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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: Phil Carmody <ext-phil.2.carmody@nokia.com>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Phil Carmody 2010-05-26 14:42:42 -07:00 committed by Linus Torvalds
parent df64f81bb1
commit 5407a56257
1 changed files with 7 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
mm/memcontrol.c
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@ -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++;
}