| Message ID | 20200319150720.24622-1-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iomap: Submit BIOs at the end of each extent | expand |
On Thu, Mar 19, 2020 at 08:07:20AM -0700, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > By definition, an extent covers a range of consecutive blocks, so > it would be quite rare to be able to just add pages to the BIO from > a previous range. The only case we can think of is a mapped extent > followed by a hole extent, followed by another mapped extent which has > been allocated immediately after the first extent. We believe this to Well... userspace can induce that with fallocate(INSERT_RANGE). :) > be an unlikely layout for a filesystem to choose and, since the queue > is plugged, those two BIOs would be merged by the block layer. > > The reason we care is that ext2/ext4 choose to lay out blocks 0-11 > consecutively, followed by the indirect block, and we want to merge those > two BIOs. If we don't submit the data BIO before asking the filesystem > for the next extent, then the indirect BIO will be submitted first, > and waited for, leading to inefficient I/O patterns. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > fs/iomap/buffered-io.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index 83438b3257de..8d26920ddf00 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -388,6 +388,11 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length, > ctx, iomap, srcmap); > } > > + if (ctx->bio) { > + submit_bio(ctx->bio); > + ctx->bio = NULL; > + } Makes sense, but could we have a quick comment here to capture why we're submitting the bio here? /* * Submit the bio now so that we neither combine IO requests for * non-adjacent ranges nor interleave data and metadata requests. */ --D > + > return done; > } > > -- > 2.25.1 >
On Thu, Mar 19, 2020 at 08:18:19AM -0700, Darrick J. Wong wrote: > On Thu, Mar 19, 2020 at 08:07:20AM -0700, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > By definition, an extent covers a range of consecutive blocks, so > > it would be quite rare to be able to just add pages to the BIO from > > a previous range. The only case we can think of is a mapped extent > > followed by a hole extent, followed by another mapped extent which has > > been allocated immediately after the first extent. We believe this to > > Well... userspace can induce that with fallocate(INSERT_RANGE). :) It's not impossible, of course ... just unlikely. Nobody actually uses INSERT_RANGE anyway. > > be an unlikely layout for a filesystem to choose and, since the queue > > is plugged, those two BIOs would be merged by the block layer. > > > > The reason we care is that ext2/ext4 choose to lay out blocks 0-11 > > consecutively, followed by the indirect block, and we want to merge those > > two BIOs. If we don't submit the data BIO before asking the filesystem > > for the next extent, then the indirect BIO will be submitted first, > > and waited for, leading to inefficient I/O patterns. > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > --- > > fs/iomap/buffered-io.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > index 83438b3257de..8d26920ddf00 100644 > > --- a/fs/iomap/buffered-io.c > > +++ b/fs/iomap/buffered-io.c > > @@ -388,6 +388,11 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length, > > ctx, iomap, srcmap); > > } > > > > + if (ctx->bio) { > > + submit_bio(ctx->bio); > > + ctx->bio = NULL; > > + } > > Makes sense, but could we have a quick comment here to capture why we're > submitting the bio here? > > /* > * Submit the bio now so that we neither combine IO requests for > * non-adjacent ranges nor interleave data and metadata requests. > */ How about: * Submitting the bio here leads to better I/O patterns for * filesystems which need to do metadata reads to find the * next range. I also realised we can add: @@ -454,8 +459,6 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, } ret = 0; done: - if (ctx.bio) - submit_bio(ctx.bio); if (ctx.cur_page) { if (!ctx.cur_page_in_bio) unlock_page(ctx.cur_page); since we always subit the bio in readpages_actor.
On Thu, Mar 19, 2020 at 12:06:46PM -0700, Matthew Wilcox wrote: > On Thu, Mar 19, 2020 at 08:18:19AM -0700, Darrick J. Wong wrote: > > On Thu, Mar 19, 2020 at 08:07:20AM -0700, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > > > By definition, an extent covers a range of consecutive blocks, so > > > it would be quite rare to be able to just add pages to the BIO from > > > a previous range. The only case we can think of is a mapped extent > > > followed by a hole extent, followed by another mapped extent which has > > > been allocated immediately after the first extent. We believe this to > > > > Well... userspace can induce that with fallocate(INSERT_RANGE). :) > > It's not impossible, of course ... just unlikely. Nobody actually uses > INSERT_RANGE anyway. > > > > be an unlikely layout for a filesystem to choose and, since the queue > > > is plugged, those two BIOs would be merged by the block layer. > > > > > > The reason we care is that ext2/ext4 choose to lay out blocks 0-11 > > > consecutively, followed by the indirect block, and we want to merge those > > > two BIOs. If we don't submit the data BIO before asking the filesystem > > > for the next extent, then the indirect BIO will be submitted first, > > > and waited for, leading to inefficient I/O patterns. > > > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > > --- > > > fs/iomap/buffered-io.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > > index 83438b3257de..8d26920ddf00 100644 > > > --- a/fs/iomap/buffered-io.c > > > +++ b/fs/iomap/buffered-io.c > > > @@ -388,6 +388,11 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length, > > > ctx, iomap, srcmap); > > > } > > > > > > + if (ctx->bio) { > > > + submit_bio(ctx->bio); > > > + ctx->bio = NULL; > > > + } > > > > Makes sense, but could we have a quick comment here to capture why we're > > submitting the bio here? > > > > /* > > * Submit the bio now so that we neither combine IO requests for > > * non-adjacent ranges nor interleave data and metadata requests. > > */ > > How about: > > * Submitting the bio here leads to better I/O patterns for > * filesystems which need to do metadata reads to find the > * next range. Oooh I like your version better. > I also realised we can add: > > @@ -454,8 +459,6 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, > } > ret = 0; > done: > - if (ctx.bio) > - submit_bio(ctx.bio); > if (ctx.cur_page) { > if (!ctx.cur_page_in_bio) > unlock_page(ctx.cur_page); > > since we always subit the bio in readpages_actor. <nod> I'll keep an eye out for v2. :) --D
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 83438b3257de..8d26920ddf00 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -388,6 +388,11 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length, ctx, iomap, srcmap); } + if (ctx->bio) { + submit_bio(ctx->bio); + ctx->bio = NULL; + } + return done; }