linux-kernel - [PATCH 03/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

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Message-Id: <1442832762-7247-4-git-send-email-mgorman@techsingularity.net>
Date:	Mon, 21 Sep 2015 11:52:35 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 03/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

There is a seqcounter that protects against spurious allocation failures
when a task is changing the allowed nodes in a cpuset. There is no need
to check the seqcounter until a cpuset exists.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
Acked-by: Christoph Lameter <cl@...ux.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/cpuset.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b357997cac5..6eb27cb480b7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct task_struct *p);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
+	if (!cpusets_enabled())
+		return 0;
+
 	return read_seqcount_begin(&current->mems_allowed_seq);
 }
 
@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
+	if (!cpusets_enabled())
+		return false;
+
 	return read_seqcount_retry(&current->mems_allowed_seq, seq);
 }
 
-- 
2.4.6

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