret = csum_tree_block(root, eb, 1);
> -	if (ret) {
> +	/*
> +	 * Subpagesize blocksize checksumming is currently done in
> +	 * btree_read_extent_buffer_pages().
> +	 */
> +	if (eb->len >= PAGE_SIZE && csum_tree_block(root, eb, 1)) {
>  		ret = -EIO;
>  		goto err;
>  	}
> @@ -631,8 +692,15 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>  		ret = -EIO;
>  	}
>  
> -	if (!ret)
> +	/*
> +	 * For subpagesize blocksize, only the page needs to be set
> +	 * up-to-date; each extent_buffer is set up-to-date when it is
> +	 * checksummed.
> +	 */
> +	if (eb->len >= PAGE_SIZE)
>  		set_extent_buffer_uptodate(eb);
> +	else
> +		SetPageUptodate(eb->pages[0]);
>  err:
>  	if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
>  		clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
> @@ -828,7 +896,8 @@ static int btree_csum_one_bio(struct bio *bio)
>  	WARN_ON(bio->bi_vcnt <= 0);
>  	while (bio_index < bio->bi_vcnt) {
>  		root = BTRFS_I(bvec->bv_page->mapping->host)->root;
> -		ret = csum_dirty_buffer(root, bvec->bv_page);
> +		ret = csum_dirty_buffer(root, bvec->bv_page, bvec->bv_offset,
> +					bvec->bv_len);
>  		if (ret)
>  			break;
>  		bio_index++;
> @@ -1007,9 +1076,13 @@ static int btree_set_page_dirty(struct page *page)
>  	BUG_ON(!PagePrivate(page));
>  	eb = (struct extent_buffer *)page->private;
>  	BUG_ON(!eb);
> -	BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
> -	BUG_ON(!atomic_read(&eb->refs));
> -	btrfs_assert_tree_locked(eb);
> +	/* There doesn't seem to be a method for passing the correct eb
> +	 * to this function, so no sanity checks for subpagesize blocksize. */
> +	if (eb->len >= PAGE_SIZE) {
> +		BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
> +		BUG_ON(!atomic_read(&eb->refs));
> +		btrfs_assert_tree_locked(eb);
> +	}
>  #endif
>  	return __set_page_dirty_nobuffers(page);
>  }
> @@ -2400,11 +2473,14 @@ int open_ctree(struct super_block *sb,
>  		goto fail_sb_buffer;
>  	}
>  
> +#if 0
> +	// Hmm. How to deal wth this for subpagesize blocksize?
>  	if (sectorsize != PAGE_SIZE) {
>  		printk(KERN_WARNING "btrfs: Incompatible sector size(%lu) "
>  		       "found on %s\n", (unsigned long)sectorsize, sb->s_id);
>  		goto fail_sb_buffer;
>  	}
> +#endif
>  
>  	mutex_lock(&fs_info->chunk_mutex);
>  	ret = btrfs_read_sys_array(tree_root);
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 1b319df..c1e052e 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2519,7 +2519,7 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>  	int contig = 0;
>  	int this_compressed = bio_flags & EXTENT_BIO_COMPRESSED;
>  	int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
> -	size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);
> +	size_t bio_size = min_t(size_t, size, PAGE_CACHE_SIZE);
>  
>  	if (bio_ret && *bio_ret) {
>  		bio = *bio_ret;
> @@ -2530,8 +2530,8 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>  				sector;
>  
>  		if (prev_bio_flags != bio_flags || !contig ||
> -		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
> -		    bio_add_page(bio, page, page_size, offset) < page_size) {
> +		    merge_bio(tree, page, offset, bio_size, bio, bio_flags) ||
> +		    bio_add_page(bio, page, bio_size, offset) < bio_size) {
>  			ret = submit_one_bio(rw, bio, mirror_num,
>  					     prev_bio_flags);
>  			if (ret < 0)
> @@ -2550,7 +2550,7 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>  	if (!bio)
>  		return -ENOMEM;
>  
> -	bio_add_page(bio, page, page_size, offset);
> +	bio_add_page(bio, page, bio_size, offset);
>  	bio->bi_end_io = end_io_func;
>  	bio->bi_private = tree;
>  
> @@ -3168,14 +3168,28 @@ static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
>  	int uptodate = err == 0;
>  	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
>  	struct extent_buffer *eb;
> +	unsigned int offset;
> +	unsigned int bv_len;
> +	u64 start;
>  	int done;
>  
>  	do {
>  		struct page *page = bvec->bv_page;
> +		offset = bvec->bv_offset;
> +		bv_len = bvec->bv_len;
> +		start = ((u64)page->index << PAGE_CACHE_SHIFT) + offset;
>  
>  		bvec--;
>  		eb = (struct extent_buffer *)page->private;
>  		BUG_ON(!eb);
> +		if (eb->len < PAGE_SIZE) {
> +			while (eb->start != start) {
> +				eb = eb->next;
> +				BUG_ON(!eb);
> +			}
> +		}
> +
> +next_eb:
>  		done = atomic_dec_and_test(&eb->io_pages);
>  
>  		if (!uptodate || test_bit(EXTENT_BUFFER_IOERR, &eb->bflags)) {
> @@ -3184,12 +3198,50 @@ static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
>  			SetPageError(page);
>  		}
>  
> -		end_page_writeback(page);
> +		if (eb->len >= PAGE_SIZE) {
> +			end_page_writeback(page);
>  
> -		if (!done)
> -			continue;
> +			if (!done)
> +				continue;
>  
> -		end_extent_buffer_writeback(eb);
> +			end_extent_buffer_writeback(eb);
> +		} else {
> +			/* Sanity checks. */
> +			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
> +				WARN_ON(1);
> +
> +			/* Ensure I/O page count is zero. */
> +			if (!done)
> +				WARN_ON(1);
> +
> +			/* Clear the extent buffer's writeback flag. */
> +			end_extent_buffer_writeback(eb);
> +
> +			/*
> +			 * See if any other extent buffers exists within the
> +			 * page.
> +			 */
> +			bv_len -= eb->len;
> +			BUG_ON(bv_len & (eb->len - 1));
> +			if (bv_len) {
> +				eb = eb->next;
> +				goto next_eb;
> +			}
> +
> +			/* Clear the page writeback flag. */
> +			eb = (struct extent_buffer *)page->private;
> +			BUG_ON(!eb); /* Can this even happen? */
> +			do {
> +				if (!eb) {
> +					end_page_writeback(page);
> +					break;
> +				}
> +				if (test_bit(EXTENT_BUFFER_WRITEBACK,
> +					     &eb->bflags))
> +					break;
> +				eb = eb->next;
> +			} while (1);
> +		}
>  	} while (bvec >= bio->bi_io_vec);
>  
>  	bio_put(bio);
> @@ -3202,7 +3254,8 @@ static int write_one_eb(struct extent_buffer *eb,
>  			struct extent_page_data *epd)
>  {
>  	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
> -	u64 offset = eb->start;
> +	u64 start = eb->start;
> +	unsigned long offset = eb->start & (PAGE_CACHE_SIZE - 1);
>  	unsigned long i, num_pages;
>  	unsigned long bio_flags = 0;
>  	int rw = (epd->sync_io ? WRITE_SYNC : WRITE);
> @@ -3219,10 +3272,10 @@ static int write_one_eb(struct extent_buffer *eb,
>  
>  		clear_page_dirty_for_io(p);
>  		set_page_writeback(p);
> -		ret = submit_extent_page(rw, eb->tree, p, offset >> 9,
> -					 PAGE_CACHE_SIZE, 0, bdev, &epd->bio,
> -					 -1, end_bio_extent_buffer_writepage,
> -					 0, epd->bio_flags, bio_flags);
> +		ret = submit_extent_page(rw, eb->tree, p, start >> 9, eb->len,
> +					offset, bdev, &epd->bio, -1,
> +					end_bio_extent_buffer_writepage, 0,
> +					epd->bio_flags, bio_flags);
>  		epd->bio_flags = bio_flags;
>  		if (ret) {
>  			set_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
> @@ -3232,7 +3285,7 @@ static int write_one_eb(struct extent_buffer *eb,
>  			ret = -EIO;
>  			break;
>  		}
> -		offset += PAGE_CACHE_SIZE;
> +		start += PAGE_CACHE_SIZE;
>  		update_nr_written(p, wbc, 1);
>  		unlock_page(p);
>  	}
> @@ -3252,7 +3305,7 @@ int btree_write_cache_pages(struct address_space *mapping,
>  {
>  	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
>  	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
> -	struct extent_buffer *eb, *prev_eb = NULL;
> +	struct extent_buffer *eb, *next, *prev_eb = NULL;
>  	struct extent_page_data epd = {
>  		.bio = NULL,
>  		.tree = tree,
> @@ -3326,17 +3379,41 @@ retry:
>  				spin_unlock(&mapping->private_lock);
>  				continue;
>  			}
> +			prev_eb = eb;
> +
> +next_eb:
> +			next = eb->next;
>  
>  			ret = atomic_inc_not_zero(&eb->refs);
> -			spin_unlock(&mapping->private_lock);
> -			if (!ret)
> -				continue;
> +			if (eb->len >= PAGE_SIZE) {
> +				spin_unlock(&mapping->private_lock);
> +				if (!ret)
> +					continue;
> +			} else {
> +				if (!ret)
> +					goto inc_eb;
> +				spin_unlock(&mapping->private_lock);
> +
> +				if (!test_bit(EXTENT_BUFFER_DIRTY,
> +					      &eb->bflags)) {
> +					spin_lock(&mapping->private_lock);
> +					atomic_dec(&eb->refs);
> +					ret = 0;
> +					goto inc_eb;
> +				}
> +			}
>  
> -			prev_eb = eb;
>  			ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
>  			if (!ret) {
> +				if (!(eb->len >= PAGE_SIZE))
> +					spin_lock(&mapping->private_lock);
> +
>  				free_extent_buffer(eb);
> -				continue;
> +
> +				if (eb->len >= PAGE_SIZE)
> +					continue;
> +				else
> +					goto inc_eb;
>  			}
>  
>  			ret = write_one_eb(eb, fs_info, wbc, &epd);
> @@ -3345,8 +3422,26 @@ retry:
>  				free_extent_buffer(eb);
>  				break;
>  			}
> +
> +			if (eb->len >= PAGE_SIZE) {
> +				free_extent_buffer(eb);
> +				goto written;
> +			}
> +
> +			if (next)
> +				spin_lock(&mapping->private_lock);
>  			free_extent_buffer(eb);
>  
> +inc_eb:
> +			if (!next) {
> +				if (spin_is_locked(&mapping->private_lock))
> +					spin_unlock(&mapping->private_lock);
> +				goto written;
> +			}
> +			eb = next;
> +			goto next_eb;
> +
> +written:
>  			/*
>  			 * the filesystem may choose to bump up nr_to_write.
>  			 * We have to make sure to honor the new nr_to_write
> @@ -4000,6 +4095,18 @@ static void __free_extent_buffer(struct extent_buffer *eb)
>  	kmem_cache_free(extent_buffer_cache, eb);
>  }
>  
> +/* Helper function to free extent buffers when there are multiple
> + * extent buffers per page. */
> +static void __free_extent_buffers(struct extent_buffer *eb)
> +{
> +	struct extent_buffer *next;
> +
> +	do {
> +		next = eb->next;
> +		__free_extent_buffer(eb);
> +	} while ((eb = next));
> +}
> +
>  static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>  						   u64 start,
>  						   unsigned long len,
> @@ -4017,6 +4124,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>  	eb->len = len;
>  	eb->tree = tree;
>  	eb->bflags = 0;
> +	eb->next = NULL;
>  	rwlock_init(&eb->lock);
>  	atomic_set(&eb->write_locks, 0);
>  	atomic_set(&eb->read_locks, 0);
> @@ -4054,6 +4162,62 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>  	return eb;
>  }
>  
> +/* Allocates an array of extent buffers for the specified page.
> + * Should be called with the mapping's spin lock set. */
> +static struct extent_buffer *__alloc_extent_buffers(struct extent_io_tree *tree,
> +						    struct page *page,
> +						    gfp_t mask)
> +{
> +	u32 blocksize_bits;
> +	struct btrfs_inode *inode;
> +	struct extent_buffer *eb_head;
> +	struct extent_buffer *eb_cur;
> +	u64 start;
> +	unsigned long len;
> +	int i;
> +
> +	/* Initialize variables. */
> +	inode = BTRFS_I(tree->mapping->host);
> +	blocksize_bits = inode->vfs_inode.i_sb->s_blocksize_bits;
> +
> +	/* Calculate extent buffer dimensions. */
> +	start = page->index << PAGE_CACHE_SHIFT;
> +	len = inode->root->leafsize;
> +
> +	/* Allocate the head extent buffer. */
> +	eb_head = __alloc_extent_buffer(tree, start, len, GFP_NOFS);
> +	if (!eb_head) {
> +		WARN_ON(1);
> +		return NULL;
> +	}
> +	start += len;
> +	eb_head->pages[0] = page;
> +	eb_cur = eb_head;
> +
> +	/* Allocate the other extent buffers. */
> +	for (i = 1; i < (PAGE_CACHE_SIZE >> blocksize_bits); i++) {
> +		eb_cur->next = __alloc_extent_buffer(tree, start, len,
> +						     GFP_NOFS);
> +		if (!eb_cur->next) {
> +			WARN_ON(1);
> +			goto free_ebs;
> +		}
> +		start += len;
> +		eb_cur = eb_cur->next;
> +		eb_cur->pages[0] = page;
> +	}
> +
> +	/* Return the extent buffer head. */
> +	return eb_head;
> +
> +free_ebs:
> +	/* Free each extent buffer. */
> +	// TODO: Implement.
> +	pr_crit(KERN_CRIT "HACK: Need to implement this...\n");
> +	WARN_ON(1);
> +	return NULL;
> +}
> +
>  struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
>  {
>  	unsigned long i;
> @@ -4170,12 +4334,121 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
>  }
>  
>  /*
> + * Frees the page if all extent buffers belonging to the page are not
> + * referernced. The extent buffers themselves must be free afterwards, too...
> + * ret:	0 if the page did not need to be freed; 1 if the page was freed.
> + */
> +static int btrfs_release_extent_buffers_page(struct extent_buffer *eb,
> +						struct extent_buffer **eb_head)
> +{
> +	struct extent_buffer *eb_cur;
> +	struct extent_buffer *eb_temp;
> +	struct page *page;
> +	int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
> +	int ret = 0;
> +
> +	if (extent_buffer_under_io(eb))
> +		BUG_ON(1);
> +
> +	// ...is this even possible?
> +	if (!num_extent_pages(eb->start, eb->len)) {
> +		WARN_ON(1);
> +		return ret;
> +	}
> +
> +	page = extent_buffer_page(eb, 0);
> +	if (page && mapped) {
> +		spin_lock(&page->mapping->private_lock);
> +		/*
> +		 * We do this since we'll remove the pages after we've
> +		 * removed the eb from the radix tree, so we could race
> +		 * and have this page now attached to the new eb.  So
> +		 * only clear page_private if it's still connected to
> +		 * this eb.
> +		 */
> +		if (!PagePrivate(page)) {
> +			spin_unlock(&page->mapping->private_lock);
> +		} else {
> +			/* Find the page eb corresponding to our eb. */
> +			eb_cur = (struct extent_buffer *)page->private;
> +			while (eb_cur->start != eb->start) {
> +				eb_cur = eb_cur->next;
> +				BUG_ON(!eb_cur);
> +			}
> +
> +			/* See if a new eb has been attached to the page. */
> +			if (eb_cur != eb) {
> +				spin_unlock(&page->mapping->private_lock);
> +				ret = 1;
> +				goto page_release;
> +			}
> +
> +			/* See if any other extent_buffer is using the page. */
> +			eb_cur = (struct extent_buffer *)page->private;
> +			do {
> +				/* Check for any other references on the eb. */
> +				spin_lock(&eb_cur->refs_lock);
> +				if (!atomic_dec_and_test(&eb_cur->refs)) {
> +					atomic_inc(&eb_cur->refs);
> +					spin_unlock(&eb_cur->refs_lock);
> +					eb_temp = eb_cur;
> +					eb_cur = (struct extent_buffer *)
> +						 page->private;
> +					while (eb_cur != eb_temp) {
> +						atomic_inc(&eb_cur->refs);
> +						eb_cur = eb_cur->next;
> +					}
> +					spin_unlock(
> +						&page->mapping->private_lock);
> +					goto page_release;
> +				}
> +				spin_unlock(&eb_cur->refs_lock);
> +			} while ((eb_cur = eb_cur->next) != NULL);
> +
> +			/* Sanity checks. */
> +			eb_cur = (struct extent_buffer *)page->private;
> +			do {
> +				BUG_ON(extent_buffer_under_io(eb_cur));
> +			} while ((eb_cur = eb_cur->next) != NULL);
> +			BUG_ON(PageDirty(page));
> +			BUG_ON(PageWriteback(page));
> +			/*
> +			 * We need to make sure we haven't been attached
> +			 * to a new eb.
> +			 */
> +			eb_cur = (struct extent_buffer *)page->private;
> +			*eb_head = eb_cur;
> +			eb_temp = NULL;
> +			ClearPagePrivate(page);
> +			set_page_private(page, 0);
> +			/* One for the page private. */
> +			page_cache_release(page);
> +			ret = 1;
> +			spin_unlock(&page->mapping->private_lock);
> +		}
> +	}
> +
> +page_release:
> +	if (page) {
> +		/* One for when we alloced the page */
> +		page_cache_release(page);
> +	}
> +	return ret;
> +}
> +
> +/*
>   * Helper for releasing the extent buffer.
>   */
>  static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
>  {
> -	btrfs_release_extent_buffer_page(eb, 0);
> -	__free_extent_buffer(eb);
> +	if (eb->len >= PAGE_SIZE) {
> +		btrfs_release_extent_buffer_page(eb, 0);
> +		__free_extent_buffer(eb);
> +	} else {
> +		struct extent_buffer *eb_head;
> +		if (btrfs_release_extent_buffers_page(eb, &eb_head))
> +			__free_extent_buffers(eb_head);
> +	}
>  }
>  
>  static void check_buffer_tree_ref(struct extent_buffer *eb)
> @@ -4222,16 +4495,153 @@ static void mark_extent_buffer_accessed(struct extent_buffer *eb)
>  struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
>  					  u64 start, unsigned long len)
>  {
> -	unsigned long num_pages = num_extent_pages(start, len);
> -	unsigned long i;
> -	unsigned long index = start >> PAGE_CACHE_SHIFT;
> +	/* Allocate a new extent_buffer depending on blocksize*/
> +	if (len < PAGE_CACHE_SIZE)
> +		return alloc_extent_buffer_multiple(tree, start, len);
> +	return alloc_extent_buffer_single(tree, start, len);
> +}
> +
> +struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
> +						   u64 start,
> +						   unsigned long len) {
> +
> +	struct address_space *mapping;
> +	u32 blocksize_bits;
> +	struct btrfs_inode *btrfs_inode;
> +	struct extent_buffer *eb_cur;
> +	struct extent_buffer *eb_head;
> +	struct extent_buffer *exists;
> +	unsigned long index;
> +	struct page *page;
> +	int ret;
> +
> +	/* Initialize variables. */
> +	btrfs_inode = BTRFS_I(tree->mapping->host);
> +	blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
> +
> +	/* Sanity checks. */
> +	WARN_ON(num_extent_pages(start, len) > 1);
> +
> +	/* See if the extent_buffer already exists in the radix tree. */
> +	rcu_read_lock();
> +	eb_cur = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
> +	if (eb_cur && atomic_inc_not_zero(&eb_cur->refs)) {
> +		rcu_read_unlock();
> +		mark_extent_buffer_accessed(eb_cur);
> +		return eb_cur;
> +	}
> +	rcu_read_unlock();
> +
> +	/* Find the page in the mapping. */
> +	index = start >> PAGE_CACHE_SHIFT;
> +	mapping = tree->mapping;
> +	page = find_or_create_page(mapping, index, GFP_NOFS);
> +	if (!page) {
> +		WARN_ON(1);
> +		return NULL;
> +	}
> +
> +	/* Allocate each extent buffer for the page. */
> +	eb_head = __alloc_extent_buffers(tree, page, GFP_NOFS);
> +	if (!eb_head) {
> +		WARN_ON(1);
> +		return NULL;
> +	}
> +
> +	/* See if extent buffers have already been allocated for
> +	 * this page. */
> +	spin_lock(&mapping->private_lock);
> +	if (PagePrivate(page)) {
> +		/*
> +		 * We could have already allocated an eb for this page
> +		 * and attached one so lets see if we can get a ref on
> +		 * the existing eb, and if we can we know it's good and
> +		 * we can just return that one, else we know we can just
> +		 * overwrite page->private.
> +		 */
> +		eb_cur = (struct extent_buffer *)page->private;
> +		while (eb_cur->start != start) {
> +			eb_cur = eb_cur->next;
> +			BUG_ON(!eb_cur);
> +		}
> +		check_buffer_tree_ref(eb_cur);
> +		spin_unlock(&mapping->private_lock);
> +		unlock_page(page);
> +		mark_extent_buffer_accessed(eb_cur);
> +		__free_extent_buffers(eb_head);
> +		return eb_cur;
> +	}
> +
> +	/* Bind the extent buffer to the page. */
> +	attach_extent_buffer_page(eb_head, page);
> +	spin_unlock(&mapping->private_lock);
> +	WARN_ON(PageDirty(page));
> +	mark_page_accessed(page);
> +
> +again:
> +	/* Set eb_cur to the buffer added. */
> +	eb_cur = eb_head;
> +	while (start != eb_cur->start) {
> +		eb_cur = eb_cur->next;
> +		BUG_ON(!eb_cur);
> +	}
> +
> +	/* Preload the radix tree. */
> +	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
> +	if (ret) {
> +		WARN_ON(1);
> +		return NULL;
> +	}
> +
> +	/* Add the extent buffer to the radix tree. */
> +	spin_lock(&tree->buffer_lock);
> +	ret = radix_tree_insert(&tree->buffer,
> +				eb_cur->start >> blocksize_bits,
> +				eb_cur);
> +	if (ret == -EEXIST) {
> +		exists = radix_tree_lookup(&tree->buffer,
> +				eb_cur->start >> blocksize_bits);
> +		if (exists->start != start)
> +			BUG_ON(1);
> +		if (!atomic_inc_not_zero(&exists->refs)) {
> +			spin_unlock(&tree->buffer_lock);
> +			radix_tree_preload_end();
> +			exists = NULL;
> +			goto again;
> +		}
> +		spin_unlock(&tree->buffer_lock);
> +		radix_tree_preload_end();
> +		mark_extent_buffer_accessed(exists);
> +		WARN_ON(!atomic_dec_and_test(&eb_cur->refs));
> +		btrfs_release_extent_buffer(eb_cur);
> +		return exists;
> +	}
> +
> +	/* Set the extent buffer's tree-reference bits. */
> +	check_buffer_tree_ref(eb_cur);
> +	spin_unlock(&tree->buffer_lock);
> +	radix_tree_preload_end();
> +
> +	/* Not quite sure what this does. */
> +	SetPageChecked(eb_head->pages[0]);
> +	unlock_page(eb_head->pages[0]);
> +
> +	return eb_cur;
> +}
> +
> +struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
> +						 u64 start, unsigned long len) {
> +	struct address_space *mapping = tree->mapping;
>  	struct extent_buffer *eb;
>  	struct extent_buffer *exists = NULL;
> +	unsigned long i;
> +	unsigned long index = start >> PAGE_CACHE_SHIFT;
> +	unsigned long num_pages = num_extent_pages(start, len);
>  	struct page *p;
> -	struct address_space *mapping = tree->mapping;
>  	int uptodate = 1;
>  	int ret;
>  
> +	/* See if the extent_buffer already exists */
>  	rcu_read_lock();
>  	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
>  	if (eb && atomic_inc_not_zero(&eb->refs)) {
> @@ -4350,9 +4760,17 @@ struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
>  					 u64 start, unsigned long len)
>  {
>  	struct extent_buffer *eb;
> +	struct btrfs_inode *btrfs_inode = BTRFS_I(tree->mapping->host);
> +	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
>  
>  	rcu_read_lock();
> -	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
> +	// This branch needs to be fixed when the allocation code is merged.
> +	// Seriously.
> +	if (blocksize_bits >= PAGE_CACHE_SHIFT)
> +		eb = radix_tree_lookup(&tree->buffer,
> +				       start >> PAGE_CACHE_SHIFT);
> +	else
> +		eb = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
>  	if (eb && atomic_inc_not_zero(&eb->refs)) {
>  		rcu_read_unlock();
>  		mark_extent_buffer_accessed(eb);
> @@ -4371,9 +4789,25 @@ static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
>  	__free_extent_buffer(eb);
>  }
>  
> -/* Expects to have eb->eb_lock already held */
> +/*
> + * The RCU head must point to the first extent buffer belonging to a page.
> + */
> +static inline void btrfs_release_extent_buffers_rcu(struct rcu_head *head)
> +{
> +	struct extent_buffer *eb =
> +			container_of(head, struct extent_buffer, rcu_head);
> +
> +	do {
> +		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
> +	} while ((eb = eb->next));
> +}
> +
> +/* Expects to have eb->refs_lock already held */
>  static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
>  {
> +	struct btrfs_inode *btrfs_inode = BTRFS_I(eb->tree->mapping->host);
> +	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
> +
>  	WARN_ON(atomic_read(&eb->refs) == 0);
>  	if (atomic_dec_and_test(&eb->refs)) {
>  		if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
> @@ -4381,17 +4815,35 @@ static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
>  		} else {
>  			struct extent_io_tree *tree = eb->tree;
>  
> +			/* Dumb hack to make releasing the page easier. */
> +			if (eb->len < PAGE_SIZE)
> +				atomic_inc(&eb->refs);
> +
>  			spin_unlock(&eb->refs_lock);
>  
> +			// This also needs to be fixed when allocation code is
> +			// merged.
>  			spin_lock(&tree->buffer_lock);
> -			radix_tree_delete(&tree->buffer,
> -					  eb->start >> PAGE_CACHE_SHIFT);
> +			if (eb->len >= PAGE_SIZE)
> +				radix_tree_delete(&tree->buffer,
> +					  eb->start >> blocksize_bits);
> +			else
> +				radix_tree_delete(&tree->buffer,
> +					  eb->start >> blocksize_bits);
>  			spin_unlock(&tree->buffer_lock);
>  		}
>  
>  		/* Should be safe to release our pages at this point */
> -		btrfs_release_extent_buffer_page(eb, 0);
> -		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
> +		if (eb->len >= PAGE_SIZE) {
> +			btrfs_release_extent_buffer_page(eb, 0);
> +			call_rcu(&eb->rcu_head,
> +				 btrfs_release_extent_buffer_rcu);
> +		} else {
> +			struct extent_buffer *eb_head;
> +			if (btrfs_release_extent_buffers_page(eb, &eb_head))
> +				btrfs_release_extent_buffers_rcu(
> +							&eb_head->rcu_head);
> +		}
>  		return 1;
>  	}
>  	spin_unlock(&eb->refs_lock);
> @@ -4482,6 +4934,11 @@ int set_extent_buffer_dirty(struct extent_buffer *eb)
>  
>  	for (i = 0; i < num_pages; i++)
>  		set_page_dirty(extent_buffer_page(eb, i));
> +	/* Run an additional sanity check here instead of
> +	 * in btree_set_page_dirty() since we can't get the eb there for
> +	 * subpage blocksize. */
> +	if (eb->len < PAGE_SIZE)
> +		btrfs_assert_tree_locked(eb);
>  	return was_dirty;
>  }
>  
> @@ -4503,11 +4960,14 @@ int clear_extent_buffer_uptodate(struct extent_buffer *eb)
>  	unsigned long num_pages;
>  
>  	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
> -	num_pages = num_extent_pages(eb->start, eb->len);
> -	for (i = 0; i < num_pages; i++) {
> -		page = extent_buffer_page(eb, i);
> -		if (page)
> -			ClearPageUptodate(page);
> +	/* Ignore the page's uptodate flag forsubpage blocksize. */
> +	if (eb->len >= PAGE_SIZE) {
> +		num_pages = num_extent_pages(eb->start, eb->len);
> +		for (i = 0; i < num_pages; i++) {
> +			page = extent_buffer_page(eb, i);
> +			if (page)
> +				ClearPageUptodate(page);
> +		}
>  	}
>  	return 0;
>  }
> @@ -4518,11 +4978,16 @@ int set_extent_buffer_uptodate(struct extent_buffer *eb)
>  	struct page *page;
>  	unsigned long num_pages;
>  
> +	/* Set extent buffer up-to-date. */
>  	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
> -	num_pages = num_extent_pages(eb->start, eb->len);
> -	for (i = 0; i < num_pages; i++) {
> -		page = extent_buffer_page(eb, i);
> -		SetPageUptodate(page);
> +
> +	/* Set pages up-to-date. */
> +	if (eb->len >= PAGE_CACHE_SIZE) {
> +		num_pages = num_extent_pages(eb->start, eb->len);
> +		for (i = 0; i < num_pages; i++) {
> +			page = extent_buffer_page(eb, i);
> +			SetPageUptodate(page);
> +		}
>  	}
>  	return 0;
>  }
> @@ -4606,7 +5071,7 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
>  		}
>  	}
>  	if (all_uptodate) {
> -		if (start_i == 0)
> +		if (start_i == 0 && eb->len >= PAGE_SIZE)
>  			set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
>  		goto unlock_exit;
>  	}
> @@ -4693,7 +5158,7 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>  			       unsigned long *map_start,
>  			       unsigned long *map_len)
>  {
> -	size_t offset = start & (PAGE_CACHE_SIZE - 1);
> +	size_t offset;
>  	char *kaddr;
>  	struct page *p;
>  	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
> @@ -4709,6 +5174,9 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>  		*map_start = 0;
>  	} else {
>  		offset = 0;
> +		// I'm pretty sure that this is a) just plain wrong and
> +		// b) will never realistically execute; not entirely sure,
> +		// though...
>  		*map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
>  	}
>  
> @@ -4722,7 +5190,7 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>  	p = extent_buffer_page(eb, i);
>  	kaddr = page_address(p);
>  	*map = kaddr + offset;
> -	*map_len = PAGE_CACHE_SIZE - offset;
> +	*map_len = (PAGE_CACHE_SIZE - offset) & (eb->len - 1);
>  	return 0;
>  }
>  
> @@ -4996,6 +5464,7 @@ void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
>  int try_release_extent_buffer(struct page *page, gfp_t mask)
>  {
>  	struct extent_buffer *eb;
> +	int ret;
>  
>  	/*
>  	 * We need to make sure noboody is attaching this page to an eb right
> @@ -5010,30 +5479,61 @@ int try_release_extent_buffer(struct page *page, gfp_t mask)
>  	eb = (struct extent_buffer *)page->private;
>  	BUG_ON(!eb);
>  
> -	/*
> -	 * This is a little awful but should be ok, we need to make sure that
> -	 * the eb doesn't disappear out from under us while we're looking at
> -	 * this page.
> -	 */
> -	spin_lock(&eb->refs_lock);
> -	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
> -		spin_unlock(&eb->refs_lock);
> +	if (eb->len >= PAGE_SIZE) {
> +		/*
> +		 * This is a little awful but should be ok, we need to make
> +		 * sure that the eb doesn't disappear out from under us while
> +		 * we're looking at this page.
> +		 */
> +		spin_lock(&eb->refs_lock);
> +		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
> +			spin_unlock(&eb->refs_lock);
> +			spin_unlock(&page->mapping->private_lock);
> +			return 0;
> +		}
>  		spin_unlock(&page->mapping->private_lock);
> -		return 0;
> -	}
> -	spin_unlock(&page->mapping->private_lock);
>  
> -	if ((mask & GFP_NOFS) == GFP_NOFS)
> -		mask = GFP_NOFS;
> +		if ((mask & GFP_NOFS) == GFP_NOFS)
> +			mask = GFP_NOFS;
>  
> -	/*
> -	 * If tree ref isn't set then we know the ref on this eb is a real ref,
> -	 * so just return, this page will likely be freed soon anyway.
> -	 */
> -	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
> -		spin_unlock(&eb->refs_lock);
> -		return 0;
> -	}
> +		/*
> +		 * If tree ref isn't set then we know the ref on this eb is a
> +		 * real ref, so just return, this page will likely be freed
> +		 * soon anyway.
> +		 */
> +		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
> +			spin_unlock(&eb->refs_lock);
> +			return 0;
> +		}
>  
> -	return release_extent_buffer(eb, mask);
> +		return release_extent_buffer(eb, mask);
> +	} else {
> +		ret = 0;
> +		do {
> +			spin_lock(&eb->refs_lock);
> +			if (atomic_read(&eb->refs) != 1 ||
> +					extent_buffer_under_io(eb)) {
> +				spin_unlock(&eb->refs_lock);
> +				continue;
> +			}
> +			spin_unlock(&page->mapping->private_lock);
> +
> +			if ((mask & GFP_NOFS) == GFP_NOFS)
> +				mask = GFP_NOFS;
> +
> +			if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF,
> +						&eb->bflags)) {
> +				spin_unlock(&eb->refs_lock);
> +				spin_lock(&page->mapping->private_lock);
> +				continue;
> +			}
> +
> +			/* No idea what to do with the 'ret' here. */
> +			ret |= release_extent_buffer(eb, mask);
> +
> +			spin_lock(&page->mapping->private_lock);
> +		} while ((eb = eb->next) != NULL);
> +		spin_unlock(&page->mapping->private_lock);
> +		return ret;
> +	}
>  }
> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
> index 2eacfab..955ef5e 100644
> --- a/fs/btrfs/extent_io.h
> +++ b/fs/btrfs/extent_io.h
> @@ -163,6 +163,9 @@ struct extent_buffer {
>  	wait_queue_head_t lock_wq;
>  	struct page *inline_pages[INLINE_EXTENT_BUFFER_PAGES];
>  	struct page **pages;
> +
> +	/* Acyclic linked list of extent_buffers belonging to a single page. */
> +	struct extent_buffer *next;
>  };
>  
>  static inline void extent_set_compress_type(unsigned long *bio_flags,
> @@ -270,6 +273,10 @@ void set_page_extent_mapped(struct page *page);
>  
>  struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
>  					  u64 start, unsigned long len);
> +struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
> +						 u64 start, unsigned long len);
> +struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
> +						 u64 start, unsigned long len);
>  struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len);
>  struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
>  struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 3bff4d4..8745289 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1340,7 +1340,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>  		}
>  
>  		ret = btrfs_delalloc_reserve_space(inode,
> -					num_pages << PAGE_CACHE_SHIFT);
> +					write_bytes);
>  		if (ret)
>  			break;
>  
> @@ -1354,7 +1354,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>  				    force_page_uptodate);
>  		if (ret) {
>  			btrfs_delalloc_release_space(inode,
> -					num_pages << PAGE_CACHE_SHIFT);
> +					write_bytes);
>  			break;
>  		}
>  
> @@ -1392,8 +1392,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>  				spin_unlock(&BTRFS_I(inode)->lock);
>  			}
>  			btrfs_delalloc_release_space(inode,
> -					(num_pages - dirty_pages) <<
> -					PAGE_CACHE_SHIFT);
> +						write_bytes - copied);
>  		}
>  
>  		if (copied > 0) {
> @@ -1402,7 +1401,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>  						NULL);
>  			if (ret) {
>  				btrfs_delalloc_release_space(inode,
> -					dirty_pages << PAGE_CACHE_SHIFT);
> +						copied);
>  				btrfs_drop_pages(pages, num_pages);
>  				break;
>  			}
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 59ea2e4..1c0e254 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -960,6 +960,8 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
>  
>  	if (block_group)
>  		start = block_group->key.objectid;
> +	else // Hmm I don't recall putting this here.
> +		start = (u64)-1;
>  
>  	while (block_group && (start < block_group->key.objectid +
>  			       block_group->key.offset)) {
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 3368c10..11ff3dd 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -2040,22 +2040,38 @@ static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  	struct btrfs_ordered_extent *ordered_extent = NULL;
>  	struct btrfs_workers *workers;
> +	u64 block_size = 1 << inode->i_blkbits;
> +	u64 io_size;
> +
> +	if (block_size >= PAGE_CACHE_SIZE)
> +		io_size = end - start + 1;
> +	else
> +		io_size = block_size;
>  
>  	trace_btrfs_writepage_end_io_hook(page, start, end, uptodate);
>  
>  	ClearPagePrivate2(page);
> -	if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
> -					    end - start + 1, uptodate))
> -		return 0;
> -
> -	ordered_extent->work.func = finish_ordered_fn;
> -	ordered_extent->work.flags = 0;
> -
> -	if (btrfs_is_free_space_inode(inode))
> -		workers = &root->fs_info->endio_freespace_worker;
> -	else
> -		workers = &root->fs_info->endio_write_workers;
> -	btrfs_queue_worker(workers, &ordered_extent->work);
> +next_block:
> +	if (btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
> +					    io_size, uptodate)) {
> +		ordered_extent->work.func = finish_ordered_fn;
> +		ordered_extent->work.flags = 0;
> +
> +		if (btrfs_is_free_space_inode(inode))
> +			workers = &root->fs_info->endio_freespace_worker;
> +		else
> +			workers = &root->fs_info->endio_write_workers;
> +		btrfs_queue_worker(workers, &ordered_extent->work);
> +	}
> +
> +	// I think that writes are always block-size granularity.
> +	if (block_size < PAGE_CACHE_SIZE)
> +		BUG_ON(start & (io_size - 1)); // Welp, one way to make sure...
> +	start += io_size;
> +	if (start < end)
> +		goto next_block;
> +	// We overshot. I'm pretty sure that this is terrible.
> +	BUG_ON(start != (end + 1));
>  
>  	return 0;
>  }
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 657d83c..c0269df 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3937,8 +3937,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>  		return btrfs_ioctl_qgroup_create(file, argp);
>  	case BTRFS_IOC_QGROUP_LIMIT:
>  		return btrfs_ioctl_qgroup_limit(file, argp);
> -	case BTRFS_IOC_DEV_REPLACE:
> -		return btrfs_ioctl_dev_replace(root, argp);
> +	//case BTRFS_IOC_DEV_REPLACE:
> +//		return btrfs_ioctl_dev_replace(root, argp);
>  	}
>  
>  	return -ENOTTY;
> -- 
> 1.7.1
> 
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Miao Xie Dec. 18, 2012, 8:49 a.m. UTC | #2

On tue, 18 Dec 2012 15:30:51 +0800, Liu Bo wrote:
> On Mon, Dec 17, 2012 at 11:13:25PM -0800, [e-mail] wrote:
>> From: Wade Cline <[e-mail]>
>>
>> v1 -> v2:
>> - Added Signed-off-by tag (it's kind of important).
>>
>> This patch is only an RFC. My internship is ending and I was hoping
>> to get some feedback and incorporate any suggestions people may
>> have before my internship ends along with life as we know it (this
>> Friday).
>>
>> The filesystem should mount/umount properly but tends towards the
>> explosive side when writes start happening. My current focus is on
>> checksumming issues and also an error when releasing extent buffers
>> when creating a large file with 'dd'... and probably any other
>> method. There's still a significant amount of work that needs to be
>> done before this should be incorporated into mainline.
>>
>> A couple of notes:
>>     - Based off of Josef's btrfs-next branch, commit
>>       8d089a86e45b34d7bc534d955e9d8543609f7e42
>>     - C99-style comments are "meta-comments" where I'd like more
>>       feedback; they aren't permanent but make 'checkpatch' moan.
>>     - extent_buffer allocation and freeing need their code paths
>>       merged; they're currently in separate functions and are both
>>       very ugly.
>>     - The patch itself will eventually need to be broken down
>>       into smaller pieces if at all possible...
> 
> Could you please first elaborate why we need this subpagesize stuff and
> any user case in this patch's commit log?
> Or Am I missing something?

It is used on the machines on which the page size is larger than 4KB (Such as powerpc)

Thanks
Miao

> 
> thanks,
> liubo
> 
>>
>> Signed-off-by: Wade Cline <[e-mail]>
>> ---
>>  fs/btrfs/ctree.h            |   11 +-
>>  fs/btrfs/disk-io.c          |  110 +++++++--
>>  fs/btrfs/extent_io.c        |  632 ++++++++++++++++++++++++++++++++++++++-----
>>  fs/btrfs/extent_io.h        |    7 +
>>  fs/btrfs/file.c             |    9 +-
>>  fs/btrfs/free-space-cache.c |    2 +
>>  fs/btrfs/inode.c            |   38 ++-
>>  fs/btrfs/ioctl.c            |    4 +-
>>  8 files changed, 709 insertions(+), 104 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index fbaaf20..c786a58 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -1938,14 +1938,19 @@ static inline void btrfs_set_token_##name(struct extent_buffer *eb,	\
>>  #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)		\
>>  static inline u##bits btrfs_##name(struct extent_buffer *eb)		\
>>  {									\
>> -	type *p = page_address(eb->pages[0]);				\
>> -	u##bits res = le##bits##_to_cpu(p->member);			\
>> +	type *p;							\
>> +	u##bits res;							\
>> +									\
>> +	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
>> +	res = le##bits##_to_cpu(p->member);				\
>>  	return res;							\
>>  }									\
>>  static inline void btrfs_set_##name(struct extent_buffer *eb,		\
>>  				    u##bits val)			\
>>  {									\
>> -	type *p = page_address(eb->pages[0]);				\
>> +	type *p;							\
>> +									\
>> +	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
>>  	p->member = cpu_to_le##bits(val);				\
>>  }
>>  
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index f633af8..00b80b7 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -373,6 +373,24 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>>  					       WAIT_COMPLETE,
>>  					       btree_get_extent, mirror_num);
>>  		if (!ret) {
>> +			/*
>> +			 * I think that this is bad and should be moved
>> +			 * into btree_readpage_end_io_hook(), but that
>> +			 * it should apply to a single block at a time.
>> +			 * That may be difficult and would make the
>> +			 * function name a misnomer, but mostly I hate
>> +			 * the silly goto.
>> +			 */
>> +			if (eb->len < PAGE_SIZE &&
>> +			    !extent_buffer_uptodate(eb)) {
>> +				if (csum_tree_block(root, eb, 1)) {
>> +					ret = -EIO;
>> +					goto bad;
>> +				} else {
>> +					set_extent_buffer_uptodate(eb);
>> +				}
>> +			}
>> +
>>  			if (!verify_parent_transid(io_tree, eb,
>>  						   parent_transid, 0))
>>  				break;
>> @@ -385,6 +403,7 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>>  		 * there is no reason to read the other copies, they won't be
>>  		 * any less wrong.
>>  		 */
>> +bad:
>>  		if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
>>  			break;
>>  
>> @@ -416,29 +435,55 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
>>   * checksum a dirty tree block before IO.  This has extra checks to make sure
>>   * we only fill in the checksum field in the first page of a multi-page block
>>   */
>> -
>> -static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
>> +static int csum_dirty_buffer(struct btrfs_root *root, struct page *page,
>> +			     unsigned int offset, unsigned int len)
>>  {
>> -	struct extent_io_tree *tree;
>>  	u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
>>  	u64 found_start;
>>  	struct extent_buffer *eb;
>>  
>> -	tree = &BTRFS_I(page->mapping->host)->io_tree;
>> +	if (!PageUptodate(page)) {
>> +		WARN_ON(1);
>> +		return 0;
>> +	}
>>  
>>  	eb = (struct extent_buffer *)page->private;
>> -	if (page != eb->pages[0])
>> -		return 0;
>> +	if (eb->len >= PAGE_SIZE) {
>> +		if (eb->pages[0] != page)
>> +			return 0;
>> +	} else {
>> +		start += offset;
>> +		while (eb->start != start) {
>> +			eb = eb->next;
>> +			BUG_ON(!eb);
>> +		}
>> +next:
>> +		if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>> +			WARN_ON(1);
>> +		if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
>> +			WARN_ON(1);
>> +		if (eb->pages[0] != page)
>> +			WARN_ON(1);
>> +	}
>> +
>>  	found_start = btrfs_header_bytenr(eb);
>>  	if (found_start != start) {
>>  		WARN_ON(1);
>>  		return 0;
>>  	}
>> -	if (!PageUptodate(page)) {
>> -		WARN_ON(1);
>> -		return 0;
>> -	}
>> +
>>  	csum_tree_block(root, eb, 0);
>> +
>> +	if (eb->len < PAGE_SIZE) {
>> +		len -= eb->len;
>> +		BUG_ON(len & (eb->len - 1));
>> +		if (len) {
>> +			start += eb->len;
>> +			eb = eb->next;
>> +			goto next;
>> +		}
>> +	}
>> +
>>  	return 0;
>>  }
>>  
>> @@ -579,6 +624,19 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>>  
>>  	tree = &BTRFS_I(page->mapping->host)->io_tree;
>>  	eb = (struct extent_buffer *)page->private;
>> +	if (eb->len < PAGE_SIZE) {
>> +		/* Find the eb that tried to submit a read request. This is
>> +		 * a little bit funky. */
>> +		do {
>> +			if (!atomic_read(&eb->io_pages))
>> +				continue;
>> +			if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags) ||
>> +			    test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>> +				continue;
>> +			break;
>> +		} while ((eb = eb->next));
>> +		BUG_ON(!eb);
>> +	}
>>  
>>  	/* the pending IO might have been the only thing that kept this buffer
>>  	 * in memory.  Make sure we have a ref for all this other checks
>> @@ -615,8 +673,11 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>>  	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb),
>>  				       eb, found_level);
>>  
>> -	ret = csum_tree_block(root, eb, 1);
>> -	if (ret) {
>> +	/*
>> +	 * Subpagesize blocksize checksumming is currently done in
>> +	 * btree_read_extent_buffer_pages().
>> +	 */
>> +	if (eb->len >= PAGE_SIZE && csum_tree_block(root, eb, 1)) {
>>  		ret = -EIO;
>>  		goto err;
>>  	}
>> @@ -631,8 +692,15 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
>>  		ret = -EIO;
>>  	}
>>  
>> -	if (!ret)
>> +	/*
>> +	 * For subpagesize blocksize, only the page needs to be set
>> +	 * up-to-date; each extent_buffer is set up-to-date when it is
>> +	 * checksummed.
>> +	 */
>> +	if (eb->len >= PAGE_SIZE)
>>  		set_extent_buffer_uptodate(eb);
>> +	else
>> +		SetPageUptodate(eb->pages[0]);
>>  err:
>>  	if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
>>  		clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
>> @@ -828,7 +896,8 @@ static int btree_csum_one_bio(struct bio *bio)
>>  	WARN_ON(bio->bi_vcnt <= 0);
>>  	while (bio_index < bio->bi_vcnt) {
>>  		root = BTRFS_I(bvec->bv_page->mapping->host)->root;
>> -		ret = csum_dirty_buffer(root, bvec->bv_page);
>> +		ret = csum_dirty_buffer(root, bvec->bv_page, bvec->bv_offset,
>> +					bvec->bv_len);
>>  		if (ret)
>>  			break;
>>  		bio_index++;
>> @@ -1007,9 +1076,13 @@ static int btree_set_page_dirty(struct page *page)
>>  	BUG_ON(!PagePrivate(page));
>>  	eb = (struct extent_buffer *)page->private;
>>  	BUG_ON(!eb);
>> -	BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
>> -	BUG_ON(!atomic_read(&eb->refs));
>> -	btrfs_assert_tree_locked(eb);
>> +	/* There doesn't seem to be a method for passing the correct eb
>> +	 * to this function, so no sanity checks for subpagesize blocksize. */
>> +	if (eb->len >= PAGE_SIZE) {
>> +		BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
>> +		BUG_ON(!atomic_read(&eb->refs));
>> +		btrfs_assert_tree_locked(eb);
>> +	}
>>  #endif
>>  	return __set_page_dirty_nobuffers(page);
>>  }
>> @@ -2400,11 +2473,14 @@ int open_ctree(struct super_block *sb,
>>  		goto fail_sb_buffer;
>>  	}
>>  
>> +#if 0
>> +	// Hmm. How to deal wth this for subpagesize blocksize?
>>  	if (sectorsize != PAGE_SIZE) {
>>  		printk(KERN_WARNING "btrfs: Incompatible sector size(%lu) "
>>  		       "found on %s\n", (unsigned long)sectorsize, sb->s_id);
>>  		goto fail_sb_buffer;
>>  	}
>> +#endif
>>  
>>  	mutex_lock(&fs_info->chunk_mutex);
>>  	ret = btrfs_read_sys_array(tree_root);
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 1b319df..c1e052e 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -2519,7 +2519,7 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>>  	int contig = 0;
>>  	int this_compressed = bio_flags & EXTENT_BIO_COMPRESSED;
>>  	int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
>> -	size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);
>> +	size_t bio_size = min_t(size_t, size, PAGE_CACHE_SIZE);
>>  
>>  	if (bio_ret && *bio_ret) {
>>  		bio = *bio_ret;
>> @@ -2530,8 +2530,8 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>>  				sector;
>>  
>>  		if (prev_bio_flags != bio_flags || !contig ||
>> -		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
>> -		    bio_add_page(bio, page, page_size, offset) < page_size) {
>> +		    merge_bio(tree, page, offset, bio_size, bio, bio_flags) ||
>> +		    bio_add_page(bio, page, bio_size, offset) < bio_size) {
>>  			ret = submit_one_bio(rw, bio, mirror_num,
>>  					     prev_bio_flags);
>>  			if (ret < 0)
>> @@ -2550,7 +2550,7 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
>>  	if (!bio)
>>  		return -ENOMEM;
>>  
>> -	bio_add_page(bio, page, page_size, offset);
>> +	bio_add_page(bio, page, bio_size, offset);
>>  	bio->bi_end_io = end_io_func;
>>  	bio->bi_private = tree;
>>  
>> @@ -3168,14 +3168,28 @@ static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
>>  	int uptodate = err == 0;
>>  	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
>>  	struct extent_buffer *eb;
>> +	unsigned int offset;
>> +	unsigned int bv_len;
>> +	u64 start;
>>  	int done;
>>  
>>  	do {
>>  		struct page *page = bvec->bv_page;
>> +		offset = bvec->bv_offset;
>> +		bv_len = bvec->bv_len;
>> +		start = ((u64)page->index << PAGE_CACHE_SHIFT) + offset;
>>  
>>  		bvec--;
>>  		eb = (struct extent_buffer *)page->private;
>>  		BUG_ON(!eb);
>> +		if (eb->len < PAGE_SIZE) {
>> +			while (eb->start != start) {
>> +				eb = eb->next;
>> +				BUG_ON(!eb);
>> +			}
>> +		}
>> +
>> +next_eb:
>>  		done = atomic_dec_and_test(&eb->io_pages);
>>  
>>  		if (!uptodate || test_bit(EXTENT_BUFFER_IOERR, &eb->bflags)) {
>> @@ -3184,12 +3198,50 @@ static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
>>  			SetPageError(page);
>>  		}
>>  
>> -		end_page_writeback(page);
>> +		if (eb->len >= PAGE_SIZE) {
>> +			end_page_writeback(page);
>>  
>> -		if (!done)
>> -			continue;
>> +			if (!done)
>> +				continue;
>>  
>> -		end_extent_buffer_writeback(eb);
>> +			end_extent_buffer_writeback(eb);
>> +		} else {
>> +			/* Sanity checks. */
>> +			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>> +				WARN_ON(1);
>> +
>> +			/* Ensure I/O page count is zero. */
>> +			if (!done)
>> +				WARN_ON(1);
>> +
>> +			/* Clear the extent buffer's writeback flag. */
>> +			end_extent_buffer_writeback(eb);
>> +
>> +			/*
>> +			 * See if any other extent buffers exists within the
>> +			 * page.
>> +			 */
>> +			bv_len -= eb->len;
>> +			BUG_ON(bv_len & (eb->len - 1));
>> +			if (bv_len) {
>> +				eb = eb->next;
>> +				goto next_eb;
>> +			}
>> +
>> +			/* Clear the page writeback flag. */
>> +			eb = (struct extent_buffer *)page->private;
>> +			BUG_ON(!eb); /* Can this even happen? */
>> +			do {
>> +				if (!eb) {
>> +					end_page_writeback(page);
>> +					break;
>> +				}
>> +				if (test_bit(EXTENT_BUFFER_WRITEBACK,
>> +					     &eb->bflags))
>> +					break;
>> +				eb = eb->next;
>> +			} while (1);
>> +		}
>>  	} while (bvec >= bio->bi_io_vec);
>>  
>>  	bio_put(bio);
>> @@ -3202,7 +3254,8 @@ static int write_one_eb(struct extent_buffer *eb,
>>  			struct extent_page_data *epd)
>>  {
>>  	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
>> -	u64 offset = eb->start;
>> +	u64 start = eb->start;
>> +	unsigned long offset = eb->start & (PAGE_CACHE_SIZE - 1);
>>  	unsigned long i, num_pages;
>>  	unsigned long bio_flags = 0;
>>  	int rw = (epd->sync_io ? WRITE_SYNC : WRITE);
>> @@ -3219,10 +3272,10 @@ static int write_one_eb(struct extent_buffer *eb,
>>  
>>  		clear_page_dirty_for_io(p);
>>  		set_page_writeback(p);
>> -		ret = submit_extent_page(rw, eb->tree, p, offset >> 9,
>> -					 PAGE_CACHE_SIZE, 0, bdev, &epd->bio,
>> -					 -1, end_bio_extent_buffer_writepage,
>> -					 0, epd->bio_flags, bio_flags);
>> +		ret = submit_extent_page(rw, eb->tree, p, start >> 9, eb->len,
>> +					offset, bdev, &epd->bio, -1,
>> +					end_bio_extent_buffer_writepage, 0,
>> +					epd->bio_flags, bio_flags);
>>  		epd->bio_flags = bio_flags;
>>  		if (ret) {
>>  			set_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
>> @@ -3232,7 +3285,7 @@ static int write_one_eb(struct extent_buffer *eb,
>>  			ret = -EIO;
>>  			break;
>>  		}
>> -		offset += PAGE_CACHE_SIZE;
>> +		start += PAGE_CACHE_SIZE;
>>  		update_nr_written(p, wbc, 1);
>>  		unlock_page(p);
>>  	}
>> @@ -3252,7 +3305,7 @@ int btree_write_cache_pages(struct address_space *mapping,
>>  {
>>  	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
>>  	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
>> -	struct extent_buffer *eb, *prev_eb = NULL;
>> +	struct extent_buffer *eb, *next, *prev_eb = NULL;
>>  	struct extent_page_data epd = {
>>  		.bio = NULL,
>>  		.tree = tree,
>> @@ -3326,17 +3379,41 @@ retry:
>>  				spin_unlock(&mapping->private_lock);
>>  				continue;
>>  			}
>> +			prev_eb = eb;
>> +
>> +next_eb:
>> +			next = eb->next;
>>  
>>  			ret = atomic_inc_not_zero(&eb->refs);
>> -			spin_unlock(&mapping->private_lock);
>> -			if (!ret)
>> -				continue;
>> +			if (eb->len >= PAGE_SIZE) {
>> +				spin_unlock(&mapping->private_lock);
>> +				if (!ret)
>> +					continue;
>> +			} else {
>> +				if (!ret)
>> +					goto inc_eb;
>> +				spin_unlock(&mapping->private_lock);
>> +
>> +				if (!test_bit(EXTENT_BUFFER_DIRTY,
>> +					      &eb->bflags)) {
>> +					spin_lock(&mapping->private_lock);
>> +					atomic_dec(&eb->refs);
>> +					ret = 0;
>> +					goto inc_eb;
>> +				}
>> +			}
>>  
>> -			prev_eb = eb;
>>  			ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
>>  			if (!ret) {
>> +				if (!(eb->len >= PAGE_SIZE))
>> +					spin_lock(&mapping->private_lock);
>> +
>>  				free_extent_buffer(eb);
>> -				continue;
>> +
>> +				if (eb->len >= PAGE_SIZE)
>> +					continue;
>> +				else
>> +					goto inc_eb;
>>  			}
>>  
>>  			ret = write_one_eb(eb, fs_info, wbc, &epd);
>> @@ -3345,8 +3422,26 @@ retry:
>>  				free_extent_buffer(eb);
>>  				break;
>>  			}
>> +
>> +			if (eb->len >= PAGE_SIZE) {
>> +				free_extent_buffer(eb);
>> +				goto written;
>> +			}
>> +
>> +			if (next)
>> +				spin_lock(&mapping->private_lock);
>>  			free_extent_buffer(eb);
>>  
>> +inc_eb:
>> +			if (!next) {
>> +				if (spin_is_locked(&mapping->private_lock))
>> +					spin_unlock(&mapping->private_lock);
>> +				goto written;
>> +			}
>> +			eb = next;
>> +			goto next_eb;
>> +
>> +written:
>>  			/*
>>  			 * the filesystem may choose to bump up nr_to_write.
>>  			 * We have to make sure to honor the new nr_to_write
>> @@ -4000,6 +4095,18 @@ static void __free_extent_buffer(struct extent_buffer *eb)
>>  	kmem_cache_free(extent_buffer_cache, eb);
>>  }
>>  
>> +/* Helper function to free extent buffers when there are multiple
>> + * extent buffers per page. */
>> +static void __free_extent_buffers(struct extent_buffer *eb)
>> +{
>> +	struct extent_buffer *next;
>> +
>> +	do {
>> +		next = eb->next;
>> +		__free_extent_buffer(eb);
>> +	} while ((eb = next));
>> +}
>> +
>>  static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>>  						   u64 start,
>>  						   unsigned long len,
>> @@ -4017,6 +4124,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>>  	eb->len = len;
>>  	eb->tree = tree;
>>  	eb->bflags = 0;
>> +	eb->next = NULL;
>>  	rwlock_init(&eb->lock);
>>  	atomic_set(&eb->write_locks, 0);
>>  	atomic_set(&eb->read_locks, 0);
>> @@ -4054,6 +4162,62 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
>>  	return eb;
>>  }
>>  
>> +/* Allocates an array of extent buffers for the specified page.
>> + * Should be called with the mapping's spin lock set. */
>> +static struct extent_buffer *__alloc_extent_buffers(struct extent_io_tree *tree,
>> +						    struct page *page,
>> +						    gfp_t mask)
>> +{
>> +	u32 blocksize_bits;
>> +	struct btrfs_inode *inode;
>> +	struct extent_buffer *eb_head;
>> +	struct extent_buffer *eb_cur;
>> +	u64 start;
>> +	unsigned long len;
>> +	int i;
>> +
>> +	/* Initialize variables. */
>> +	inode = BTRFS_I(tree->mapping->host);
>> +	blocksize_bits = inode->vfs_inode.i_sb->s_blocksize_bits;
>> +
>> +	/* Calculate extent buffer dimensions. */
>> +	start = page->index << PAGE_CACHE_SHIFT;
>> +	len = inode->root->leafsize;
>> +
>> +	/* Allocate the head extent buffer. */
>> +	eb_head = __alloc_extent_buffer(tree, start, len, GFP_NOFS);
>> +	if (!eb_head) {
>> +		WARN_ON(1);
>> +		return NULL;
>> +	}
>> +	start += len;
>> +	eb_head->pages[0] = page;
>> +	eb_cur = eb_head;
>> +
>> +	/* Allocate the other extent buffers. */
>> +	for (i = 1; i < (PAGE_CACHE_SIZE >> blocksize_bits); i++) {
>> +		eb_cur->next = __alloc_extent_buffer(tree, start, len,
>> +						     GFP_NOFS);
>> +		if (!eb_cur->next) {
>> +			WARN_ON(1);
>> +			goto free_ebs;
>> +		}
>> +		start += len;
>> +		eb_cur = eb_cur->next;
>> +		eb_cur->pages[0] = page;
>> +	}
>> +
>> +	/* Return the extent buffer head. */
>> +	return eb_head;
>> +
>> +free_ebs:
>> +	/* Free each extent buffer. */
>> +	// TODO: Implement.
>> +	pr_crit(KERN_CRIT "HACK: Need to implement this...\n");
>> +	WARN_ON(1);
>> +	return NULL;
>> +}
>> +
>>  struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
>>  {
>>  	unsigned long i;
>> @@ -4170,12 +4334,121 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
>>  }
>>  
>>  /*
>> + * Frees the page if all extent buffers belonging to the page are not
>> + * referernced. The extent buffers themselves must be free afterwards, too...
>> + * ret:	0 if the page did not need to be freed; 1 if the page was freed.
>> + */
>> +static int btrfs_release_extent_buffers_page(struct extent_buffer *eb,
>> +						struct extent_buffer **eb_head)
>> +{
>> +	struct extent_buffer *eb_cur;
>> +	struct extent_buffer *eb_temp;
>> +	struct page *page;
>> +	int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
>> +	int ret = 0;
>> +
>> +	if (extent_buffer_under_io(eb))
>> +		BUG_ON(1);
>> +
>> +	// ...is this even possible?
>> +	if (!num_extent_pages(eb->start, eb->len)) {
>> +		WARN_ON(1);
>> +		return ret;
>> +	}
>> +
>> +	page = extent_buffer_page(eb, 0);
>> +	if (page && mapped) {
>> +		spin_lock(&page->mapping->private_lock);
>> +		/*
>> +		 * We do this since we'll remove the pages after we've
>> +		 * removed the eb from the radix tree, so we could race
>> +		 * and have this page now attached to the new eb.  So
>> +		 * only clear page_private if it's still connected to
>> +		 * this eb.
>> +		 */
>> +		if (!PagePrivate(page)) {
>> +			spin_unlock(&page->mapping->private_lock);
>> +		} else {
>> +			/* Find the page eb corresponding to our eb. */
>> +			eb_cur = (struct extent_buffer *)page->private;
>> +			while (eb_cur->start != eb->start) {
>> +				eb_cur = eb_cur->next;
>> +				BUG_ON(!eb_cur);
>> +			}
>> +
>> +			/* See if a new eb has been attached to the page. */
>> +			if (eb_cur != eb) {
>> +				spin_unlock(&page->mapping->private_lock);
>> +				ret = 1;
>> +				goto page_release;
>> +			}
>> +
>> +			/* See if any other extent_buffer is using the page. */
>> +			eb_cur = (struct extent_buffer *)page->private;
>> +			do {
>> +				/* Check for any other references on the eb. */
>> +				spin_lock(&eb_cur->refs_lock);
>> +				if (!atomic_dec_and_test(&eb_cur->refs)) {
>> +					atomic_inc(&eb_cur->refs);
>> +					spin_unlock(&eb_cur->refs_lock);
>> +					eb_temp = eb_cur;
>> +					eb_cur = (struct extent_buffer *)
>> +						 page->private;
>> +					while (eb_cur != eb_temp) {
>> +						atomic_inc(&eb_cur->refs);
>> +						eb_cur = eb_cur->next;
>> +					}
>> +					spin_unlock(
>> +						&page->mapping->private_lock);
>> +					goto page_release;
>> +				}
>> +				spin_unlock(&eb_cur->refs_lock);
>> +			} while ((eb_cur = eb_cur->next) != NULL);
>> +
>> +			/* Sanity checks. */
>> +			eb_cur = (struct extent_buffer *)page->private;
>> +			do {
>> +				BUG_ON(extent_buffer_under_io(eb_cur));
>> +			} while ((eb_cur = eb_cur->next) != NULL);
>> +			BUG_ON(PageDirty(page));
>> +			BUG_ON(PageWriteback(page));
>> +			/*
>> +			 * We need to make sure we haven't been attached
>> +			 * to a new eb.
>> +			 */
>> +			eb_cur = (struct extent_buffer *)page->private;
>> +			*eb_head = eb_cur;
>> +			eb_temp = NULL;
>> +			ClearPagePrivate(page);
>> +			set_page_private(page, 0);
>> +			/* One for the page private. */
>> +			page_cache_release(page);
>> +			ret = 1;
>> +			spin_unlock(&page->mapping->private_lock);
>> +		}
>> +	}
>> +
>> +page_release:
>> +	if (page) {
>> +		/* One for when we alloced the page */
>> +		page_cache_release(page);
>> +	}
>> +	return ret;
>> +}
>> +
>> +/*
>>   * Helper for releasing the extent buffer.
>>   */
>>  static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
>>  {
>> -	btrfs_release_extent_buffer_page(eb, 0);
>> -	__free_extent_buffer(eb);
>> +	if (eb->len >= PAGE_SIZE) {
>> +		btrfs_release_extent_buffer_page(eb, 0);
>> +		__free_extent_buffer(eb);
>> +	} else {
>> +		struct extent_buffer *eb_head;
>> +		if (btrfs_release_extent_buffers_page(eb, &eb_head))
>> +			__free_extent_buffers(eb_head);
>> +	}
>>  }
>>  
>>  static void check_buffer_tree_ref(struct extent_buffer *eb)
>> @@ -4222,16 +4495,153 @@ static void mark_extent_buffer_accessed(struct extent_buffer *eb)
>>  struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
>>  					  u64 start, unsigned long len)
>>  {
>> -	unsigned long num_pages = num_extent_pages(start, len);
>> -	unsigned long i;
>> -	unsigned long index = start >> PAGE_CACHE_SHIFT;
>> +	/* Allocate a new extent_buffer depending on blocksize*/
>> +	if (len < PAGE_CACHE_SIZE)
>> +		return alloc_extent_buffer_multiple(tree, start, len);
>> +	return alloc_extent_buffer_single(tree, start, len);
>> +}
>> +
>> +struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
>> +						   u64 start,
>> +						   unsigned long len) {
>> +
>> +	struct address_space *mapping;
>> +	u32 blocksize_bits;
>> +	struct btrfs_inode *btrfs_inode;
>> +	struct extent_buffer *eb_cur;
>> +	struct extent_buffer *eb_head;
>> +	struct extent_buffer *exists;
>> +	unsigned long index;
>> +	struct page *page;
>> +	int ret;
>> +
>> +	/* Initialize variables. */
>> +	btrfs_inode = BTRFS_I(tree->mapping->host);
>> +	blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
>> +
>> +	/* Sanity checks. */
>> +	WARN_ON(num_extent_pages(start, len) > 1);
>> +
>> +	/* See if the extent_buffer already exists in the radix tree. */
>> +	rcu_read_lock();
>> +	eb_cur = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
>> +	if (eb_cur && atomic_inc_not_zero(&eb_cur->refs)) {
>> +		rcu_read_unlock();
>> +		mark_extent_buffer_accessed(eb_cur);
>> +		return eb_cur;
>> +	}
>> +	rcu_read_unlock();
>> +
>> +	/* Find the page in the mapping. */
>> +	index = start >> PAGE_CACHE_SHIFT;
>> +	mapping = tree->mapping;
>> +	page = find_or_create_page(mapping, index, GFP_NOFS);
>> +	if (!page) {
>> +		WARN_ON(1);
>> +		return NULL;
>> +	}
>> +
>> +	/* Allocate each extent buffer for the page. */
>> +	eb_head = __alloc_extent_buffers(tree, page, GFP_NOFS);
>> +	if (!eb_head) {
>> +		WARN_ON(1);
>> +		return NULL;
>> +	}
>> +
>> +	/* See if extent buffers have already been allocated for
>> +	 * this page. */
>> +	spin_lock(&mapping->private_lock);
>> +	if (PagePrivate(page)) {
>> +		/*
>> +		 * We could have already allocated an eb for this page
>> +		 * and attached one so lets see if we can get a ref on
>> +		 * the existing eb, and if we can we know it's good and
>> +		 * we can just return that one, else we know we can just
>> +		 * overwrite page->private.
>> +		 */
>> +		eb_cur = (struct extent_buffer *)page->private;
>> +		while (eb_cur->start != start) {
>> +			eb_cur = eb_cur->next;
>> +			BUG_ON(!eb_cur);
>> +		}
>> +		check_buffer_tree_ref(eb_cur);
>> +		spin_unlock(&mapping->private_lock);
>> +		unlock_page(page);
>> +		mark_extent_buffer_accessed(eb_cur);
>> +		__free_extent_buffers(eb_head);
>> +		return eb_cur;
>> +	}
>> +
>> +	/* Bind the extent buffer to the page. */
>> +	attach_extent_buffer_page(eb_head, page);
>> +	spin_unlock(&mapping->private_lock);
>> +	WARN_ON(PageDirty(page));
>> +	mark_page_accessed(page);
>> +
>> +again:
>> +	/* Set eb_cur to the buffer added. */
>> +	eb_cur = eb_head;
>> +	while (start != eb_cur->start) {
>> +		eb_cur = eb_cur->next;
>> +		BUG_ON(!eb_cur);
>> +	}
>> +
>> +	/* Preload the radix tree. */
>> +	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
>> +	if (ret) {
>> +		WARN_ON(1);
>> +		return NULL;
>> +	}
>> +
>> +	/* Add the extent buffer to the radix tree. */
>> +	spin_lock(&tree->buffer_lock);
>> +	ret = radix_tree_insert(&tree->buffer,
>> +				eb_cur->start >> blocksize_bits,
>> +				eb_cur);
>> +	if (ret == -EEXIST) {
>> +		exists = radix_tree_lookup(&tree->buffer,
>> +				eb_cur->start >> blocksize_bits);
>> +		if (exists->start != start)
>> +			BUG_ON(1);
>> +		if (!atomic_inc_not_zero(&exists->refs)) {
>> +			spin_unlock(&tree->buffer_lock);
>> +			radix_tree_preload_end();
>> +			exists = NULL;
>> +			goto again;
>> +		}
>> +		spin_unlock(&tree->buffer_lock);
>> +		radix_tree_preload_end();
>> +		mark_extent_buffer_accessed(exists);
>> +		WARN_ON(!atomic_dec_and_test(&eb_cur->refs));
>> +		btrfs_release_extent_buffer(eb_cur);
>> +		return exists;
>> +	}
>> +
>> +	/* Set the extent buffer's tree-reference bits. */
>> +	check_buffer_tree_ref(eb_cur);
>> +	spin_unlock(&tree->buffer_lock);
>> +	radix_tree_preload_end();
>> +
>> +	/* Not quite sure what this does. */
>> +	SetPageChecked(eb_head->pages[0]);
>> +	unlock_page(eb_head->pages[0]);
>> +
>> +	return eb_cur;
>> +}
>> +
>> +struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
>> +						 u64 start, unsigned long len) {
>> +	struct address_space *mapping = tree->mapping;
>>  	struct extent_buffer *eb;
>>  	struct extent_buffer *exists = NULL;
>> +	unsigned long i;
>> +	unsigned long index = start >> PAGE_CACHE_SHIFT;
>> +	unsigned long num_pages = num_extent_pages(start, len);
>>  	struct page *p;
>> -	struct address_space *mapping = tree->mapping;
>>  	int uptodate = 1;
>>  	int ret;
>>  
>> +	/* See if the extent_buffer already exists */
>>  	rcu_read_lock();
>>  	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
>>  	if (eb && atomic_inc_not_zero(&eb->refs)) {
>> @@ -4350,9 +4760,17 @@ struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
>>  					 u64 start, unsigned long len)
>>  {
>>  	struct extent_buffer *eb;
>> +	struct btrfs_inode *btrfs_inode = BTRFS_I(tree->mapping->host);
>> +	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
>>  
>>  	rcu_read_lock();
>> -	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
>> +	// This branch needs to be fixed when the allocation code is merged.
>> +	// Seriously.
>> +	if (blocksize_bits >= PAGE_CACHE_SHIFT)
>> +		eb = radix_tree_lookup(&tree->buffer,
>> +				       start >> PAGE_CACHE_SHIFT);
>> +	else
>> +		eb = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
>>  	if (eb && atomic_inc_not_zero(&eb->refs)) {
>>  		rcu_read_unlock();
>>  		mark_extent_buffer_accessed(eb);
>> @@ -4371,9 +4789,25 @@ static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
>>  	__free_extent_buffer(eb);
>>  }
>>  
>> -/* Expects to have eb->eb_lock already held */
>> +/*
>> + * The RCU head must point to the first extent buffer belonging to a page.
>> + */
>> +static inline void btrfs_release_extent_buffers_rcu(struct rcu_head *head)
>> +{
>> +	struct extent_buffer *eb =
>> +			container_of(head, struct extent_buffer, rcu_head);
>> +
>> +	do {
>> +		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
>> +	} while ((eb = eb->next));
>> +}
>> +
>> +/* Expects to have eb->refs_lock already held */
>>  static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
>>  {
>> +	struct btrfs_inode *btrfs_inode = BTRFS_I(eb->tree->mapping->host);
>> +	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
>> +
>>  	WARN_ON(atomic_read(&eb->refs) == 0);
>>  	if (atomic_dec_and_test(&eb->refs)) {
>>  		if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
>> @@ -4381,17 +4815,35 @@ static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
>>  		} else {
>>  			struct extent_io_tree *tree = eb->tree;
>>  
>> +			/* Dumb hack to make releasing the page easier. */
>> +			if (eb->len < PAGE_SIZE)
>> +				atomic_inc(&eb->refs);
>> +
>>  			spin_unlock(&eb->refs_lock);
>>  
>> +			// This also needs to be fixed when allocation code is
>> +			// merged.
>>  			spin_lock(&tree->buffer_lock);
>> -			radix_tree_delete(&tree->buffer,
>> -					  eb->start >> PAGE_CACHE_SHIFT);
>> +			if (eb->len >= PAGE_SIZE)
>> +				radix_tree_delete(&tree->buffer,
>> +					  eb->start >> blocksize_bits);
>> +			else
>> +				radix_tree_delete(&tree->buffer,
>> +					  eb->start >> blocksize_bits);
>>  			spin_unlock(&tree->buffer_lock);
>>  		}
>>  
>>  		/* Should be safe to release our pages at this point */
>> -		btrfs_release_extent_buffer_page(eb, 0);
>> -		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
>> +		if (eb->len >= PAGE_SIZE) {
>> +			btrfs_release_extent_buffer_page(eb, 0);
>> +			call_rcu(&eb->rcu_head,
>> +				 btrfs_release_extent_buffer_rcu);
>> +		} else {
>> +			struct extent_buffer *eb_head;
>> +			if (btrfs_release_extent_buffers_page(eb, &eb_head))
>> +				btrfs_release_extent_buffers_rcu(
>> +							&eb_head->rcu_head);
>> +		}
>>  		return 1;
>>  	}
>>  	spin_unlock(&eb->refs_lock);
>> @@ -4482,6 +4934,11 @@ int set_extent_buffer_dirty(struct extent_buffer *eb)
>>  
>>  	for (i = 0; i < num_pages; i++)
>>  		set_page_dirty(extent_buffer_page(eb, i));
>> +	/* Run an additional sanity check here instead of
>> +	 * in btree_set_page_dirty() since we can't get the eb there for
>> +	 * subpage blocksize. */
>> +	if (eb->len < PAGE_SIZE)
>> +		btrfs_assert_tree_locked(eb);
>>  	return was_dirty;
>>  }
>>  
>> @@ -4503,11 +4960,14 @@ int clear_extent_buffer_uptodate(struct extent_buffer *eb)
>>  	unsigned long num_pages;
>>  
>>  	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
>> -	num_pages = num_extent_pages(eb->start, eb->len);
>> -	for (i = 0; i < num_pages; i++) {
>> -		page = extent_buffer_page(eb, i);
>> -		if (page)
>> -			ClearPageUptodate(page);
>> +	/* Ignore the page's uptodate flag forsubpage blocksize. */
>> +	if (eb->len >= PAGE_SIZE) {
>> +		num_pages = num_extent_pages(eb->start, eb->len);
>> +		for (i = 0; i < num_pages; i++) {
>> +			page = extent_buffer_page(eb, i);
>> +			if (page)
>> +				ClearPageUptodate(page);
>> +		}
>>  	}
>>  	return 0;
>>  }
>> @@ -4518,11 +4978,16 @@ int set_extent_buffer_uptodate(struct extent_buffer *eb)
>>  	struct page *page;
>>  	unsigned long num_pages;
>>  
>> +	/* Set extent buffer up-to-date. */
>>  	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
>> -	num_pages = num_extent_pages(eb->start, eb->len);
>> -	for (i = 0; i < num_pages; i++) {
>> -		page = extent_buffer_page(eb, i);
>> -		SetPageUptodate(page);
>> +
>> +	/* Set pages up-to-date. */
>> +	if (eb->len >= PAGE_CACHE_SIZE) {
>> +		num_pages = num_extent_pages(eb->start, eb->len);
>> +		for (i = 0; i < num_pages; i++) {
>> +			page = extent_buffer_page(eb, i);
>> +			SetPageUptodate(page);
>> +		}
>>  	}
>>  	return 0;
>>  }
>> @@ -4606,7 +5071,7 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
>>  		}
>>  	}
>>  	if (all_uptodate) {
>> -		if (start_i == 0)
>> +		if (start_i == 0 && eb->len >= PAGE_SIZE)
>>  			set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
>>  		goto unlock_exit;
>>  	}
>> @@ -4693,7 +5158,7 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>>  			       unsigned long *map_start,
>>  			       unsigned long *map_len)
>>  {
>> -	size_t offset = start & (PAGE_CACHE_SIZE - 1);
>> +	size_t offset;
>>  	char *kaddr;
>>  	struct page *p;
>>  	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
>> @@ -4709,6 +5174,9 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>>  		*map_start = 0;
>>  	} else {
>>  		offset = 0;
>> +		// I'm pretty sure that this is a) just plain wrong and
>> +		// b) will never realistically execute; not entirely sure,
>> +		// though...
>>  		*map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
>>  	}
>>  
>> @@ -4722,7 +5190,7 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>>  	p = extent_buffer_page(eb, i);
>>  	kaddr = page_address(p);
>>  	*map = kaddr + offset;
>> -	*map_len = PAGE_CACHE_SIZE - offset;
>> +	*map_len = (PAGE_CACHE_SIZE - offset) & (eb->len - 1);
>>  	return 0;
>>  }
>>  
>> @@ -4996,6 +5464,7 @@ void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
>>  int try_release_extent_buffer(struct page *page, gfp_t mask)
>>  {
>>  	struct extent_buffer *eb;
>> +	int ret;
>>  
>>  	/*
>>  	 * We need to make sure noboody is attaching this page to an eb right
>> @@ -5010,30 +5479,61 @@ int try_release_extent_buffer(struct page *page, gfp_t mask)
>>  	eb = (struct extent_buffer *)page->private;
>>  	BUG_ON(!eb);
>>  
>> -	/*
>> -	 * This is a little awful but should be ok, we need to make sure that
>> -	 * the eb doesn't disappear out from under us while we're looking at
>> -	 * this page.
>> -	 */
>> -	spin_lock(&eb->refs_lock);
>> -	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
>> -		spin_unlock(&eb->refs_lock);
>> +	if (eb->len >= PAGE_SIZE) {
>> +		/*
>> +		 * This is a little awful but should be ok, we need to make
>> +		 * sure that the eb doesn't disappear out from under us while
>> +		 * we're looking at this page.
>> +		 */
>> +		spin_lock(&eb->refs_lock);
>> +		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
>> +			spin_unlock(&eb->refs_lock);
>> +			spin_unlock(&page->mapping->private_lock);
>> +			return 0;
>> +		}
>>  		spin_unlock(&page->mapping->private_lock);
>> -		return 0;
>> -	}
>> -	spin_unlock(&page->mapping->private_lock);
>>  
>> -	if ((mask & GFP_NOFS) == GFP_NOFS)
>> -		mask = GFP_NOFS;
>> +		if ((mask & GFP_NOFS) == GFP_NOFS)
>> +			mask = GFP_NOFS;
>>  
>> -	/*
>> -	 * If tree ref isn't set then we know the ref on this eb is a real ref,
>> -	 * so just return, this page will likely be freed soon anyway.
>> -	 */
>> -	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
>> -		spin_unlock(&eb->refs_lock);
>> -		return 0;
>> -	}
>> +		/*
>> +		 * If tree ref isn't set then we know the ref on this eb is a
>> +		 * real ref, so just return, this page will likely be freed
>> +		 * soon anyway.
>> +		 */
>> +		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
>> +			spin_unlock(&eb->refs_lock);
>> +			return 0;
>> +		}
>>  
>> -	return release_extent_buffer(eb, mask);
>> +		return release_extent_buffer(eb, mask);
>> +	} else {
>> +		ret = 0;
>> +		do {
>> +			spin_lock(&eb->refs_lock);
>> +			if (atomic_read(&eb->refs) != 1 ||
>> +					extent_buffer_under_io(eb)) {
>> +				spin_unlock(&eb->refs_lock);
>> +				continue;
>> +			}
>> +			spin_unlock(&page->mapping->private_lock);
>> +
>> +			if ((mask & GFP_NOFS) == GFP_NOFS)
>> +				mask = GFP_NOFS;
>> +
>> +			if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF,
>> +						&eb->bflags)) {
>> +				spin_unlock(&eb->refs_lock);
>> +				spin_lock(&page->mapping->private_lock);
>> +				continue;
>> +			}
>> +
>> +			/* No idea what to do with the 'ret' here. */
>> +			ret |= release_extent_buffer(eb, mask);
>> +
>> +			spin_lock(&page->mapping->private_lock);
>> +		} while ((eb = eb->next) != NULL);
>> +		spin_unlock(&page->mapping->private_lock);
>> +		return ret;
>> +	}
>>  }
>> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
>> index 2eacfab..955ef5e 100644
>> --- a/fs/btrfs/extent_io.h
>> +++ b/fs/btrfs/extent_io.h
>> @@ -163,6 +163,9 @@ struct extent_buffer {
>>  	wait_queue_head_t lock_wq;
>>  	struct page *inline_pages[INLINE_EXTENT_BUFFER_PAGES];
>>  	struct page **pages;
>> +
>> +	/* Acyclic linked list of extent_buffers belonging to a single page. */
>> +	struct extent_buffer *next;
>>  };
>>  
>>  static inline void extent_set_compress_type(unsigned long *bio_flags,
>> @@ -270,6 +273,10 @@ void set_page_extent_mapped(struct page *page);
>>  
>>  struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
>>  					  u64 start, unsigned long len);
>> +struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
>> +						 u64 start, unsigned long len);
>> +struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
>> +						 u64 start, unsigned long len);
>>  struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len);
>>  struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
>>  struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index 3bff4d4..8745289 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -1340,7 +1340,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>>  		}
>>  
>>  		ret = btrfs_delalloc_reserve_space(inode,
>> -					num_pages << PAGE_CACHE_SHIFT);
>> +					write_bytes);
>>  		if (ret)
>>  			break;
>>  
>> @@ -1354,7 +1354,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>>  				    force_page_uptodate);
>>  		if (ret) {
>>  			btrfs_delalloc_release_space(inode,
>> -					num_pages << PAGE_CACHE_SHIFT);
>> +					write_bytes);
>>  			break;
>>  		}
>>  
>> @@ -1392,8 +1392,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>>  				spin_unlock(&BTRFS_I(inode)->lock);
>>  			}
>>  			btrfs_delalloc_release_space(inode,
>> -					(num_pages - dirty_pages) <<
>> -					PAGE_CACHE_SHIFT);
>> +						write_bytes - copied);
>>  		}
>>  
>>  		if (copied > 0) {
>> @@ -1402,7 +1401,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
>>  						NULL);
>>  			if (ret) {
>>  				btrfs_delalloc_release_space(inode,
>> -					dirty_pages << PAGE_CACHE_SHIFT);
>> +						copied);
>>  				btrfs_drop_pages(pages, num_pages);
>>  				break;
>>  			}
>> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
>> index 59ea2e4..1c0e254 100644
>> --- a/fs/btrfs/free-space-cache.c
>> +++ b/fs/btrfs/free-space-cache.c
>> @@ -960,6 +960,8 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
>>  
>>  	if (block_group)
>>  		start = block_group->key.objectid;
>> +	else // Hmm I don't recall putting this here.
>> +		start = (u64)-1;
>>  
>>  	while (block_group && (start < block_group->key.objectid +
>>  			       block_group->key.offset)) {
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index 3368c10..11ff3dd 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -2040,22 +2040,38 @@ static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
>>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>>  	struct btrfs_ordered_extent *ordered_extent = NULL;
>>  	struct btrfs_workers *workers;
>> +	u64 block_size = 1 << inode->i_blkbits;
>> +	u64 io_size;
>> +
>> +	if (block_size >= PAGE_CACHE_SIZE)
>> +		io_size = end - start + 1;
>> +	else
>> +		io_size = block_size;
>>  
>>  	trace_btrfs_writepage_end_io_hook(page, start, end, uptodate);
>>  
>>  	ClearPagePrivate2(page);
>> -	if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
>> -					    end - start + 1, uptodate))
>> -		return 0;
>> -
>> -	ordered_extent->work.func = finish_ordered_fn;
>> -	ordered_extent->work.flags = 0;
>> -
>> -	if (btrfs_is_free_space_inode(inode))
>> -		workers = &root->fs_info->endio_freespace_worker;
>> -	else
>> -		workers = &root->fs_info->endio_write_workers;
>> -	btrfs_queue_worker(workers, &ordered_extent->work);
>> +next_block:
>> +	if (btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
>> +					    io_size, uptodate)) {
>> +		ordered_extent->work.func = finish_ordered_fn;
>> +		ordered_extent->work.flags = 0;
>> +
>> +		if (btrfs_is_free_space_inode(inode))
>> +			workers = &root->fs_info->endio_freespace_worker;
>> +		else
>> +			workers = &root->fs_info->endio_write_workers;
>> +		btrfs_queue_worker(workers, &ordered_extent->work);
>> +	}
>> +
>> +	// I think that writes are always block-size granularity.
>> +	if (block_size < PAGE_CACHE_SIZE)
>> +		BUG_ON(start & (io_size - 1)); // Welp, one way to make sure...
>> +	start += io_size;
>> +	if (start < end)
>> +		goto next_block;
>> +	// We overshot. I'm pretty sure that this is terrible.
>> +	BUG_ON(start != (end + 1));
>>  
>>  	return 0;
>>  }
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 657d83c..c0269df 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -3937,8 +3937,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>>  		return btrfs_ioctl_qgroup_create(file, argp);
>>  	case BTRFS_IOC_QGROUP_LIMIT:
>>  		return btrfs_ioctl_qgroup_limit(file, argp);
>> -	case BTRFS_IOC_DEV_REPLACE:
>> -		return btrfs_ioctl_dev_replace(root, argp);
>> +	//case BTRFS_IOC_DEV_REPLACE:
>> +//		return btrfs_ioctl_dev_replace(root, argp);
>>  	}
>>  
>>  	return -ENOTTY;
>> -- 
>> 1.7.1
>>
>> --
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[e-mail] Dec. 18, 2012, 10:26 p.m. UTC | #3

On 12/18/2012 12:49 AM, Miao Xie wrote:

> On tue, 18 Dec 2012 15:30:51 +0800, Liu Bo wrote:
>> On Mon, Dec 17, 2012 at 11:13:25PM -0800, [e-mail] wrote:
>>> From: Wade Cline<[e-mail]>
>>>
>>> v1 ->  v2:
>>> - Added Signed-off-by tag (it's kind of important).
>>>
>>> This patch is only an RFC. My internship is ending and I was hoping
>>> to get some feedback and incorporate any suggestions people may
>>> have before my internship ends along with life as we know it (this
>>> Friday).
>>>
>>> The filesystem should mount/umount properly but tends towards the
>>> explosive side when writes start happening. My current focus is on
>>> checksumming issues and also an error when releasing extent buffers
>>> when creating a large file with 'dd'... and probably any other
>>> method. There's still a significant amount of work that needs to be
>>> done before this should be incorporated into mainline.
>>>
>>> A couple of notes:
>>>      - Based off of Josef's btrfs-next branch, commit
>>>        8d089a86e45b34d7bc534d955e9d8543609f7e42
>>>      - C99-style comments are "meta-comments" where I'd like more
>>>        feedback; they aren't permanent but make 'checkpatch' moan.
>>>      - extent_buffer allocation and freeing need their code paths
>>>        merged; they're currently in separate functions and are both
>>>        very ugly.
>>>      - The patch itself will eventually need to be broken down
>>>        into smaller pieces if at all possible...
>>
>> Could you please first elaborate why we need this subpagesize stuff and
>> any user case in this patch's commit log?
>> Or Am I missing something?
>
> It is used on the machines on which the page size is larger than 4KB (Such as powerpc)
>
> Thanks
> Miao

Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
then that filesystem is incompatible with architectures such as PowerPC
and MIPS which have a page size larger than 4k.

-Wade

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Chris Samuel Dec. 18, 2012, 11:01 p.m. UTC | #4

On 19/12/12 09:26, Wade Cline wrote:

> Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
> then that filesystem is incompatible with architectures such as PowerPC
> and MIPS which have a page size larger than 4k.

What happens currently?    Does the btrfs code detect the mismatch and
refuse to mount, or does it all go horribly wrong?

cheers,
Chris

[e-mail] Dec. 18, 2012, 11:19 p.m. UTC | #5

On 12/18/2012 03:01 PM, Chris Samuel wrote:

> On 19/12/12 09:26, Wade Cline wrote:
>
>> Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
>> then that filesystem is incompatible with architectures such as PowerPC
>> and MIPS which have a page size larger than 4k.
> What happens currently?    Does the btrfs code detect the mismatch and
> refuse to mount, or does it all go horribly wrong?
>
> cheers,
> Chris
I recall hacking the mkfs.btrfs tool, testing it, and finding that the
filesystem wouldn't mount. I haven't created a non-hacked filesystem
on x86 and ported it to PPC verbatim yet, but the same should happen
there; it shouldn't crash the kernel.

-Wade

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Liu Bo Dec. 19, 2012, 2:02 a.m. UTC | #6

On Tue, Dec 18, 2012 at 02:26:50PM -0800, Wade Cline wrote:
> On 12/18/2012 12:49 AM, Miao Xie wrote:
> 
> >On tue, 18 Dec 2012 15:30:51 +0800, Liu Bo wrote:
> >>On Mon, Dec 17, 2012 at 11:13:25PM -0800, [e-mail] wrote:
> >>>From: Wade Cline<[e-mail]>
> >>>
> >>>v1 ->  v2:
> >>>- Added Signed-off-by tag (it's kind of important).
> >>>
> >>>This patch is only an RFC. My internship is ending and I was hoping
> >>>to get some feedback and incorporate any suggestions people may
> >>>have before my internship ends along with life as we know it (this
> >>>Friday).
> >>>
> >>>The filesystem should mount/umount properly but tends towards the
> >>>explosive side when writes start happening. My current focus is on
> >>>checksumming issues and also an error when releasing extent buffers
> >>>when creating a large file with 'dd'... and probably any other
> >>>method. There's still a significant amount of work that needs to be
> >>>done before this should be incorporated into mainline.
> >>>
> >>>A couple of notes:
> >>>     - Based off of Josef's btrfs-next branch, commit
> >>>       8d089a86e45b34d7bc534d955e9d8543609f7e42
> >>>     - C99-style comments are "meta-comments" where I'd like more
> >>>       feedback; they aren't permanent but make 'checkpatch' moan.
> >>>     - extent_buffer allocation and freeing need their code paths
> >>>       merged; they're currently in separate functions and are both
> >>>       very ugly.
> >>>     - The patch itself will eventually need to be broken down
> >>>       into smaller pieces if at all possible...
> >>
> >>Could you please first elaborate why we need this subpagesize stuff and
> >>any user case in this patch's commit log?
> >>Or Am I missing something?
> >
> >It is used on the machines on which the page size is larger than 4KB (Such as powerpc)
> >
> >Thanks
> >Miao
> 
> Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
> then that filesystem is incompatible with architectures such as PowerPC
> and MIPS which have a page size larger than 4k.
> 
> -Wade
> 

I'm just saying there _should_ be some kind of such description about
the patch in your commit log...

That's for those who don't ever know the background of the idea.

thanks,
liubo
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[e-mail] Dec. 19, 2012, 2:29 a.m. UTC | #7

On 12/18/2012 06:02 PM, Liu Bo wrote:

> On Tue, Dec 18, 2012 at 02:26:50PM -0800, Wade Cline wrote:
>> On 12/18/2012 12:49 AM, Miao Xie wrote:
>>
>>> On tue, 18 Dec 2012 15:30:51 +0800, Liu Bo wrote:
>>>> On Mon, Dec 17, 2012 at 11:13:25PM -0800, [e-mail] wrote:
>>>>> From: Wade Cline<[e-mail]>
>>>>>
>>>>> v1 ->   v2:
>>>>> - Added Signed-off-by tag (it's kind of important).
>>>>>
>>>>> This patch is only an RFC. My internship is ending and I was hoping
>>>>> to get some feedback and incorporate any suggestions people may
>>>>> have before my internship ends along with life as we know it (this
>>>>> Friday).
>>>>>
>>>>> The filesystem should mount/umount properly but tends towards the
>>>>> explosive side when writes start happening. My current focus is on
>>>>> checksumming issues and also an error when releasing extent buffers
>>>>> when creating a large file with 'dd'... and probably any other
>>>>> method. There's still a significant amount of work that needs to be
>>>>> done before this should be incorporated into mainline.
>>>>>
>>>>> A couple of notes:
>>>>>      - Based off of Josef's btrfs-next branch, commit
>>>>>        8d089a86e45b34d7bc534d955e9d8543609f7e42
>>>>>      - C99-style comments are "meta-comments" where I'd like more
>>>>>        feedback; they aren't permanent but make 'checkpatch' moan.
>>>>>      - extent_buffer allocation and freeing need their code paths
>>>>>        merged; they're currently in separate functions and are both
>>>>>        very ugly.
>>>>>      - The patch itself will eventually need to be broken down
>>>>>        into smaller pieces if at all possible...
>>>>
>>>> Could you please first elaborate why we need this subpagesize stuff and
>>>> any user case in this patch's commit log?
>>>> Or Am I missing something?
>>>
>>> It is used on the machines on which the page size is larger than 4KB (Such as powerpc)
>>>
>>> Thanks
>>> Miao
>>
>> Yeah. Basically, if we create a btrfs filesystem with a 4k blocksize
>> then that filesystem is incompatible with architectures such as PowerPC
>> and MIPS which have a page size larger than 4k.
>>
>> -Wade
>>
>
> I'm just saying there _should_ be some kind of such description about
> the patch in your commit log...
>
> That's for those who don't ever know the background of the idea.
>
> thanks,
> liubo
>

Okay, I'll make sure to add that description next time I send the
patch out.

Thanks,
Wade

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Patch

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index fbaaf20..c786a58 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1938,14 +1938,19 @@  static inline void btrfs_set_token_##name(struct extent_buffer *eb,	\
 #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)		\
 static inline u##bits btrfs_##name(struct extent_buffer *eb)		\
 {									\
-	type *p = page_address(eb->pages[0]);				\
-	u##bits res = le##bits##_to_cpu(p->member);			\
+	type *p;							\
+	u##bits res;							\
+									\
+	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
+	res = le##bits##_to_cpu(p->member);				\
 	return res;							\
 }									\
 static inline void btrfs_set_##name(struct extent_buffer *eb,		\
 				    u##bits val)			\
 {									\
-	type *p = page_address(eb->pages[0]);				\
+	type *p;							\
+									\
+	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
 	p->member = cpu_to_le##bits(val);				\
 }
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f633af8..00b80b7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -373,6 +373,24 @@  static int btree_read_extent_buffer_pages(struct btrfs_root *root,
 					       WAIT_COMPLETE,
 					       btree_get_extent, mirror_num);
 		if (!ret) {
+			/*
+			 * I think that this is bad and should be moved
+			 * into btree_readpage_end_io_hook(), but that
+			 * it should apply to a single block at a time.
+			 * That may be difficult and would make the
+			 * function name a misnomer, but mostly I hate
+			 * the silly goto.
+			 */
+			if (eb->len < PAGE_SIZE &&
+			    !extent_buffer_uptodate(eb)) {
+				if (csum_tree_block(root, eb, 1)) {
+					ret = -EIO;
+					goto bad;
+				} else {
+					set_extent_buffer_uptodate(eb);
+				}
+			}
+
 			if (!verify_parent_transid(io_tree, eb,
 						   parent_transid, 0))
 				break;
@@ -385,6 +403,7 @@  static int btree_read_extent_buffer_pages(struct btrfs_root *root,
 		 * there is no reason to read the other copies, they won't be
 		 * any less wrong.
 		 */
+bad:
 		if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
 			break;
 
@@ -416,29 +435,55 @@  static int btree_read_extent_buffer_pages(struct btrfs_root *root,
  * checksum a dirty tree block before IO.  This has extra checks to make sure
  * we only fill in the checksum field in the first page of a multi-page block
  */
-
-static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
+static int csum_dirty_buffer(struct btrfs_root *root, struct page *page,
+			     unsigned int offset, unsigned int len)
 {
-	struct extent_io_tree *tree;
 	u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
 	u64 found_start;
 	struct extent_buffer *eb;
 
-	tree = &BTRFS_I(page->mapping->host)->io_tree;
+	if (!PageUptodate(page)) {
+		WARN_ON(1);
+		return 0;
+	}
 
 	eb = (struct extent_buffer *)page->private;
-	if (page != eb->pages[0])
-		return 0;
+	if (eb->len >= PAGE_SIZE) {
+		if (eb->pages[0] != page)
+			return 0;
+	} else {
+		start += offset;
+		while (eb->start != start) {
+			eb = eb->next;
+			BUG_ON(!eb);
+		}
+next:
+		if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+			WARN_ON(1);
+		if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
+			WARN_ON(1);
+		if (eb->pages[0] != page)
+			WARN_ON(1);
+	}
+
 	found_start = btrfs_header_bytenr(eb);
 	if (found_start != start) {
 		WARN_ON(1);
 		return 0;
 	}
-	if (!PageUptodate(page)) {
-		WARN_ON(1);
-		return 0;
-	}
+
 	csum_tree_block(root, eb, 0);
+
+	if (eb->len < PAGE_SIZE) {
+		len -= eb->len;
+		BUG_ON(len & (eb->len - 1));
+		if (len) {
+			start += eb->len;
+			eb = eb->next;
+			goto next;
+		}
+	}
+
 	return 0;
 }
 
@@ -579,6 +624,19 @@  static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
 
 	tree = &BTRFS_I(page->mapping->host)->io_tree;
 	eb = (struct extent_buffer *)page->private;
+	if (eb->len < PAGE_SIZE) {
+		/* Find the eb that tried to submit a read request. This is
+		 * a little bit funky. */
+		do {
+			if (!atomic_read(&eb->io_pages))
+				continue;
+			if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags) ||
+			    test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+				continue;
+			break;
+		} while ((eb = eb->next));
+		BUG_ON(!eb);
+	}
 
 	/* the pending IO might have been the only thing that kept this buffer
 	 * in memory.  Make sure we have a ref for all this other checks
@@ -615,8 +673,11 @@  static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
 	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb),
 				       eb, found_level);
 
-	ret = csum_tree_block(root, eb, 1);
-	if (ret) {
+	/*
+	 * Subpagesize blocksize checksumming is currently done in
+	 * btree_read_extent_buffer_pages().
+	 */
+	if (eb->len >= PAGE_SIZE && csum_tree_block(root, eb, 1)) {
 		ret = -EIO;
 		goto err;
 	}
@@ -631,8 +692,15 @@  static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
 		ret = -EIO;
 	}
 
-	if (!ret)
+	/*
+	 * For subpagesize blocksize, only the page needs to be set
+	 * up-to-date; each extent_buffer is set up-to-date when it is
+	 * checksummed.
+	 */
+	if (eb->len >= PAGE_SIZE)
 		set_extent_buffer_uptodate(eb);
+	else
+		SetPageUptodate(eb->pages[0]);
 err:
 	if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
 		clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
@@ -828,7 +896,8 @@  static int btree_csum_one_bio(struct bio *bio)
 	WARN_ON(bio->bi_vcnt <= 0);
 	while (bio_index < bio->bi_vcnt) {
 		root = BTRFS_I(bvec->bv_page->mapping->host)->root;
-		ret = csum_dirty_buffer(root, bvec->bv_page);
+		ret = csum_dirty_buffer(root, bvec->bv_page, bvec->bv_offset,
+					bvec->bv_len);
 		if (ret)
 			break;
 		bio_index++;
@@ -1007,9 +1076,13 @@  static int btree_set_page_dirty(struct page *page)
 	BUG_ON(!PagePrivate(page));
 	eb = (struct extent_buffer *)page->private;
 	BUG_ON(!eb);
-	BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
-	BUG_ON(!atomic_read(&eb->refs));
-	btrfs_assert_tree_locked(eb);
+	/* There doesn't seem to be a method for passing the correct eb
+	 * to this function, so no sanity checks for subpagesize blocksize. */
+	if (eb->len >= PAGE_SIZE) {
+		BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+		BUG_ON(!atomic_read(&eb->refs));
+		btrfs_assert_tree_locked(eb);
+	}
 #endif
 	return __set_page_dirty_nobuffers(page);
 }
@@ -2400,11 +2473,14 @@  int open_ctree(struct super_block *sb,
 		goto fail_sb_buffer;
 	}
 
+#if 0
+	// Hmm. How to deal wth this for subpagesize blocksize?
 	if (sectorsize != PAGE_SIZE) {
 		printk(KERN_WARNING "btrfs: Incompatible sector size(%lu) "
 		       "found on %s\n", (unsigned long)sectorsize, sb->s_id);
 		goto fail_sb_buffer;
 	}
+#endif
 
 	mutex_lock(&fs_info->chunk_mutex);
 	ret = btrfs_read_sys_array(tree_root);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1b319df..c1e052e 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2519,7 +2519,7 @@  static int submit_extent_page(int rw, struct extent_io_tree *tree,
 	int contig = 0;
 	int this_compressed = bio_flags & EXTENT_BIO_COMPRESSED;
 	int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
-	size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);
+	size_t bio_size = min_t(size_t, size, PAGE_CACHE_SIZE);
 
 	if (bio_ret && *bio_ret) {
 		bio = *bio_ret;
@@ -2530,8 +2530,8 @@  static int submit_extent_page(int rw, struct extent_io_tree *tree,
 				sector;
 
 		if (prev_bio_flags != bio_flags || !contig ||
-		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
-		    bio_add_page(bio, page, page_size, offset) < page_size) {
+		    merge_bio(tree, page, offset, bio_size, bio, bio_flags) ||
+		    bio_add_page(bio, page, bio_size, offset) < bio_size) {
 			ret = submit_one_bio(rw, bio, mirror_num,
 					     prev_bio_flags);
 			if (ret < 0)
@@ -2550,7 +2550,7 @@  static int submit_extent_page(int rw, struct extent_io_tree *tree,
 	if (!bio)
 		return -ENOMEM;
 
-	bio_add_page(bio, page, page_size, offset);
+	bio_add_page(bio, page, bio_size, offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;
 
@@ -3168,14 +3168,28 @@  static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
 	int uptodate = err == 0;
 	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
 	struct extent_buffer *eb;
+	unsigned int offset;
+	unsigned int bv_len;
+	u64 start;
 	int done;
 
 	do {
 		struct page *page = bvec->bv_page;
+		offset = bvec->bv_offset;
+		bv_len = bvec->bv_len;
+		start = ((u64)page->index << PAGE_CACHE_SHIFT) + offset;
 
 		bvec--;
 		eb = (struct extent_buffer *)page->private;
 		BUG_ON(!eb);
+		if (eb->len < PAGE_SIZE) {
+			while (eb->start != start) {
+				eb = eb->next;
+				BUG_ON(!eb);
+			}
+		}
+
+next_eb:
 		done = atomic_dec_and_test(&eb->io_pages);
 
 		if (!uptodate || test_bit(EXTENT_BUFFER_IOERR, &eb->bflags)) {
@@ -3184,12 +3198,50 @@  static void end_bio_extent_buffer_writepage(struct bio *bio, int err)
 			SetPageError(page);
 		}
 
-		end_page_writeback(page);
+		if (eb->len >= PAGE_SIZE) {
+			end_page_writeback(page);
 
-		if (!done)
-			continue;
+			if (!done)
+				continue;
 
-		end_extent_buffer_writeback(eb);
+			end_extent_buffer_writeback(eb);
+		} else {
+			/* Sanity checks. */
+			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+				WARN_ON(1);
+
+			/* Ensure I/O page count is zero. */
+			if (!done)
+				WARN_ON(1);
+
+			/* Clear the extent buffer's writeback flag. */
+			end_extent_buffer_writeback(eb);
+
+			/*
+			 * See if any other extent buffers exists within the
+			 * page.
+			 */
+			bv_len -= eb->len;
+			BUG_ON(bv_len & (eb->len - 1));
+			if (bv_len) {
+				eb = eb->next;
+				goto next_eb;
+			}
+
+			/* Clear the page writeback flag. */
+			eb = (struct extent_buffer *)page->private;
+			BUG_ON(!eb); /* Can this even happen? */
+			do {
+				if (!eb) {
+					end_page_writeback(page);
+					break;
+				}
+				if (test_bit(EXTENT_BUFFER_WRITEBACK,
+					     &eb->bflags))
+					break;
+				eb = eb->next;
+			} while (1);
+		}
 	} while (bvec >= bio->bi_io_vec);
 
 	bio_put(bio);
@@ -3202,7 +3254,8 @@  static int write_one_eb(struct extent_buffer *eb,
 			struct extent_page_data *epd)
 {
 	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
-	u64 offset = eb->start;
+	u64 start = eb->start;
+	unsigned long offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i, num_pages;
 	unsigned long bio_flags = 0;
 	int rw = (epd->sync_io ? WRITE_SYNC : WRITE);
@@ -3219,10 +3272,10 @@  static int write_one_eb(struct extent_buffer *eb,
 
 		clear_page_dirty_for_io(p);
 		set_page_writeback(p);
-		ret = submit_extent_page(rw, eb->tree, p, offset >> 9,
-					 PAGE_CACHE_SIZE, 0, bdev, &epd->bio,
-					 -1, end_bio_extent_buffer_writepage,
-					 0, epd->bio_flags, bio_flags);
+		ret = submit_extent_page(rw, eb->tree, p, start >> 9, eb->len,
+					offset, bdev, &epd->bio, -1,
+					end_bio_extent_buffer_writepage, 0,
+					epd->bio_flags, bio_flags);
 		epd->bio_flags = bio_flags;
 		if (ret) {
 			set_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
@@ -3232,7 +3285,7 @@  static int write_one_eb(struct extent_buffer *eb,
 			ret = -EIO;
 			break;
 		}
-		offset += PAGE_CACHE_SIZE;
+		start += PAGE_CACHE_SIZE;
 		update_nr_written(p, wbc, 1);
 		unlock_page(p);
 	}
@@ -3252,7 +3305,7 @@  int btree_write_cache_pages(struct address_space *mapping,
 {
 	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
 	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
-	struct extent_buffer *eb, *prev_eb = NULL;
+	struct extent_buffer *eb, *next, *prev_eb = NULL;
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
@@ -3326,17 +3379,41 @@  retry:
 				spin_unlock(&mapping->private_lock);
 				continue;
 			}
+			prev_eb = eb;
+
+next_eb:
+			next = eb->next;
 
 			ret = atomic_inc_not_zero(&eb->refs);
-			spin_unlock(&mapping->private_lock);
-			if (!ret)
-				continue;
+			if (eb->len >= PAGE_SIZE) {
+				spin_unlock(&mapping->private_lock);
+				if (!ret)
+					continue;
+			} else {
+				if (!ret)
+					goto inc_eb;
+				spin_unlock(&mapping->private_lock);
+
+				if (!test_bit(EXTENT_BUFFER_DIRTY,
+					      &eb->bflags)) {
+					spin_lock(&mapping->private_lock);
+					atomic_dec(&eb->refs);
+					ret = 0;
+					goto inc_eb;
+				}
+			}
 
-			prev_eb = eb;
 			ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
 			if (!ret) {
+				if (!(eb->len >= PAGE_SIZE))
+					spin_lock(&mapping->private_lock);
+
 				free_extent_buffer(eb);
-				continue;
+
+				if (eb->len >= PAGE_SIZE)
+					continue;
+				else
+					goto inc_eb;
 			}
 
 			ret = write_one_eb(eb, fs_info, wbc, &epd);
@@ -3345,8 +3422,26 @@  retry:
 				free_extent_buffer(eb);
 				break;
 			}
+
+			if (eb->len >= PAGE_SIZE) {
+				free_extent_buffer(eb);
+				goto written;
+			}
+
+			if (next)
+				spin_lock(&mapping->private_lock);
 			free_extent_buffer(eb);
 
+inc_eb:
+			if (!next) {
+				if (spin_is_locked(&mapping->private_lock))
+					spin_unlock(&mapping->private_lock);
+				goto written;
+			}
+			eb = next;
+			goto next_eb;
+
+written:
 			/*
 			 * the filesystem may choose to bump up nr_to_write.
 			 * We have to make sure to honor the new nr_to_write
@@ -4000,6 +4095,18 @@  static void __free_extent_buffer(struct extent_buffer *eb)
 	kmem_cache_free(extent_buffer_cache, eb);
 }
 
+/* Helper function to free extent buffers when there are multiple
+ * extent buffers per page. */
+static void __free_extent_buffers(struct extent_buffer *eb)
+{
+	struct extent_buffer *next;
+
+	do {
+		next = eb->next;
+		__free_extent_buffer(eb);
+	} while ((eb = next));
+}
+
 static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
 						   u64 start,
 						   unsigned long len,
@@ -4017,6 +4124,7 @@  static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
 	eb->len = len;
 	eb->tree = tree;
 	eb->bflags = 0;
+	eb->next = NULL;
 	rwlock_init(&eb->lock);
 	atomic_set(&eb->write_locks, 0);
 	atomic_set(&eb->read_locks, 0);
@@ -4054,6 +4162,62 @@  static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
 	return eb;
 }
 
+/* Allocates an array of extent buffers for the specified page.
+ * Should be called with the mapping's spin lock set. */
+static struct extent_buffer *__alloc_extent_buffers(struct extent_io_tree *tree,
+						    struct page *page,
+						    gfp_t mask)
+{
+	u32 blocksize_bits;
+	struct btrfs_inode *inode;
+	struct extent_buffer *eb_head;
+	struct extent_buffer *eb_cur;
+	u64 start;
+	unsigned long len;
+	int i;
+
+	/* Initialize variables. */
+	inode = BTRFS_I(tree->mapping->host);
+	blocksize_bits = inode->vfs_inode.i_sb->s_blocksize_bits;
+
+	/* Calculate extent buffer dimensions. */
+	start = page->index << PAGE_CACHE_SHIFT;
+	len = inode->root->leafsize;
+
+	/* Allocate the head extent buffer. */
+	eb_head = __alloc_extent_buffer(tree, start, len, GFP_NOFS);
+	if (!eb_head) {
+		WARN_ON(1);
+		return NULL;
+	}
+	start += len;
+	eb_head->pages[0] = page;
+	eb_cur = eb_head;
+
+	/* Allocate the other extent buffers. */
+	for (i = 1; i < (PAGE_CACHE_SIZE >> blocksize_bits); i++) {
+		eb_cur->next = __alloc_extent_buffer(tree, start, len,
+						     GFP_NOFS);
+		if (!eb_cur->next) {
+			WARN_ON(1);
+			goto free_ebs;
+		}
+		start += len;
+		eb_cur = eb_cur->next;
+		eb_cur->pages[0] = page;
+	}
+
+	/* Return the extent buffer head. */
+	return eb_head;
+
+free_ebs:
+	/* Free each extent buffer. */
+	// TODO: Implement.
+	pr_crit(KERN_CRIT "HACK: Need to implement this...\n");
+	WARN_ON(1);
+	return NULL;
+}
+
 struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
 {
 	unsigned long i;
@@ -4170,12 +4334,121 @@  static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
 }
 
 /*
+ * Frees the page if all extent buffers belonging to the page are not
+ * referernced. The extent buffers themselves must be free afterwards, too...
+ * ret:	0 if the page did not need to be freed; 1 if the page was freed.
+ */
+static int btrfs_release_extent_buffers_page(struct extent_buffer *eb,
+						struct extent_buffer **eb_head)
+{
+	struct extent_buffer *eb_cur;
+	struct extent_buffer *eb_temp;
+	struct page *page;
+	int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
+	int ret = 0;
+
+	if (extent_buffer_under_io(eb))
+		BUG_ON(1);
+
+	// ...is this even possible?
+	if (!num_extent_pages(eb->start, eb->len)) {
+		WARN_ON(1);
+		return ret;
+	}
+
+	page = extent_buffer_page(eb, 0);
+	if (page && mapped) {
+		spin_lock(&page->mapping->private_lock);
+		/*
+		 * We do this since we'll remove the pages after we've
+		 * removed the eb from the radix tree, so we could race
+		 * and have this page now attached to the new eb.  So
+		 * only clear page_private if it's still connected to
+		 * this eb.
+		 */
+		if (!PagePrivate(page)) {
+			spin_unlock(&page->mapping->private_lock);
+		} else {
+			/* Find the page eb corresponding to our eb. */
+			eb_cur = (struct extent_buffer *)page->private;
+			while (eb_cur->start != eb->start) {
+				eb_cur = eb_cur->next;
+				BUG_ON(!eb_cur);
+			}
+
+			/* See if a new eb has been attached to the page. */
+			if (eb_cur != eb) {
+				spin_unlock(&page->mapping->private_lock);
+				ret = 1;
+				goto page_release;
+			}
+
+			/* See if any other extent_buffer is using the page. */
+			eb_cur = (struct extent_buffer *)page->private;
+			do {
+				/* Check for any other references on the eb. */
+				spin_lock(&eb_cur->refs_lock);
+				if (!atomic_dec_and_test(&eb_cur->refs)) {
+					atomic_inc(&eb_cur->refs);
+					spin_unlock(&eb_cur->refs_lock);
+					eb_temp = eb_cur;
+					eb_cur = (struct extent_buffer *)
+						 page->private;
+					while (eb_cur != eb_temp) {
+						atomic_inc(&eb_cur->refs);
+						eb_cur = eb_cur->next;
+					}
+					spin_unlock(
+						&page->mapping->private_lock);
+					goto page_release;
+				}
+				spin_unlock(&eb_cur->refs_lock);
+			} while ((eb_cur = eb_cur->next) != NULL);
+
+			/* Sanity checks. */
+			eb_cur = (struct extent_buffer *)page->private;
+			do {
+				BUG_ON(extent_buffer_under_io(eb_cur));
+			} while ((eb_cur = eb_cur->next) != NULL);
+			BUG_ON(PageDirty(page));
+			BUG_ON(PageWriteback(page));
+			/*
+			 * We need to make sure we haven't been attached
+			 * to a new eb.
+			 */
+			eb_cur = (struct extent_buffer *)page->private;
+			*eb_head = eb_cur;
+			eb_temp = NULL;
+			ClearPagePrivate(page);
+			set_page_private(page, 0);
+			/* One for the page private. */
+			page_cache_release(page);
+			ret = 1;
+			spin_unlock(&page->mapping->private_lock);
+		}
+	}
+
+page_release:
+	if (page) {
+		/* One for when we alloced the page */
+		page_cache_release(page);
+	}
+	return ret;
+}
+
+/*
  * Helper for releasing the extent buffer.
  */
 static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
 {
-	btrfs_release_extent_buffer_page(eb, 0);
-	__free_extent_buffer(eb);
+	if (eb->len >= PAGE_SIZE) {
+		btrfs_release_extent_buffer_page(eb, 0);
+		__free_extent_buffer(eb);
+	} else {
+		struct extent_buffer *eb_head;
+		if (btrfs_release_extent_buffers_page(eb, &eb_head))
+			__free_extent_buffers(eb_head);
+	}
 }
 
 static void check_buffer_tree_ref(struct extent_buffer *eb)
@@ -4222,16 +4495,153 @@  static void mark_extent_buffer_accessed(struct extent_buffer *eb)
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 					  u64 start, unsigned long len)
 {
-	unsigned long num_pages = num_extent_pages(start, len);
-	unsigned long i;
-	unsigned long index = start >> PAGE_CACHE_SHIFT;
+	/* Allocate a new extent_buffer depending on blocksize*/
+	if (len < PAGE_CACHE_SIZE)
+		return alloc_extent_buffer_multiple(tree, start, len);
+	return alloc_extent_buffer_single(tree, start, len);
+}
+
+struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
+						   u64 start,
+						   unsigned long len) {
+
+	struct address_space *mapping;
+	u32 blocksize_bits;
+	struct btrfs_inode *btrfs_inode;
+	struct extent_buffer *eb_cur;
+	struct extent_buffer *eb_head;
+	struct extent_buffer *exists;
+	unsigned long index;
+	struct page *page;
+	int ret;
+
+	/* Initialize variables. */
+	btrfs_inode = BTRFS_I(tree->mapping->host);
+	blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
+
+	/* Sanity checks. */
+	WARN_ON(num_extent_pages(start, len) > 1);
+
+	/* See if the extent_buffer already exists in the radix tree. */
+	rcu_read_lock();
+	eb_cur = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
+	if (eb_cur && atomic_inc_not_zero(&eb_cur->refs)) {
+		rcu_read_unlock();
+		mark_extent_buffer_accessed(eb_cur);
+		return eb_cur;
+	}
+	rcu_read_unlock();
+
+	/* Find the page in the mapping. */
+	index = start >> PAGE_CACHE_SHIFT;
+	mapping = tree->mapping;
+	page = find_or_create_page(mapping, index, GFP_NOFS);
+	if (!page) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* Allocate each extent buffer for the page. */
+	eb_head = __alloc_extent_buffers(tree, page, GFP_NOFS);
+	if (!eb_head) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* See if extent buffers have already been allocated for
+	 * this page. */
+	spin_lock(&mapping->private_lock);
+	if (PagePrivate(page)) {
+		/*
+		 * We could have already allocated an eb for this page
+		 * and attached one so lets see if we can get a ref on
+		 * the existing eb, and if we can we know it's good and
+		 * we can just return that one, else we know we can just
+		 * overwrite page->private.
+		 */
+		eb_cur = (struct extent_buffer *)page->private;
+		while (eb_cur->start != start) {
+			eb_cur = eb_cur->next;
+			BUG_ON(!eb_cur);
+		}
+		check_buffer_tree_ref(eb_cur);
+		spin_unlock(&mapping->private_lock);
+		unlock_page(page);
+		mark_extent_buffer_accessed(eb_cur);
+		__free_extent_buffers(eb_head);
+		return eb_cur;
+	}
+
+	/* Bind the extent buffer to the page. */
+	attach_extent_buffer_page(eb_head, page);
+	spin_unlock(&mapping->private_lock);
+	WARN_ON(PageDirty(page));
+	mark_page_accessed(page);
+
+again:
+	/* Set eb_cur to the buffer added. */
+	eb_cur = eb_head;
+	while (start != eb_cur->start) {
+		eb_cur = eb_cur->next;
+		BUG_ON(!eb_cur);
+	}
+
+	/* Preload the radix tree. */
+	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+	if (ret) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* Add the extent buffer to the radix tree. */
+	spin_lock(&tree->buffer_lock);
+	ret = radix_tree_insert(&tree->buffer,
+				eb_cur->start >> blocksize_bits,
+				eb_cur);
+	if (ret == -EEXIST) {
+		exists = radix_tree_lookup(&tree->buffer,
+				eb_cur->start >> blocksize_bits);
+		if (exists->start != start)
+			BUG_ON(1);
+		if (!atomic_inc_not_zero(&exists->refs)) {
+			spin_unlock(&tree->buffer_lock);
+			radix_tree_preload_end();
+			exists = NULL;
+			goto again;
+		}
+		spin_unlock(&tree->buffer_lock);
+		radix_tree_preload_end();
+		mark_extent_buffer_accessed(exists);
+		WARN_ON(!atomic_dec_and_test(&eb_cur->refs));
+		btrfs_release_extent_buffer(eb_cur);
+		return exists;
+	}
+
+	/* Set the extent buffer's tree-reference bits. */
+	check_buffer_tree_ref(eb_cur);
+	spin_unlock(&tree->buffer_lock);
+	radix_tree_preload_end();
+
+	/* Not quite sure what this does. */
+	SetPageChecked(eb_head->pages[0]);
+	unlock_page(eb_head->pages[0]);
+
+	return eb_cur;
+}
+
+struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
+						 u64 start, unsigned long len) {
+	struct address_space *mapping = tree->mapping;
 	struct extent_buffer *eb;
 	struct extent_buffer *exists = NULL;
+	unsigned long i;
+	unsigned long index = start >> PAGE_CACHE_SHIFT;
+	unsigned long num_pages = num_extent_pages(start, len);
 	struct page *p;
-	struct address_space *mapping = tree->mapping;
 	int uptodate = 1;
 	int ret;
 
+	/* See if the extent_buffer already exists */
 	rcu_read_lock();
 	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
@@ -4350,9 +4760,17 @@  struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
 					 u64 start, unsigned long len)
 {
 	struct extent_buffer *eb;
+	struct btrfs_inode *btrfs_inode = BTRFS_I(tree->mapping->host);
+	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
 
 	rcu_read_lock();
-	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+	// This branch needs to be fixed when the allocation code is merged.
+	// Seriously.
+	if (blocksize_bits >= PAGE_CACHE_SHIFT)
+		eb = radix_tree_lookup(&tree->buffer,
+				       start >> PAGE_CACHE_SHIFT);
+	else
+		eb = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
 		rcu_read_unlock();
 		mark_extent_buffer_accessed(eb);
@@ -4371,9 +4789,25 @@  static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
 	__free_extent_buffer(eb);
 }
 
-/* Expects to have eb->eb_lock already held */
+/*
+ * The RCU head must point to the first extent buffer belonging to a page.
+ */
+static inline void btrfs_release_extent_buffers_rcu(struct rcu_head *head)
+{
+	struct extent_buffer *eb =
+			container_of(head, struct extent_buffer, rcu_head);
+
+	do {
+		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
+	} while ((eb = eb->next));
+}
+
+/* Expects to have eb->refs_lock already held */
 static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
 {
+	struct btrfs_inode *btrfs_inode = BTRFS_I(eb->tree->mapping->host);
+	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
+
 	WARN_ON(atomic_read(&eb->refs) == 0);
 	if (atomic_dec_and_test(&eb->refs)) {
 		if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
@@ -4381,17 +4815,35 @@  static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
 		} else {
 			struct extent_io_tree *tree = eb->tree;
 
+			/* Dumb hack to make releasing the page easier. */
+			if (eb->len < PAGE_SIZE)
+				atomic_inc(&eb->refs);
+
 			spin_unlock(&eb->refs_lock);
 
+			// This also needs to be fixed when allocation code is
+			// merged.
 			spin_lock(&tree->buffer_lock);
-			radix_tree_delete(&tree->buffer,
-					  eb->start >> PAGE_CACHE_SHIFT);
+			if (eb->len >= PAGE_SIZE)
+				radix_tree_delete(&tree->buffer,
+					  eb->start >> blocksize_bits);
+			else
+				radix_tree_delete(&tree->buffer,
+					  eb->start >> blocksize_bits);
 			spin_unlock(&tree->buffer_lock);
 		}
 
 		/* Should be safe to release our pages at this point */
-		btrfs_release_extent_buffer_page(eb, 0);
-		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
+		if (eb->len >= PAGE_SIZE) {
+			btrfs_release_extent_buffer_page(eb, 0);
+			call_rcu(&eb->rcu_head,
+				 btrfs_release_extent_buffer_rcu);
+		} else {
+			struct extent_buffer *eb_head;
+			if (btrfs_release_extent_buffers_page(eb, &eb_head))
+				btrfs_release_extent_buffers_rcu(
+							&eb_head->rcu_head);
+		}
 		return 1;
 	}
 	spin_unlock(&eb->refs_lock);
@@ -4482,6 +4934,11 @@  int set_extent_buffer_dirty(struct extent_buffer *eb)
 
 	for (i = 0; i < num_pages; i++)
 		set_page_dirty(extent_buffer_page(eb, i));
+	/* Run an additional sanity check here instead of
+	 * in btree_set_page_dirty() since we can't get the eb there for
+	 * subpage blocksize. */
+	if (eb->len < PAGE_SIZE)
+		btrfs_assert_tree_locked(eb);
 	return was_dirty;
 }
 
@@ -4503,11 +4960,14 @@  int clear_extent_buffer_uptodate(struct extent_buffer *eb)
 	unsigned long num_pages;
 
 	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-	num_pages = num_extent_pages(eb->start, eb->len);
-	for (i = 0; i < num_pages; i++) {
-		page = extent_buffer_page(eb, i);
-		if (page)
-			ClearPageUptodate(page);
+	/* Ignore the page's uptodate flag forsubpage blocksize. */
+	if (eb->len >= PAGE_SIZE) {
+		num_pages = num_extent_pages(eb->start, eb->len);
+		for (i = 0; i < num_pages; i++) {
+			page = extent_buffer_page(eb, i);
+			if (page)
+				ClearPageUptodate(page);
+		}
 	}
 	return 0;
 }
@@ -4518,11 +4978,16 @@  int set_extent_buffer_uptodate(struct extent_buffer *eb)
 	struct page *page;
 	unsigned long num_pages;
 
+	/* Set extent buffer up-to-date. */
 	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-	num_pages = num_extent_pages(eb->start, eb->len);
-	for (i = 0; i < num_pages; i++) {
-		page = extent_buffer_page(eb, i);
-		SetPageUptodate(page);
+
+	/* Set pages up-to-date. */
+	if (eb->len >= PAGE_CACHE_SIZE) {
+		num_pages = num_extent_pages(eb->start, eb->len);
+		for (i = 0; i < num_pages; i++) {
+			page = extent_buffer_page(eb, i);
+			SetPageUptodate(page);
+		}
 	}
 	return 0;
 }
@@ -4606,7 +5071,7 @@  int read_extent_buffer_pages(struct extent_io_tree *tree,
 		}
 	}
 	if (all_uptodate) {
-		if (start_i == 0)
+		if (start_i == 0 && eb->len >= PAGE_SIZE)
 			set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 		goto unlock_exit;
 	}
@@ -4693,7 +5158,7 @@  int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 			       unsigned long *map_start,
 			       unsigned long *map_len)
 {
-	size_t offset = start & (PAGE_CACHE_SIZE - 1);
+	size_t offset;
 	char *kaddr;
 	struct page *p;
 	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
@@ -4709,6 +5174,9 @@  int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 		*map_start = 0;
 	} else {
 		offset = 0;
+		// I'm pretty sure that this is a) just plain wrong and
+		// b) will never realistically execute; not entirely sure,
+		// though...
 		*map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
 	}
 
@@ -4722,7 +5190,7 @@  int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	p = extent_buffer_page(eb, i);
 	kaddr = page_address(p);
 	*map = kaddr + offset;
-	*map_len = PAGE_CACHE_SIZE - offset;
+	*map_len = (PAGE_CACHE_SIZE - offset) & (eb->len - 1);
 	return 0;
 }
 
@@ -4996,6 +5464,7 @@  void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
 int try_release_extent_buffer(struct page *page, gfp_t mask)
 {
 	struct extent_buffer *eb;
+	int ret;
 
 	/*
 	 * We need to make sure noboody is attaching this page to an eb right
@@ -5010,30 +5479,61 @@  int try_release_extent_buffer(struct page *page, gfp_t mask)
 	eb = (struct extent_buffer *)page->private;
 	BUG_ON(!eb);
 
-	/*
-	 * This is a little awful but should be ok, we need to make sure that
-	 * the eb doesn't disappear out from under us while we're looking at
-	 * this page.
-	 */
-	spin_lock(&eb->refs_lock);
-	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
-		spin_unlock(&eb->refs_lock);
+	if (eb->len >= PAGE_SIZE) {
+		/*
+		 * This is a little awful but should be ok, we need to make
+		 * sure that the eb doesn't disappear out from under us while
+		 * we're looking at this page.
+		 */
+		spin_lock(&eb->refs_lock);
+		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
+			spin_unlock(&eb->refs_lock);
+			spin_unlock(&page->mapping->private_lock);
+			return 0;
+		}
 		spin_unlock(&page->mapping->private_lock);
-		return 0;
-	}
-	spin_unlock(&page->mapping->private_lock);
 
-	if ((mask & GFP_NOFS) == GFP_NOFS)
-		mask = GFP_NOFS;
+		if ((mask & GFP_NOFS) == GFP_NOFS)
+			mask = GFP_NOFS;
 
-	/*
-	 * If tree ref isn't set then we know the ref on this eb is a real ref,
-	 * so just return, this page will likely be freed soon anyway.
-	 */
-	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
-		spin_unlock(&eb->refs_lock);
-		return 0;
-	}
+		/*
+		 * If tree ref isn't set then we know the ref on this eb is a
+		 * real ref, so just return, this page will likely be freed
+		 * soon anyway.
+		 */
+		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
+			spin_unlock(&eb->refs_lock);
+			return 0;
+		}
 
-	return release_extent_buffer(eb, mask);
+		return release_extent_buffer(eb, mask);
+	} else {
+		ret = 0;
+		do {
+			spin_lock(&eb->refs_lock);
+			if (atomic_read(&eb->refs) != 1 ||
+					extent_buffer_under_io(eb)) {
+				spin_unlock(&eb->refs_lock);
+				continue;
+			}
+			spin_unlock(&page->mapping->private_lock);
+
+			if ((mask & GFP_NOFS) == GFP_NOFS)
+				mask = GFP_NOFS;
+
+			if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF,
+						&eb->bflags)) {
+				spin_unlock(&eb->refs_lock);
+				spin_lock(&page->mapping->private_lock);
+				continue;
+			}
+
+			/* No idea what to do with the 'ret' here. */
+			ret |= release_extent_buffer(eb, mask);
+
+			spin_lock(&page->mapping->private_lock);
+		} while ((eb = eb->next) != NULL);
+		spin_unlock(&page->mapping->private_lock);
+		return ret;
+	}
 }
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 2eacfab..955ef5e 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -163,6 +163,9 @@  struct extent_buffer {
 	wait_queue_head_t lock_wq;
 	struct page *inline_pages[INLINE_EXTENT_BUFFER_PAGES];
 	struct page **pages;
+
+	/* Acyclic linked list of extent_buffers belonging to a single page. */
+	struct extent_buffer *next;
 };
 
 static inline void extent_set_compress_type(unsigned long *bio_flags,
@@ -270,6 +273,10 @@  void set_page_extent_mapped(struct page *page);
 
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 					  u64 start, unsigned long len);
+struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree *tree,
+						 u64 start, unsigned long len);
+struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree *tree,
+						 u64 start, unsigned long len);
 struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len);
 struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
 struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3bff4d4..8745289 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1340,7 +1340,7 @@  static noinline ssize_t __btrfs_buffered_write(struct file *file,
 		}
 
 		ret = btrfs_delalloc_reserve_space(inode,
-					num_pages << PAGE_CACHE_SHIFT);
+					write_bytes);
 		if (ret)
 			break;
 
@@ -1354,7 +1354,7 @@  static noinline ssize_t __btrfs_buffered_write(struct file *file,
 				    force_page_uptodate);
 		if (ret) {
 			btrfs_delalloc_release_space(inode,
-					num_pages << PAGE_CACHE_SHIFT);
+					write_bytes);
 			break;
 		}
 
@@ -1392,8 +1392,7 @@  static noinline ssize_t __btrfs_buffered_write(struct file *file,
 				spin_unlock(&BTRFS_I(inode)->lock);
 			}
 			btrfs_delalloc_release_space(inode,
-					(num_pages - dirty_pages) <<
-					PAGE_CACHE_SHIFT);
+						write_bytes - copied);
 		}
 
 		if (copied > 0) {
@@ -1402,7 +1401,7 @@  static noinline ssize_t __btrfs_buffered_write(struct file *file,
 						NULL);
 			if (ret) {
 				btrfs_delalloc_release_space(inode,
-					dirty_pages << PAGE_CACHE_SHIFT);
+						copied);
 				btrfs_drop_pages(pages, num_pages);
 				break;
 			}
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 59ea2e4..1c0e254 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -960,6 +960,8 @@  int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
 
 	if (block_group)
 		start = block_group->key.objectid;
+	else // Hmm I don't recall putting this here.
+		start = (u64)-1;
 
 	while (block_group && (start < block_group->key.objectid +
 			       block_group->key.offset)) {
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3368c10..11ff3dd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2040,22 +2040,38 @@  static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_ordered_extent *ordered_extent = NULL;
 	struct btrfs_workers *workers;
+	u64 block_size = 1 << inode->i_blkbits;
+	u64 io_size;
+
+	if (block_size >= PAGE_CACHE_SIZE)
+		io_size = end - start + 1;
+	else
+		io_size = block_size;
 
 	trace_btrfs_writepage_end_io_hook(page, start, end, uptodate);
 
 	ClearPagePrivate2(page);
-	if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
-					    end - start + 1, uptodate))
-		return 0;
-
-	ordered_extent->work.func = finish_ordered_fn;
-	ordered_extent->work.flags = 0;
-
-	if (btrfs_is_free_space_inode(inode))
-		workers = &root->fs_info->endio_freespace_worker;
-	else
-		workers = &root->fs_info->endio_write_workers;
-	btrfs_queue_worker(workers, &ordered_extent->work);
+next_block:
+	if (btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
+					    io_size, uptodate)) {
+		ordered_extent->work.func = finish_ordered_fn;
+		ordered_extent->work.flags = 0;
+
+		if (btrfs_is_free_space_inode(inode))
+			workers = &root->fs_info->endio_freespace_worker;
+		else
+			workers = &root->fs_info->endio_write_workers;
+		btrfs_queue_worker(workers, &ordered_extent->work);
+	}
+
+	// I think that writes are always block-size granularity.
+	if (block_size < PAGE_CACHE_SIZE)
+		BUG_ON(start & (io_size - 1)); // Welp, one way to make sure...
+	start += io_size;
+	if (start < end)
+		goto next_block;
+	// We overshot. I'm pretty sure that this is terrible.
+	BUG_ON(start != (end + 1));
 
 	return 0;
 }
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 657d83c..c0269df 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3937,8 +3937,8 @@  long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(file, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(file, argp);
-	case BTRFS_IOC_DEV_REPLACE:
-		return btrfs_ioctl_dev_replace(root, argp);
+	//case BTRFS_IOC_DEV_REPLACE:
+//		return btrfs_ioctl_dev_replace(root, argp);
 	}
 
 	return -ENOTTY;