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    SubjectRe: [patch] mm: memcg: shorten preempt-disabled section around event checks
    On Mon, Nov 21, 2011 at 12:09:54PM +0100, Johannes Weiner wrote:
    > -rt ran into a problem with the soft limit spinlock inside the
    > non-preemptible section, because that is sleeping inside an atomic
    > context. But I think it makes sense for vanilla, too, to keep the
    > non-preemptible section as short as possible. Also, -3 lines.
    >
    > Yong, Luis, could you add your Tested-bys?

    Sure, but note that my tests were actually quite limited ;-)

    Tested-by: Luis Henriques <henrix@camandro.org>

    > ---
    > 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@redhat.com>
    > Reported-by: Yong Zhang <yong.zhang0@gmail.com>
    > Reported-by: Luis Henriques <henrix@camandro.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Steven Rostedt <rostedt@goodmis.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > ---
    > mm/memcontrol.c | 73 ++++++++++++++++++++++++++----------------------------
    > 1 files changed, 35 insertions(+), 38 deletions(-)
    >
    > 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)


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