From: Filipe Manana <fdmanana@suse.com>
Date: Mon, 2 Jun 2025 12:46:23 +0000 (+0100)
Subject: btrfs: add comment for optimization in free_extent_buffer()
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=2697b6159744e5afae0f7715da9f830ba6f9e45a;p=users%2Fjedix%2Flinux-maple.git

btrfs: add comment for optimization in free_extent_buffer()

There's this special atomic compare and exchange logic which serves to
avoid locking the extent buffers refs_lock spinlock and therefore reduce
lock contention, so add a comment to make it more obvious.

Reviewed-by: Boris Burkov <boris@bur.io>
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.c b/fs/btrfs/extent_io.c
index 21d2cb7f538e..5e8dd9a99e58 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3493,6 +3493,7 @@ void free_extent_buffer(struct extent_buffer *eb)
 			break;
 		}
 
+		/* Optimization to avoid locking eb->refs_lock. */
 		if (atomic_try_cmpxchg(&eb->refs, &refs, refs - 1))
 			return;
 	}