linux-kernel - [patch] mm: memcontrol: micro-optimize mem_cgroup_update_page

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Message-Id: <1413818259-10913-1-git-send-email-hannes@cmpxchg.org>
Date:	Mon, 20 Oct 2014 11:17:39 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [patch] mm: memcontrol: micro-optimize mem_cgroup_update_page_stat()

Do not look up the page_cgroup when the memory controller is
runtime-disabled, but do assert that the locking protocol is followed
under DEBUG_VM regardless.  Also remove the unused flags variable.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 76892eb89d26..bea3fddb3372 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2177,13 +2177,14 @@ void mem_cgroup_update_page_stat(struct page *page,
 				 enum mem_cgroup_stat_index idx, int val)
 {
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc = lookup_page_cgroup(page);
-	unsigned long uninitialized_var(flags);
+	struct page_cgroup *pc;
+
+	VM_BUG_ON(!rcu_read_lock_held());
 
 	if (mem_cgroup_disabled())
 		return;
 
-	VM_BUG_ON(!rcu_read_lock_held());
+	pc = lookup_page_cgroup(page);
 	memcg = pc->mem_cgroup;
 	if (unlikely(!memcg || !PageCgroupUsed(pc)))
 		return;
-- 
2.1.2

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