linux-kernel - [PATCH] mm/slab.c: micro-optimization spare one branch in main flow

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Date:   Wed, 16 Sep 2020 22:05:39 +0200
From:   mateusznosek0@...il.com
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Mateusz Nosek <mateusznosek0@...il.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org
Subject: [PATCH] mm/slab.c: micro-optimization spare one branch in main flow

From: Mateusz Nosek <mateusznosek0@...il.com>

By small refactoring two 'unlikely' branches are changed so that if
not one of them is true then only one branch occurs in 'likely' path
of the function in question. Change verified in assembly generated
by gcc 8.3.0.

Signed-off-by: Mateusz Nosek <mateusznosek0@...il.com>
---
 mm/slab.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 2cb494d98fe9..e04ea756bcbc 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4186,9 +4186,10 @@ size_t __ksize(const void *objp)
 	struct kmem_cache *c;
 	size_t size;
 
-	BUG_ON(!objp);
-	if (unlikely(objp == ZERO_SIZE_PTR))
+	if (unlikely(ZERO_OR_NULL_PTR(objp))) {
+		BUG_ON(!objp);
 		return 0;
+	}
 
 	c = virt_to_cache(objp);
 	size = c ? c->object_size : 0;
-- 
2.20.1