From: Filipe Manana <fdmanana@suse.com>
Date: Wed, 11 Mar 2026 15:07:11 +0000 (+0000)
Subject: btrfs: avoid unnecessary wake ups on io trees when there are no waiters
X-Git-Tag: v7.1-rc1~231^2~39
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=87f5c3139ee34e0642584cff86298ef4b9a827ef;p=thirdparty%2Fkernel%2Flinux.git

btrfs: avoid unnecessary wake ups on io trees when there are no waiters

Whenever clearing the extent lock bits of an extent state record, we
unconditionally call wake_up() on the state's waitqueue. Most of the
time there are no waiters on the queue so we are just wasting time calling
wake_up(), since that requires locking and unlocking the queue's spinlock,
disable and re-enable interrupts, function calls, and other minor overhead
while we are holding a critical section delimited by the extent io tree's
spinlock.

So call wake_up() only if there are waiters on an extent state's wait
queue.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---

diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c
index 5ffb99c258e9a..0d9437e72bd4f 100644
--- a/fs/btrfs/extent-io-tree.c
+++ b/fs/btrfs/extent-io-tree.c
@@ -536,6 +536,24 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
 	return 0;
 }
 
+static inline void state_wake_up(struct extent_io_tree *tree,
+				 struct extent_state *state, u32 bits)
+{
+	lockdep_assert_held(&tree->lock);
+
+	if (!(bits & EXTENT_LOCK_BITS))
+		return;
+
+	/*
+	 * No memory barriers because the tree's lock is held while:
+	 *
+	 * 1) Adding waiters to the queue.
+	 * 2) Waking up waiters.
+	 * 3) Removing waiters from queue.
+	 */
+	cond_wake_up_nomb(&state->wq);
+}
+
 /*
  * Use this during tree iteration to avoid doing next node searches when it's
  * not needed (the current record ends at or after the target range's end).
@@ -571,8 +589,7 @@ static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
 	if (unlikely(ret))
 		extent_io_tree_panic(tree, state, "add_extent_changeset", ret);
 	state->state &= ~bits_to_clear;
-	if (bits & EXTENT_LOCK_BITS)
-		wake_up(&state->wq);
+	state_wake_up(tree, state, bits);
 	if (state->state == 0) {
 		next = next_search_state(state, end);
 		if (extent_state_in_tree(state)) {
@@ -618,7 +635,6 @@ int btrfs_clear_extent_bit_changeset(struct extent_io_tree *tree, u64 start, u64
 	u64 last_end;
 	int ret = 0;
 	bool clear;
-	bool wake;
 	const bool delete = (bits & EXTENT_CLEAR_ALL_BITS);
 	gfp_t mask;
 
@@ -632,7 +648,6 @@ int btrfs_clear_extent_bit_changeset(struct extent_io_tree *tree, u64 start, u64
 	if (bits & EXTENT_DELALLOC)
 		bits |= EXTENT_NORESERVE;
 
-	wake = (bits & EXTENT_LOCK_BITS);
 	clear = (bits & (EXTENT_LOCK_BITS | EXTENT_BOUNDARY));
 again:
 	if (!prealloc) {
@@ -758,8 +773,7 @@ hit_next:
 			state->start = end + 1;
 			state->end = orig_end;
 
-			if (wake)
-				wake_up(&state->wq);
+			state_wake_up(tree, state, bits);
 			goto out;
 		}
 
@@ -773,8 +787,7 @@ hit_next:
 			goto out;
 		}
 
-		if (wake)
-			wake_up(&state->wq);
+		state_wake_up(tree, state, bits);
 
 		clear_state_bit(tree, prealloc, bits, end, changeset);