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Subject[PATCH v3 3/7] block/psi: remove PSI annotations from direct IO
Date
Direct IO does not operate on the current working set of pages managed
by the kernel, so it should not be accounted as memory stall to PSI
infrastructure.

The block layer and iomap direct IO use bio_iov_iter_get_pages()
to build bios, and they are the only users of it, so to avoid PSI
tracking for them clear out BIO_WORKINGSET flag. Do same for
dio_bio_submit() because fs/direct_io constructs bios by hand directly
calling bio_add_page().

Reported-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
block/bio.c | 6 ++++++
fs/direct-io.c | 2 ++
2 files changed, 8 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index 1f2cc1fbe283..9f26984af643 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1099,6 +1099,9 @@ 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's intended for direct IO, so doesn't do PSI tracking, the caller is
+ * responsible for setting BIO_WORKINGSET if necessary.
*/
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
@@ -1123,6 +1126,9 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)

if (is_bvec)
bio_set_flag(bio, BIO_NO_PAGE_REF);
+
+ /* don't account direct I/O as memory stall */
+ bio_clear_flag(bio, BIO_WORKINGSET);
return bio->bi_vcnt ? 0 : ret;
}
EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
diff --git a/fs/direct-io.c b/fs/direct-io.c
index d53fa92a1ab6..0e689233f2c7 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;
+ /* don't account direct I/O as memory stall */
+ bio_clear_flag(bio, BIO_WORKINGSET);

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