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Commit 5407a562 authored by Phil Carmody's avatar Phil Carmody Committed by Linus Torvalds
Browse files

mm: remove unnecessary use of atomic 

The bottom 4 hunks are atomically changing memory to which there are no
aliases as it's freshly allocated, so there's no need to use atomic
operations.

The other hunks are just atomic_read and atomic_set, and do not involve
any read-modify-write.  The use of atomic_{read,set} doesn't prevent a
read/write or write/write race, so if a race were possible (I'm not saying
one is), then it would still be there even with atomic_set.

See:
http://digitalvampire.org/blog/index.php/2007/05/13/atomic-cargo-cults/



Signed-off-by: default avatarPhil Carmody <ext-phil.2.carmody@nokia.com>
Acked-by: default avatarKirill A. Shutemov <kirill@shutemov.name>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent df64f81b

mm/memcontrol.c

+7 −7
Original line number Diff line number Diff line
@@ -152,7 +152,7 @@ struct mem_cgroup_threshold { 
/* For threshold */

struct mem_cgroup_threshold_ary {

	/* An array index points to threshold just below usage. */

	atomic_t current_threshold;

	int current_threshold;

	/* Size of entries[] */

	unsigned int size;

	/* Array of thresholds */
@@ -3412,7 +3412,7 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap) 
	 * If it's not true, a threshold was crossed after last

	 * call of __mem_cgroup_threshold().

	 */

	i = atomic_read(&t->current_threshold);

	i = t->current_threshold;



	/*

	 * Iterate backward over array of thresholds starting from
@@ -3436,7 +3436,7 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap) 
		eventfd_signal(t->entries[i].eventfd, 1);



	/* Update current_threshold */

	atomic_set(&t->current_threshold, i - 1);

	t->current_threshold = i - 1;

unlock:

	rcu_read_unlock();

}
@@ -3528,7 +3528,7 @@ static int mem_cgroup_usage_register_event(struct cgroup *cgrp, 
			compare_thresholds, NULL);



	/* Find current threshold */

	atomic_set(&thresholds_new->current_threshold, -1);

	thresholds_new->current_threshold = -1;

	for (i = 0; i < size; i++) {

		if (thresholds_new->entries[i].threshold < usage) {

			/*
@@ -3536,7 +3536,7 @@ static int mem_cgroup_usage_register_event(struct cgroup *cgrp, 
			 * until rcu_assign_pointer(), so it's safe to increment

			 * it here.

			 */

			atomic_inc(&thresholds_new->current_threshold);

			++thresholds_new->current_threshold;

		}

	}
@@ -3607,7 +3607,7 @@ static int mem_cgroup_usage_unregister_event(struct cgroup *cgrp, 
	thresholds_new->size = size;



	/* Copy thresholds and find current threshold */

	atomic_set(&thresholds_new->current_threshold, -1);

	thresholds_new->current_threshold = -1;

	for (i = 0, j = 0; i < thresholds->size; i++) {

		if (thresholds->entries[i].eventfd == eventfd)

			continue;
@@ -3619,7 +3619,7 @@ static int mem_cgroup_usage_unregister_event(struct cgroup *cgrp, 
			 * until rcu_assign_pointer(), so it's safe to increment

			 * it here.

			 */

			atomic_inc(&thresholds_new->current_threshold);

			++thresholds_new->current_threshold;

		}

		j++;

	}