linux-kernel - [PATCH] dm-writecache: add unlikely for returned value of rb

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Message-Id: <20190412152814.27158-1-huye@redhat.com>
Date:   Fri, 12 Apr 2019 11:28:14 -0400
From:   Huaisheng Ye <huye@...hat.com>
To:     mpatocka@...hat.com, snitzer@...hat.com, agk@...hat.com
Cc:     prarit@...hat.com, chengnt@...ovo.com, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org, Huaisheng Ye <yehs1@...ovo.com>
Subject: [PATCH] dm-writecache: add unlikely for returned value of rb_next/prev

From: Huaisheng Ye <yehs1@...ovo.com>

In functions writecache_discard and writecache_find_entry, there is
high probablity that the pointer of structure rb_node doesn't equal
to NULL. Add unlikly for the pointer node.

Signed-off-by: Huaisheng Ye <yehs1@...ovo.com>
---
 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 5b4d1c1..cfbbfbc 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -571,7 +571,7 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
 			node = rb_prev(&e->rb_node);
 		else
 			node = rb_next(&e->rb_node);
-		if (!node)
+		if (unlikely(!node))
 			return e;
 		e2 = container_of(node, struct wc_entry, rb_node);
 		if (read_original_sector(wc, e2) != block)
@@ -804,7 +804,7 @@ static void writecache_discard(struct dm_writecache *wc, sector_t start, sector_
 			writecache_free_entry(wc, e);
 		}
 
-		if (!node)
+		if (unlikely(!node))
 			break;
 
 		e = container_of(node, struct wc_entry, rb_node);
-- 
1.8.3.1