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bio: don't copy bvec for direct IO

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The block layer spends quite a while in blkdev_direct_IO() to copy and
initialise bio's bvec. However, if we've already got a bvec in the input
iterator it might be reused in some cases, i.e. when new
ITER_BVEC_FLAG_FIXED flag is set. Simple tests show considerable
performance boost, and it also reduces memory footprint.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov
2021-01-09 16:03:03 +00:00
committed by Jens Axboe
parent 3e1a88ec96
commit c42bca92be
3 changed files with 40 additions and 37 deletions
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9
Documentation/filesystems/porting.rst
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@@ -872,3 +872,12 @@ its result is kern_unmount() or kern_unmount_array().
zero-length bvec segments are disallowed, they must be filtered out before
passed on to an iterator.
---
**mandatory**
For bvec based itererators bio_iov_iter_get_pages() now doesn't copy bvecs but
uses the one provided. Anyone issuing kiocb-I/O should ensure that the bvec and
page references stay until I/O has completed, i.e. until ->ki_complete() has
been called or returned with non -EIOCBQUEUED code.