[PATCH 2/2] block: no-copy bvec for direct IO
From: Pavel Begunkov <asml.silence@gmail.com>
Date: 2020-12-09 02:24:53
Also in:
io-uring, linux-fsdevel, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
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> [BIO_WORKINGSET] Suggested-by: Johannes Weiner [off-list ref] Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- fs/block_dev.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index d699f3af1a09..aee5d2e4f324 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c@@ -349,6 +349,28 @@ static void blkdev_bio_end_io(struct bio *bio) } } +static int bio_iov_fixed_bvec_get_pages(struct bio *bio, struct iov_iter *iter) +{ + bio->bi_vcnt = iter->nr_segs; + bio->bi_max_vecs = iter->nr_segs; + bio->bi_io_vec = (struct bio_vec *)iter->bvec; + bio->bi_iter.bi_bvec_done = iter->iov_offset; + bio->bi_iter.bi_size = iter->count; + + /* + * In practice groups of pages tend to be accessed/reclaimed/refaulted + * together. To not go over bvec for those who didn't set BIO_WORKINGSET + * approximate it by looking at the first page and inducing it to the + * whole bio + */ + if (unlikely(PageWorkingset(iter->bvec->bv_page))) + bio_set_flag(bio, BIO_WORKINGSET); + bio_set_flag(bio, BIO_NO_PAGE_REF); + + iter->count = 0; + return 0; +} + static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_vecs) {
@@ -368,6 +390,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_vecs) (bdev_logical_block_size(bdev) - 1)) return -EINVAL; + if (iov_iter_bvec_fixed(iter)) + nr_vecs = 0; bio = bio_alloc_bioset(GFP_KERNEL, nr_vecs, &blkdev_dio_pool); dio = container_of(bio, struct blkdev_dio, bio);
@@ -398,7 +422,11 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_vecs) bio->bi_end_io = blkdev_bio_end_io; bio->bi_ioprio = iocb->ki_ioprio; - ret = bio_iov_iter_get_pages(bio, iter); + if (iov_iter_is_bvec(iter) && iov_iter_bvec_fixed(iter)) + ret = bio_iov_fixed_bvec_get_pages(bio, iter); + else + ret = bio_iov_iter_get_pages(bio, iter); + if (unlikely(ret)) { bio->bi_status = BLK_STS_IOERR; bio_endio(bio);
--
2.24.0