dm writecache: add unlikely for getting two block with same LBA

[Huaisheng Ye]

From: Huaisheng Ye <yehs1@xxxxxxxxxx>

In function writecache_writeback, entries g and f has same original
sector only happens at entry f has been committed, but entry g has
NOT yet.

The probability of this happening is very low in the following
 256 blocks at most of entry e, so add unlikely for the result.

Signed-off-by: Huaisheng Ye <yehs1@xxxxxxxxxx>
---
 drivers/md/dm-writecache.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 5c7009d..3643084 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -1628,8 +1628,8 @@ static void writecache_writeback(struct work_struct *work)
 			if (unlikely(!next_node))
 				break;
 			g = container_of(next_node, struct wc_entry, rb_node);
-			if (read_original_sector(wc, g) ==
-			    read_original_sector(wc, f)) {
+			if (unlikely(read_original_sector(wc, g) ==
+			    read_original_sector(wc, f))) {
 				f = g;
 				continue;
 			}
-- 
1.8.3.1