Re: [PATCH -rt] memcg: use migrate_disable()/migrate_enable( ) in memcg_check_events()
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2011-11-16 14:12:43
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On Wed, 2011-11-16 at 17:16 +0800, Yong Zhang wrote:
Looking at commit 4799401f [memcg: Fix race condition in memcg_check_events() with this_cpu usage], we just want to disable migration. So use the right API in -rt. This will cure below warning.
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mm/memcontrol.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6aff93c..afa1954 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -722,7 +722,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target) */ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page) { - preempt_disable(); + migrate_disable();
No this won't work. Not even for -rt. If we disable migration but not preemption, then two tasks can take this path. And the checks in __memcg_event_check() will be corrupted because nothing is protecting the updates from two tasks going into the same path. Perhaps a local_lock would work. -- Steve
quoted hunk ↗ jump to hunk
/* threshold event is triggered in finer grain than soft limit */ if (unlikely(__memcg_event_check(memcg, MEM_CGROUP_TARGET_THRESH))) { mem_cgroup_threshold(memcg);@@ -742,7 +742,7 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page) } #endif } - preempt_enable(); + migrate_enable(); } static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)