commit 46e700abc44ce215acb4341d9702ce3972eda571
author Mel Gorman <mgorman@techsingularity.net> Fri Nov 06 16:28:15 2015 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> Fri Nov 06 17:50:42 2015 -0800
tree 6730677333bd4a69a014cf87fc6e40207b8cab1c
parent c9ab0c4fbeb0202bac3548378a977e1536ebe3ca

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@techsingularity.net>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cpuset.h

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 5a13119..85a868c 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -104,6 +104,9 @@
  */
 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 bool read_mems_allowed_retry(unsigned int seq)
 {
+	if (!cpusets_enabled())
+		return false;
+
 	return read_seqcount_retry(&current->mems_allowed_seq, seq);
 }