linux-kernel - [PATCH 02/17] iomap: Protect read_bytes_pending with the state

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Date:   Fri, 15 Sep 2023 19:36:52 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        torvalds@...ux-foundation.org, Nicholas Piggin <npiggin@...il.com>
Subject: [PATCH 02/17] iomap: Protect read_bytes_pending with the state_lock

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

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.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