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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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5
include/linux/bio.h
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@@ -444,10 +444,13 @@ static inline void bio_wouldblock_error(struct bio *bio)
/*
* Calculate number of bvec segments that should be allocated to fit data
* pointed by @iter.
* pointed by @iter. If @iter is backed by bvec it's going to be reused
* instead of allocating a new one.
*/
static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
{
if (iov_iter_is_bvec(iter))
return 0;
return iov_iter_npages(iter, max_segs);
}