Messages in this thread Patch in this message | | | From | Phil Carmody <> | Subject | [PATCH 1/2] mm: remove unnecessary use of atomic | Date | Wed, 5 May 2010 14:21:48 +0300 |
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From: Phil Carmody <ext-phil.2.carmody@nokia.com>
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> --- mm/memcontrol.c | 14 +++++++------- 1 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6c755de..90e32b2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -151,7 +151,7 @@ struct mem_cgroup_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 */ @@ -3327,7 +3327,7 @@ 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 @@ -3351,7 +3351,7 @@ 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(); } @@ -3429,7 +3429,7 @@ static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft, 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) { /* @@ -3437,7 +3437,7 @@ static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft, * until rcu_assign_pointer(), so it's safe to increment * it here. */ - atomic_inc(&thresholds_new->current_threshold); + ++thresholds_new->current_threshold; } } @@ -3508,7 +3508,7 @@ static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft, 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; @@ -3520,7 +3520,7 @@ static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft, * until rcu_assign_pointer(), so it's safe to increment * it here. */ - atomic_inc(&thresholds_new->current_threshold); + ++thresholds_new->current_threshold; } j++; } -- 1.6.0.4
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