[PATCH 02/17] iomap: Protect read_bytes_pending with the state_lock

Matthew Wilcox (Oracle)
2023-09-15T18:38:19Z

Perform one atomic operation (acquiring the spinlock) instead of
two (spinlock & atomic_sub) per read completion.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/iomap/buffered-io.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 4c05fd457ee7..cade15b70627 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -29,9 +29,9 @@ typedef int (*iomap_punch_t)(struct inode *inode, loff_t offset, loff_t length);
* and I/O completions.
*/
struct iomap_folio_state {
- atomic_t read_bytes_pending;
- atomic_t write_bytes_pending;
spinlock_t state_lock;
+ unsigned int read_bytes_pending;
+ atomic_t write_bytes_pending;

/*
* Each block has two bits in this bitmap:
@@ -183,7 +183,7 @@ static void ifs_free(struct folio *folio)

if (!ifs)
return;
- WARN_ON_ONCE(atomic_read(&ifs->read_bytes_pending));
+ WARN_ON_ONCE(ifs->read_bytes_pending != 0);
WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending));
WARN_ON_ONCE(ifs_is_fully_uptodate(folio, ifs) !=
folio_test_uptodate(folio));
@@ -250,19 +250,33 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
*lenp = plen;
}

-static void iomap_finish_folio_read(struct folio *folio, size_t offset,
+static void iomap_finish_folio_read(struct folio *folio, size_t off,
size_t len, int error)
{
struct iomap_folio_state *ifs = folio->private;
+ unsigned long flags;
+ bool uptodate;
+ bool finished = true;
+
+ if (ifs)
+ spin_lock_irqsave(&ifs->state_lock, flags);

if (unlikely(error)) {
- folio_clear_uptodate(folio);
+ uptodate = false;
folio_set_error(folio);
} else {
- iomap_set_range_uptodate(folio, offset, len);
+ uptodate = !ifs || ifs_set_range_uptodate(folio, ifs, off, len);
}

- if (!ifs || atomic_sub_and_test(len, &ifs->read_bytes_pending))
+ if (ifs) {
+ ifs->read_bytes_pending -= len;
+ finished = !ifs->read_bytes_pending;
+ spin_unlock_irqrestore(&ifs->state_lock, flags);
+ }
+
+ if (uptodate)
+ folio_mark_uptodate(folio);
+ if (finished)
folio_unlock(folio);
}

@@ -360,8 +374,11 @@ static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
}

ctx->cur_folio_in_bio = true;
- if (ifs)
- atomic_add(plen, &ifs->read_bytes_pending);
+ if (ifs) {
+ spin_lock_irq(&ifs->state_lock);
+ ifs->read_bytes_pending += plen;
+ spin_unlock_irq(&ifs->state_lock);
+ }

sector = iomap_sector(iomap, pos);
if (!ctx->bio ||
--
2.40.1