[PATCH v1 4/6] block/psi: remove PSI annotations from direct IO

Pavel Begunkov
2020-12-15T00:28:09Z

As reported, we must not do pressure stall information accounting for
direct IO, because otherwise it tells that it's thrashing a page when
actually doing IO on hot data.

Apparently, bio_iov_iter_get_pages() is used only by paths doing direct
IO, so just make it avoid setting BIO_WORKINGSET, it also saves us CPU
cycles on doing that. For fs/direct-io.c just clear the flag before
submit_bio(), it's not of much concern performance-wise.

Reported-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
block/bio.c | 25 ++++++++++++++++---------
fs/direct-io.c | 2 ++
2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4a8f77bb3956..3192358c411f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -963,18 +963,22 @@ EXPORT_SYMBOL_GPL(bio_release_pages);
static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
{
const struct bio_vec *bv = iter->bvec;
- unsigned int len;
- size_t size;
+ struct page *page = bv->bv_page;
+ bool same_page = false;
+ unsigned int off, len;

if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
return -EINVAL;

len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
- size = bio_add_page(bio, bv->bv_page, len,
- bv->bv_offset + iter->iov_offset);
- if (unlikely(size != len))
- return -EINVAL;
- iov_iter_advance(iter, size);
+ off = bv->bv_offset + iter->iov_offset;
+
+ if (!__bio_try_merge_page(bio, page, len, off, &same_page)) {
+ if (bio_full(bio, len))
+ return -EINVAL;
+ bio_add_page_noaccount(bio, page, len, off);
+ }
+ iov_iter_advance(iter, len);
return 0;
}

@@ -1023,8 +1027,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
put_page(page);
} else {
if (WARN_ON_ONCE(bio_full(bio, len)))
- return -EINVAL;
- __bio_add_page(bio, page, len, offset);
+ return -EINVAL;
+ bio_add_page_noaccount(bio, page, len, offset);
}
offset = 0;
}
@@ -1099,6 +1103,9 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
* fit into the bio, or are requested in @iter, whatever is smaller. If
* MM encounters an error pinning the requested pages, it stops. Error
* is returned only if 0 pages could be pinned.
+ *
+ * It also doesn't set BIO_WORKINGSET, so is intended for direct IO. If used
+ * otherwise the caller is responsible to do that to keep PSI happy.
*/
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
diff --git a/fs/direct-io.c b/fs/direct-io.c
index d53fa92a1ab6..914a7f600ecd 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -426,6 +426,8 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
unsigned long flags;

bio->bi_private = dio;
+ /* PSI is only for paging IO */
+ bio_clear_flag(bio, BIO_WORKINGSET);

spin_lock_irqsave(&dio->bio_lock, flags);
dio->refcount++;
--
2.24.0