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 <wi...@infradead.org>
[BIO_WORKINGSET] Suggested-by: Johannes Weiner <han...@cmpxchg.org>
Signed-off-by: Pavel Begunkov <asml.sile...@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
