| Message ID | 20210106010201.37864-9-wqu@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: add read-only support for subpage sector size | expand |
On 2021/1/6 上午9:01, Qu Wenruo wrote: > For subpage case, we need to allocate new memory for each metadata page. > > So we need to: > - Allow attach_extent_buffer_page() to return int > To indicate allocation failure > > - Prealloc page->private for alloc_extent_buffer() > We don't want to call memory allocation with spinlock hold, so > do preallocation before we acquire the spin lock. > > - Handle subpage and regular case differently in > attach_extent_buffer_page() > For regular case, just do the usual thing. > For subpage case, allocate new memory and update the tree_block > bitmap. > > The bitmap update will be handled by new subpage specific helper, > btrfs_subpage_set_tree_block(). > > Signed-off-by: Qu Wenruo <wqu@suse.com> > --- > fs/btrfs/extent_io.c | 74 ++++++++++++++++++++++++++++++++++---------- > fs/btrfs/subpage.h | 50 ++++++++++++++++++++++++++++++ > 2 files changed, 108 insertions(+), 16 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index d60f1837f8fb..2eeff925450f 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -24,6 +24,7 @@ > #include "rcu-string.h" > #include "backref.h" > #include "disk-io.h" > +#include "subpage.h" > > static struct kmem_cache *extent_state_cache; > static struct kmem_cache *extent_buffer_cache; > @@ -3140,22 +3141,41 @@ static int submit_extent_page(unsigned int opf, > return ret; > } > > -static void attach_extent_buffer_page(struct extent_buffer *eb, > +static int attach_extent_buffer_page(struct extent_buffer *eb, > struct page *page) > { > - /* > - * If the page is mapped to btree inode, we should hold the private > - * lock to prevent race. > - * For cloned or dummy extent buffers, their pages are not mapped and > - * will not race with any other ebs. > - */ > - if (page->mapping) > - lockdep_assert_held(&page->mapping->private_lock); > + struct btrfs_fs_info *fs_info = eb->fs_info; > + int ret; > > - if (!PagePrivate(page)) > - attach_page_private(page, eb); > - else > - WARN_ON(page->private != (unsigned long)eb); > + if (fs_info->sectorsize == PAGE_SIZE) { > + /* > + * If the page is mapped to btree inode, we should hold the > + * private lock to prevent race. > + * For cloned or dummy extent buffers, their pages are not > + * mapped and will not race with any other ebs. > + */ > + if (page->mapping) > + lockdep_assert_held(&page->mapping->private_lock); > + > + if (!PagePrivate(page)) > + attach_page_private(page, eb); > + else > + WARN_ON(page->private != (unsigned long)eb); > + return 0; > + } > + > + /* Already mapped, just update the existing range */ > + if (PagePrivate(page)) > + goto update_bitmap; > + > + /* Do new allocation to attach subpage */ > + ret = btrfs_attach_subpage(fs_info, page); > + if (ret < 0) > + return ret; > + > +update_bitmap: > + btrfs_subpage_set_tree_block(fs_info, page, eb->start, eb->len); > + return 0; > } > > void set_page_extent_mapped(struct page *page) > @@ -5063,21 +5083,29 @@ struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src) > if (new == NULL) > return NULL; > > + set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); > + set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); > + > for (i = 0; i < num_pages; i++) { > + int ret; > + > p = alloc_page(GFP_NOFS); > if (!p) { > btrfs_release_extent_buffer(new); > return NULL; > } > - attach_extent_buffer_page(new, p); > + ret = attach_extent_buffer_page(new, p); > + if (ret < 0) { > + put_page(p); > + btrfs_release_extent_buffer(new); > + return NULL; > + } > WARN_ON(PageDirty(p)); > SetPageUptodate(p); > new->pages[i] = p; > copy_page(page_address(p), page_address(src->pages[i])); > } > > - set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); > - set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); > > return new; > } > @@ -5316,6 +5344,18 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, > goto free_eb; > } > > + /* > + * Preallocate page->private for subpage case, so that > + * we won't allocate memory with private_lock hold. > + */ > + ret = btrfs_attach_subpage(fs_info, p); Although we try to preallocate the subpage structure here, it's not reliable. I have hit a case just minutes before, where we still try to allocate memory inside that private_lock spinlock, and causes sleep inside atomic warning. The problem is, we can have a race where the page has one existing eb, and it's being freed. At this point, we still have page::private. But before we acquire that private_lock, the eb get freed and since it's the only eb of that page (our eb hasn't yet being added to the page), it detach page private. > + if (ret < 0) { > + unlock_page(p); > + put_page(p); > + exists = ERR_PTR(-ENOMEM); > + goto free_eb; > + } > + > spin_lock(&mapping->private_lock); > exists = grab_extent_buffer(p); > if (exists) { > @@ -5325,8 +5365,10 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, > mark_extent_buffer_accessed(exists, p); > goto free_eb; > } > + /* Should not fail, as we have attached the subpage already */ > attach_extent_buffer_page(eb, p); So here we can not rely on any result before we acquire private_lock. Thus I guess we have to pre-allocate the memory manually and pass the pointer in. Why I didn't hit the bug before sending the patches... Thanks, Qu > spin_unlock(&mapping->private_lock); > + > WARN_ON(PageDirty(p)); > eb->pages[i] = p; > if (!PageUptodate(p)) > diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h > index 96f3b226913e..e49d4a7329e1 100644 > --- a/fs/btrfs/subpage.h > +++ b/fs/btrfs/subpage.h > @@ -23,9 +23,59 @@ > struct btrfs_subpage { > /* Common members for both data and metadata pages */ > spinlock_t lock; > + union { > + /* Structures only used by metadata */ > + struct { > + u16 tree_block_bitmap; > + }; > + /* structures only used by data */ > + }; > }; > > int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page); > void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page); > > +/* > + * Convert the [start, start + len) range into a u16 bitmap > + * > + * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0. > + */ > +static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info *fs_info, > + struct page *page, u64 start, u32 len) > +{ > + int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits; > + int nbits = len >> fs_info->sectorsize_bits; > + > + /* Basic checks */ > + ASSERT(PagePrivate(page) && page->private); > + ASSERT(IS_ALIGNED(start, fs_info->sectorsize) && > + IS_ALIGNED(len, fs_info->sectorsize)); > + > + /* > + * The range check only works for mapped page, we can > + * still have unampped page like dummy extent buffer pages. > + */ > + if (page->mapping) > + ASSERT(page_offset(page) <= start && > + start + len <= page_offset(page) + PAGE_SIZE); > + /* > + * Here nbits can be 16, thus can go beyond u16 range. Here we make the > + * first left shift to be calculated in unsigned long (u32), then > + * truncate the result to u16. > + */ > + return (u16)(((1UL << nbits) - 1) << bit_start); > +} > + > +static inline void btrfs_subpage_set_tree_block(struct btrfs_fs_info *fs_info, > + struct page *page, u64 start, u32 len) > +{ > + struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; > + unsigned long flags; > + u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); > + > + spin_lock_irqsave(&subpage->lock, flags); > + subpage->tree_block_bitmap |= tmp; > + spin_unlock_irqrestore(&subpage->lock, flags); > +} > + > #endif /* BTRFS_SUBPAGE_H */ >
On 2021/1/6 上午9:01, Qu Wenruo wrote: > For subpage case, we need to allocate new memory for each metadata page. > > So we need to: > - Allow attach_extent_buffer_page() to return int > To indicate allocation failure > > - Prealloc page->private for alloc_extent_buffer() > We don't want to call memory allocation with spinlock hold, so > do preallocation before we acquire the spin lock. > > - Handle subpage and regular case differently in > attach_extent_buffer_page() > For regular case, just do the usual thing. > For subpage case, allocate new memory and update the tree_block > bitmap. > > The bitmap update will be handled by new subpage specific helper, > btrfs_subpage_set_tree_block(). > > Signed-off-by: Qu Wenruo <wqu@suse.com> > --- > fs/btrfs/extent_io.c | 74 ++++++++++++++++++++++++++++++++++---------- > fs/btrfs/subpage.h | 50 ++++++++++++++++++++++++++++++ > 2 files changed, 108 insertions(+), 16 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index d60f1837f8fb..2eeff925450f 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -24,6 +24,7 @@ > #include "rcu-string.h" > #include "backref.h" > #include "disk-io.h" > +#include "subpage.h" > > static struct kmem_cache *extent_state_cache; > static struct kmem_cache *extent_buffer_cache; > @@ -3140,22 +3141,41 @@ static int submit_extent_page(unsigned int opf, > return ret; > } > > -static void attach_extent_buffer_page(struct extent_buffer *eb, > +static int attach_extent_buffer_page(struct extent_buffer *eb, > struct page *page) > { > - /* > - * If the page is mapped to btree inode, we should hold the private > - * lock to prevent race. > - * For cloned or dummy extent buffers, their pages are not mapped and > - * will not race with any other ebs. > - */ > - if (page->mapping) > - lockdep_assert_held(&page->mapping->private_lock); > + struct btrfs_fs_info *fs_info = eb->fs_info; > + int ret; > > - if (!PagePrivate(page)) > - attach_page_private(page, eb); > - else > - WARN_ON(page->private != (unsigned long)eb); > + if (fs_info->sectorsize == PAGE_SIZE) { > + /* > + * If the page is mapped to btree inode, we should hold the > + * private lock to prevent race. > + * For cloned or dummy extent buffers, their pages are not > + * mapped and will not race with any other ebs. > + */ > + if (page->mapping) > + lockdep_assert_held(&page->mapping->private_lock); > + > + if (!PagePrivate(page)) > + attach_page_private(page, eb); > + else > + WARN_ON(page->private != (unsigned long)eb); > + return 0; > + } > + > + /* Already mapped, just update the existing range */ > + if (PagePrivate(page)) > + goto update_bitmap; > + > + /* Do new allocation to attach subpage */ > + ret = btrfs_attach_subpage(fs_info, page); > + if (ret < 0) > + return ret; > + > +update_bitmap: > + btrfs_subpage_set_tree_block(fs_info, page, eb->start, eb->len); > + return 0; > } > > void set_page_extent_mapped(struct page *page) > @@ -5063,21 +5083,29 @@ struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src) > if (new == NULL) > return NULL; > > + set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); > + set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); > + > for (i = 0; i < num_pages; i++) { > + int ret; > + > p = alloc_page(GFP_NOFS); > if (!p) { > btrfs_release_extent_buffer(new); > return NULL; > } > - attach_extent_buffer_page(new, p); > + ret = attach_extent_buffer_page(new, p); > + if (ret < 0) { > + put_page(p); > + btrfs_release_extent_buffer(new); > + return NULL; > + } > WARN_ON(PageDirty(p)); > SetPageUptodate(p); > new->pages[i] = p; > copy_page(page_address(p), page_address(src->pages[i])); > } > > - set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); > - set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); > > return new; > } > @@ -5316,6 +5344,18 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, > goto free_eb; > } > > + /* > + * Preallocate page->private for subpage case, so that > + * we won't allocate memory with private_lock hold. > + */ > + ret = btrfs_attach_subpage(fs_info, p); > + if (ret < 0) { > + unlock_page(p); > + put_page(p); > + exists = ERR_PTR(-ENOMEM); > + goto free_eb; > + } > + > spin_lock(&mapping->private_lock); > exists = grab_extent_buffer(p); > if (exists) { > @@ -5325,8 +5365,10 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, > mark_extent_buffer_accessed(exists, p); > goto free_eb; > } > + /* Should not fail, as we have attached the subpage already */ > attach_extent_buffer_page(eb, p); > spin_unlock(&mapping->private_lock); > + > WARN_ON(PageDirty(p)); > eb->pages[i] = p; > if (!PageUptodate(p)) > diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h > index 96f3b226913e..e49d4a7329e1 100644 > --- a/fs/btrfs/subpage.h > +++ b/fs/btrfs/subpage.h > @@ -23,9 +23,59 @@ > struct btrfs_subpage { > /* Common members for both data and metadata pages */ > spinlock_t lock; > + union { > + /* Structures only used by metadata */ > + struct { > + u16 tree_block_bitmap; > + }; After more investigation, the idea of using subpage structure to record tree blocks bitmap may not be a good idea. The main problem is the synchronization for the bit and extent buffer, which have different lock schemas. I'll try to use radix tree only to do the check, other than relying on some extra bit. Thanks, Qu > + /* structures only used by data */ > + }; > }; > > int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page); > void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page); > > +/* > + * Convert the [start, start + len) range into a u16 bitmap > + * > + * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0. > + */ > +static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info *fs_info, > + struct page *page, u64 start, u32 len) > +{ > + int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits; > + int nbits = len >> fs_info->sectorsize_bits; > + > + /* Basic checks */ > + ASSERT(PagePrivate(page) && page->private); > + ASSERT(IS_ALIGNED(start, fs_info->sectorsize) && > + IS_ALIGNED(len, fs_info->sectorsize)); > + > + /* > + * The range check only works for mapped page, we can > + * still have unampped page like dummy extent buffer pages. > + */ > + if (page->mapping) > + ASSERT(page_offset(page) <= start && > + start + len <= page_offset(page) + PAGE_SIZE); > + /* > + * Here nbits can be 16, thus can go beyond u16 range. Here we make the > + * first left shift to be calculated in unsigned long (u32), then > + * truncate the result to u16. > + */ > + return (u16)(((1UL << nbits) - 1) << bit_start); > +} > + > +static inline void btrfs_subpage_set_tree_block(struct btrfs_fs_info *fs_info, > + struct page *page, u64 start, u32 len) > +{ > + struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; > + unsigned long flags; > + u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); > + > + spin_lock_irqsave(&subpage->lock, flags); > + subpage->tree_block_bitmap |= tmp; > + spin_unlock_irqrestore(&subpage->lock, flags); > +} > + > #endif /* BTRFS_SUBPAGE_H */ >
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index d60f1837f8fb..2eeff925450f 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -24,6 +24,7 @@ #include "rcu-string.h" #include "backref.h" #include "disk-io.h" +#include "subpage.h" static struct kmem_cache *extent_state_cache; static struct kmem_cache *extent_buffer_cache; @@ -3140,22 +3141,41 @@ static int submit_extent_page(unsigned int opf, return ret; } -static void attach_extent_buffer_page(struct extent_buffer *eb, +static int attach_extent_buffer_page(struct extent_buffer *eb, struct page *page) { - /* - * If the page is mapped to btree inode, we should hold the private - * lock to prevent race. - * For cloned or dummy extent buffers, their pages are not mapped and - * will not race with any other ebs. - */ - if (page->mapping) - lockdep_assert_held(&page->mapping->private_lock); + struct btrfs_fs_info *fs_info = eb->fs_info; + int ret; - if (!PagePrivate(page)) - attach_page_private(page, eb); - else - WARN_ON(page->private != (unsigned long)eb); + if (fs_info->sectorsize == PAGE_SIZE) { + /* + * If the page is mapped to btree inode, we should hold the + * private lock to prevent race. + * For cloned or dummy extent buffers, their pages are not + * mapped and will not race with any other ebs. + */ + if (page->mapping) + lockdep_assert_held(&page->mapping->private_lock); + + if (!PagePrivate(page)) + attach_page_private(page, eb); + else + WARN_ON(page->private != (unsigned long)eb); + return 0; + } + + /* Already mapped, just update the existing range */ + if (PagePrivate(page)) + goto update_bitmap; + + /* Do new allocation to attach subpage */ + ret = btrfs_attach_subpage(fs_info, page); + if (ret < 0) + return ret; + +update_bitmap: + btrfs_subpage_set_tree_block(fs_info, page, eb->start, eb->len); + return 0; } void set_page_extent_mapped(struct page *page) @@ -5063,21 +5083,29 @@ struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src) if (new == NULL) return NULL; + set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); + set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); + for (i = 0; i < num_pages; i++) { + int ret; + p = alloc_page(GFP_NOFS); if (!p) { btrfs_release_extent_buffer(new); return NULL; } - attach_extent_buffer_page(new, p); + ret = attach_extent_buffer_page(new, p); + if (ret < 0) { + put_page(p); + btrfs_release_extent_buffer(new); + return NULL; + } WARN_ON(PageDirty(p)); SetPageUptodate(p); new->pages[i] = p; copy_page(page_address(p), page_address(src->pages[i])); } - set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags); - set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); return new; } @@ -5316,6 +5344,18 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, goto free_eb; } + /* + * Preallocate page->private for subpage case, so that + * we won't allocate memory with private_lock hold. + */ + ret = btrfs_attach_subpage(fs_info, p); + if (ret < 0) { + unlock_page(p); + put_page(p); + exists = ERR_PTR(-ENOMEM); + goto free_eb; + } + spin_lock(&mapping->private_lock); exists = grab_extent_buffer(p); if (exists) { @@ -5325,8 +5365,10 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, mark_extent_buffer_accessed(exists, p); goto free_eb; } + /* Should not fail, as we have attached the subpage already */ attach_extent_buffer_page(eb, p); spin_unlock(&mapping->private_lock); + WARN_ON(PageDirty(p)); eb->pages[i] = p; if (!PageUptodate(p)) diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h index 96f3b226913e..e49d4a7329e1 100644 --- a/fs/btrfs/subpage.h +++ b/fs/btrfs/subpage.h @@ -23,9 +23,59 @@ struct btrfs_subpage { /* Common members for both data and metadata pages */ spinlock_t lock; + union { + /* Structures only used by metadata */ + struct { + u16 tree_block_bitmap; + }; + /* structures only used by data */ + }; }; int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page); void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page); +/* + * Convert the [start, start + len) range into a u16 bitmap + * + * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0. + */ +static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info *fs_info, + struct page *page, u64 start, u32 len) +{ + int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits; + int nbits = len >> fs_info->sectorsize_bits; + + /* Basic checks */ + ASSERT(PagePrivate(page) && page->private); + ASSERT(IS_ALIGNED(start, fs_info->sectorsize) && + IS_ALIGNED(len, fs_info->sectorsize)); + + /* + * The range check only works for mapped page, we can + * still have unampped page like dummy extent buffer pages. + */ + if (page->mapping) + ASSERT(page_offset(page) <= start && + start + len <= page_offset(page) + PAGE_SIZE); + /* + * Here nbits can be 16, thus can go beyond u16 range. Here we make the + * first left shift to be calculated in unsigned long (u32), then + * truncate the result to u16. + */ + return (u16)(((1UL << nbits) - 1) << bit_start); +} + +static inline void btrfs_subpage_set_tree_block(struct btrfs_fs_info *fs_info, + struct page *page, u64 start, u32 len) +{ + struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; + unsigned long flags; + u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); + + spin_lock_irqsave(&subpage->lock, flags); + subpage->tree_block_bitmap |= tmp; + spin_unlock_irqrestore(&subpage->lock, flags); +} + #endif /* BTRFS_SUBPAGE_H */
For subpage case, we need to allocate new memory for each metadata page. So we need to: - Allow attach_extent_buffer_page() to return int To indicate allocation failure - Prealloc page->private for alloc_extent_buffer() We don't want to call memory allocation with spinlock hold, so do preallocation before we acquire the spin lock. - Handle subpage and regular case differently in attach_extent_buffer_page() For regular case, just do the usual thing. For subpage case, allocate new memory and update the tree_block bitmap. The bitmap update will be handled by new subpage specific helper, btrfs_subpage_set_tree_block(). Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/extent_io.c | 74 ++++++++++++++++++++++++++++++++++---------- fs/btrfs/subpage.h | 50 ++++++++++++++++++++++++++++++ 2 files changed, 108 insertions(+), 16 deletions(-)