| Message ID | 20190909182722.16783-7-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/19] iomap: better document the IOMAP_F_* flags | expand |
On Mon, Sep 09, 2019 at 08:27:09PM +0200, Christoph Hellwig wrote: > Use the existing iomap write_begin code to read the pages unshared > by iomap_file_unshare. That avoids the extra ->readpage call and > extent tree lookup currently done by read_mapping_page. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > fs/iomap/buffered-io.c | 49 ++++++++++++++---------------------------- > 1 file changed, 16 insertions(+), 33 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index fe099faf540f..a421977a9496 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -533,6 +533,10 @@ iomap_migrate_page(struct address_space *mapping, struct page *newpage, > EXPORT_SYMBOL_GPL(iomap_migrate_page); > #endif /* CONFIG_MIGRATION */ > > +enum { > + IOMAP_WRITE_F_UNSHARE = (1 << 0), > +}; > + > static void > iomap_write_failed(struct inode *inode, loff_t pos, unsigned len) > { > @@ -562,7 +566,7 @@ iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff, > } > > static int > -__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, > +__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags, > struct page *page, struct iomap *iomap) > { > struct iomap_page *iop = iomap_page_create(inode, page); > @@ -581,11 +585,14 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, > if (plen == 0) > break; > > - if ((from <= poff || from >= poff + plen) && > + if (!(flags & IOMAP_WRITE_F_UNSHARE) && Mmm, archeology of code that I wrote originally and have forgotten already... :) I think the purpose of F_UNSHARE is to mimic the behavior of the code that's being removed, and the old behavior is that if a user asks to unshare a page backed by shared extents we'll read in all the blocks backing the page, even if that means reading in blocks that weren't part of the original unshare request, right? The only reason I can think of (or remember) for doing it that way is that read_mapping_page does its IO one page at a time, i.e. sheer laziness on my part. So do we actually need F_UNSHARE to read in the whole page or can we get by with reading only the blocks that are included in the range that's being unshared, just like how write only reads in the blocks that are included in the range being written to? --D > + (from <= poff || from >= poff + plen) && > (to <= poff || to >= poff + plen)) > continue; > > if (iomap_block_needs_zeroing(inode, iomap, block_start)) { > + if (WARN_ON_ONCE(flags & IOMAP_WRITE_F_UNSHARE)) > + return -EIO; > zero_user_segments(page, poff, from, to, poff + plen); > iomap_set_range_uptodate(page, poff, plen); > continue; > @@ -631,7 +638,8 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags, > else if (iomap->flags & IOMAP_F_BUFFER_HEAD) > status = __block_write_begin_int(page, pos, len, NULL, iomap); > else > - status = __iomap_write_begin(inode, pos, len, page, iomap); > + status = __iomap_write_begin(inode, pos, len, flags, page, > + iomap); > > if (unlikely(status)) > goto out_unlock; > @@ -854,22 +862,6 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter, > } > EXPORT_SYMBOL_GPL(iomap_file_buffered_write); > > -static struct page * > -__iomap_read_page(struct inode *inode, loff_t offset) > -{ > - struct address_space *mapping = inode->i_mapping; > - struct page *page; > - > - page = read_mapping_page(mapping, offset >> PAGE_SHIFT, NULL); > - if (IS_ERR(page)) > - return page; > - if (!PageUptodate(page)) { > - put_page(page); > - return ERR_PTR(-EIO); > - } > - return page; > -} > - > static loff_t > iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > struct iomap *iomap) > @@ -885,24 +877,15 @@ iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > return length; > > do { > - struct page *page, *rpage; > - unsigned long offset; /* Offset into pagecache page */ > - unsigned long bytes; /* Bytes to write to page */ > - > - offset = offset_in_page(pos); > - bytes = min_t(loff_t, PAGE_SIZE - offset, length); > - > - rpage = __iomap_read_page(inode, pos); > - if (IS_ERR(rpage)) > - return PTR_ERR(rpage); > + unsigned long offset = offset_in_page(pos); > + unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length); > + struct page *page; > > - status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap); > - put_page(rpage); > + status = iomap_write_begin(inode, pos, bytes, > + IOMAP_WRITE_F_UNSHARE, &page, iomap); > if (unlikely(status)) > return status; > > - WARN_ON_ONCE(!PageUptodate(page)); > - > status = iomap_write_end(inode, pos, bytes, bytes, page, iomap); > if (unlikely(status <= 0)) { > if (WARN_ON_ONCE(status == 0)) > -- > 2.20.1 >
On Mon, Sep 16, 2019 at 11:34:28AM -0700, Darrick J. Wong wrote: > > - if ((from <= poff || from >= poff + plen) && > > + if (!(flags & IOMAP_WRITE_F_UNSHARE) && > > Mmm, archeology of code that I wrote originally and have forgotten > already... :) > > I think the purpose of F_UNSHARE is to mimic the behavior of the code > that's being removed, and the old behavior is that if a user asks to > unshare a page backed by shared extents we'll read in all the blocks > backing the page, even if that means reading in blocks that weren't part > of the original unshare request, right? No. The flag causes the code to always read the page, even if the iomap range covers the whole block. For normal writes that means we don't to read the block in at all, but for unshare we absolutely must do so.
On Mon, Sep 30, 2019 at 01:07:31PM +0200, Christoph Hellwig wrote: > On Mon, Sep 16, 2019 at 11:34:28AM -0700, Darrick J. Wong wrote: > > > - if ((from <= poff || from >= poff + plen) && > > > + if (!(flags & IOMAP_WRITE_F_UNSHARE) && > > > > Mmm, archeology of code that I wrote originally and have forgotten > > already... :) > > > > I think the purpose of F_UNSHARE is to mimic the behavior of the code > > that's being removed, and the old behavior is that if a user asks to > > unshare a page backed by shared extents we'll read in all the blocks > > backing the page, even if that means reading in blocks that weren't part > > of the original unshare request, right? > > No. The flag causes the code to always read the page, even if the iomap > range covers the whole block. For normal writes that means we don't to > read the block in at all, but for unshare we absolutely must do so. Ahhh, right. Missed that. I'll go RVB the v2 patch now. --D
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index fe099faf540f..a421977a9496 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -533,6 +533,10 @@ iomap_migrate_page(struct address_space *mapping, struct page *newpage, EXPORT_SYMBOL_GPL(iomap_migrate_page); #endif /* CONFIG_MIGRATION */ +enum { + IOMAP_WRITE_F_UNSHARE = (1 << 0), +}; + static void iomap_write_failed(struct inode *inode, loff_t pos, unsigned len) { @@ -562,7 +566,7 @@ iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff, } static int -__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, +__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags, struct page *page, struct iomap *iomap) { struct iomap_page *iop = iomap_page_create(inode, page); @@ -581,11 +585,14 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, if (plen == 0) break; - if ((from <= poff || from >= poff + plen) && + if (!(flags & IOMAP_WRITE_F_UNSHARE) && + (from <= poff || from >= poff + plen) && (to <= poff || to >= poff + plen)) continue; if (iomap_block_needs_zeroing(inode, iomap, block_start)) { + if (WARN_ON_ONCE(flags & IOMAP_WRITE_F_UNSHARE)) + return -EIO; zero_user_segments(page, poff, from, to, poff + plen); iomap_set_range_uptodate(page, poff, plen); continue; @@ -631,7 +638,8 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags, else if (iomap->flags & IOMAP_F_BUFFER_HEAD) status = __block_write_begin_int(page, pos, len, NULL, iomap); else - status = __iomap_write_begin(inode, pos, len, page, iomap); + status = __iomap_write_begin(inode, pos, len, flags, page, + iomap); if (unlikely(status)) goto out_unlock; @@ -854,22 +862,6 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter, } EXPORT_SYMBOL_GPL(iomap_file_buffered_write); -static struct page * -__iomap_read_page(struct inode *inode, loff_t offset) -{ - struct address_space *mapping = inode->i_mapping; - struct page *page; - - page = read_mapping_page(mapping, offset >> PAGE_SHIFT, NULL); - if (IS_ERR(page)) - return page; - if (!PageUptodate(page)) { - put_page(page); - return ERR_PTR(-EIO); - } - return page; -} - static loff_t iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap *iomap) @@ -885,24 +877,15 @@ iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data, return length; do { - struct page *page, *rpage; - unsigned long offset; /* Offset into pagecache page */ - unsigned long bytes; /* Bytes to write to page */ - - offset = offset_in_page(pos); - bytes = min_t(loff_t, PAGE_SIZE - offset, length); - - rpage = __iomap_read_page(inode, pos); - if (IS_ERR(rpage)) - return PTR_ERR(rpage); + unsigned long offset = offset_in_page(pos); + unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length); + struct page *page; - status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap); - put_page(rpage); + status = iomap_write_begin(inode, pos, bytes, + IOMAP_WRITE_F_UNSHARE, &page, iomap); if (unlikely(status)) return status; - WARN_ON_ONCE(!PageUptodate(page)); - status = iomap_write_end(inode, pos, bytes, bytes, page, iomap); if (unlikely(status <= 0)) { if (WARN_ON_ONCE(status == 0))
Use the existing iomap write_begin code to read the pages unshared by iomap_file_unshare. That avoids the extra ->readpage call and extent tree lookup currently done by read_mapping_page. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/iomap/buffered-io.c | 49 ++++++++++++++---------------------------- 1 file changed, 16 insertions(+), 33 deletions(-)