mm, page_alloc: remove unnecessary taking of a seqlock when cpusets are disabled

gormanm · torvalds · commit 46e700abc44c · 2015-11-06T17:50:42.000-08:00
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 &lt;mgorman@techsingularity.net&gt;
Acked-by: Christoph Lameter &lt;cl@linux.com&gt;
Acked-by: David Rientjes &lt;rientjes@google.com&gt;
Acked-by: Vlastimil Babka &lt;vbabka@suse.cz&gt;
Acked-by: Michal Hocko &lt;mhocko@suse.com&gt;
Acked-by: Johannes Weiner &lt;hannes@cmpxchg.org&gt;
Cc: Vitaly Wool &lt;vitalywool@gmail.com&gt;
Cc: Rik van Riel &lt;riel@redhat.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
@@ -104,6 +104,9 @@ extern void cpuset_print_current_mems_allowed(void);
  */
 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);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -104,6 +104,9 @@ extern void cpuset_print_current_mems_allowed(void);`
`104`	`104`	`*/`
`105`	`105`	`static inline unsigned int read_mems_allowed_begin(void)`
`106`	`106`	`{`
	`107`	`+ if (!cpusets_enabled())`
	`108`	`+ return 0;`
	`109`	`+`
`107`	`110`	`return read_seqcount_begin(&current->mems_allowed_seq);`
`108`	`111`	`}`
`109`	`112`
`@@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)`
`115`	`118`	`*/`
`116`	`119`	`static inline bool read_mems_allowed_retry(unsigned int seq)`
`117`	`120`	`{`
	`121`	`+ if (!cpusets_enabled())`
	`122`	`+ return false;`
	`123`	`+`
`118`	`124`	`return read_seqcount_retry(&current->mems_allowed_seq, seq);`
`119`	`125`	`}`
`120`	`126`