Re: [RFC][PATCH 3/5] memcg: Disable preemption in memcg_check_events()

Johannes Weiner
2011-09-20T14:25:05Z

On Tue, Sep 20, 2011 at 04:20:31PM +0200, Johannes Weiner wrote:
> On Mon, Sep 19, 2011 at 05:20:43PM -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <srostedt@redhat.com>
> >
> > The code in memcg_check_events() calls this_cpu_read() on
> > different variables without disabling preemption, and can cause
> > the calculations to be done from two different CPU variables.
> >
> > Disable preemption throughout the check to keep apples and oranges
> > from becoming a mixed drink.
>
> Makes sense, thanks!
>
> Since the atomic versions are no longer required with preemption
> disabled explicitely, could you also make the this_cpu ops in
> __memcg_event_check and __mem_cgroup_target_update non-atomic in the
> same go?

Sorry, shouldn't be on you, can you fold this in?

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b76011a..9d4ba65 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -683,8 +683,8 @@ static bool __memcg_event_check(struct mem_cgroup *memcg, int target)
{
unsigned long val, next;

- val = this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
- next = this_cpu_read(memcg->stat->targets[target]);
+ 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);
}
@@ -693,7 +693,7 @@ 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]);
+ val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);

switch (target) {
case MEM_CGROUP_TARGET_THRESH:
@@ -709,7 +709,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target)
return;
}

- this_cpu_write(memcg->stat->targets[target], next);
+ __this_cpu_write(memcg->stat->targets[target], next);
}

/*