On Thu, 17 Nov 2011, Yong Zhang wrote:
> On Wed, Nov 16, 2011 at 06:02:42PM +0100, Thomas Gleixner wrote:
> > On Wed, 16 Nov 2011, Steven Rostedt wrote:
> > > 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.
> > > 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.
> >
> > Yes, that's the only sensible option for now. Untested patch below.
>
> Works for me.
Johannes came up with a different solution. Could you please give it a try?
Thanks,
tglx
------------->
Subject: [patch] mm: memcg: shorten preempt-disabled section around event checks
Only the ratelimit checks themselves have to run with preemption
disabled, the resulting actions - checking for usage thresholds,
updating the soft limit tree - can and should run with preemption
enabled.
Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx>
---
mm/memcontrol.c | 73 ++++++++++++++++++++++++++----------------------------
1 files changed, 35 insertions(+), 38 deletions(-)
Thomas, HTH and it is probably interesting for upstream as well.
Unfortunately, I'm in the middle of moving right now, so this is
untested except for compiling.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6aff93c..8e62d3e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -683,37 +683,32 @@ static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
return total;
}
-static bool __memcg_event_check(struct mem_cgroup *memcg, int target)
+static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
+ enum mem_cgroup_events_target target)
{
unsigned long val, next;
val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
next = __this_cpu_read(memcg->stat->targets[target]);
/* from time_after() in jiffies.h */
- return ((long)next - (long)val < 0);
-}
-
-static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target)
-{
- unsigned long val, next;
-
- val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
-
- switch (target) {
- case MEM_CGROUP_TARGET_THRESH:
- next = val + THRESHOLDS_EVENTS_TARGET;
- break;
- case MEM_CGROUP_TARGET_SOFTLIMIT:
- next = val + SOFTLIMIT_EVENTS_TARGET;
- break;
- case MEM_CGROUP_TARGET_NUMAINFO:
- next = val + NUMAINFO_EVENTS_TARGET;
- break;
- default:
- return;
+ if ((long)next - (long)val < 0) {
+ switch (target) {
+ case MEM_CGROUP_TARGET_THRESH:
+ next = val + THRESHOLDS_EVENTS_TARGET;
+ break;
+ case MEM_CGROUP_TARGET_SOFTLIMIT:
+ next = val + SOFTLIMIT_EVENTS_TARGET;
+ break;
+ case MEM_CGROUP_TARGET_NUMAINFO:
+ next = val + NUMAINFO_EVENTS_TARGET;
+ break;
+ default:
+ break;
+ }
+ __this_cpu_write(memcg->stat->targets[target], next);
+ return true;
}
-
- __this_cpu_write(memcg->stat->targets[target], next);
+ return false;
}
/*
@@ -724,25 +719,27 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
{
preempt_disable();
/* threshold event is triggered in finer grain than soft limit */
- if (unlikely(__memcg_event_check(memcg, MEM_CGROUP_TARGET_THRESH))) {
+ if (unlikely(mem_cgroup_event_ratelimit(memcg,
+ MEM_CGROUP_TARGET_THRESH))) {
+ bool do_softlimit, do_numainfo;
+
+ do_softlimit = mem_cgroup_event_ratelimit(memcg,
+ MEM_CGROUP_TARGET_SOFTLIMIT);
+#if MAX_NUMNODES > 1
+ do_numainfo = mem_cgroup_event_ratelimit(memcg,
+ MEM_CGROUP_TARGET_NUMAINFO);
+#endif
+ preempt_enable();
+
mem_cgroup_threshold(memcg);
- __mem_cgroup_target_update(memcg, MEM_CGROUP_TARGET_THRESH);
- if (unlikely(__memcg_event_check(memcg,
- MEM_CGROUP_TARGET_SOFTLIMIT))) {
+ if (unlikely(do_softlimit))
mem_cgroup_update_tree(memcg, page);
- __mem_cgroup_target_update(memcg,
- MEM_CGROUP_TARGET_SOFTLIMIT);
- }
#if MAX_NUMNODES > 1
- if (unlikely(__memcg_event_check(memcg,
- MEM_CGROUP_TARGET_NUMAINFO))) {
+ if (unlikely(do_numainfo))
atomic_inc(&memcg->numainfo_events);
- __mem_cgroup_target_update(memcg,
- MEM_CGROUP_TARGET_NUMAINFO);
- }
#endif
- }
- preempt_enable();
+ } else
+ preempt_enable();
}
static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
--
1.7.6.4
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