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    Subject[RFC][PATCH 3/8] trigger for updating soft limit information
    From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    Check/Update softlimit information at every charge is over-killing, so
    we need some filter.

    This patch tries to count events in the memcg and if events > threshold
    tries to update memcg's soft limit status and reset event counter to 0.
    Both of page-in/out is counted as event.

    Event counter is maintained by per-cpu which has been already used,
    Then, no siginificant overhead(extra cache-miss etc..) in theory.

    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    ---
    Index: mmotm-2.6.29-Mar23/mm/memcontrol.c
    ===================================================================
    --- mmotm-2.6.29-Mar23.orig/mm/memcontrol.c
    +++ mmotm-2.6.29-Mar23/mm/memcontrol.c
    @@ -66,6 +66,7 @@ enum mem_cgroup_stat_index {
    MEM_CGROUP_STAT_PGPGIN_COUNT, /* # of pages paged in */
    MEM_CGROUP_STAT_PGPGOUT_COUNT, /* # of pages paged out */

    + MEM_CGROUP_STAT_EVENTS, /* sum of page-in/page-out for internal use */
    MEM_CGROUP_STAT_NSTATS,
    };

    @@ -105,6 +106,22 @@ static s64 mem_cgroup_local_usage(struct
    return ret;
    }

    +/* For intenal use of per-cpu event counting. */
    +
    +static inline void
    +__mem_cgroup_stat_reset_safe(struct mem_cgroup_stat_cpu *stat,
    + enum mem_cgroup_stat_index idx)
    +{
    + stat->count[idx] = 0;
    +}
    +
    +static inline s64
    +__mem_cgroup_stat_read_local(struct mem_cgroup_stat_cpu *stat,
    + enum mem_cgroup_stat_index idx)
    +{
    + return stat->count[idx];
    +}
    +
    /*
    * per-zone information in memory controller.
    */
    @@ -235,6 +252,8 @@ static void mem_cgroup_charge_statistics
    else
    __mem_cgroup_stat_add_safe(cpustat,
    MEM_CGROUP_STAT_PGPGOUT_COUNT, 1);
    + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_EVENTS, 1);
    +
    put_cpu();
    }

    @@ -897,9 +916,26 @@ static void record_last_oom(struct mem_c
    mem_cgroup_walk_tree(mem, NULL, record_last_oom_cb);
    }

    +#define SOFTLIMIT_EVENTS_THRESH (1024) /* 1024 times of page-in/out */
    +/*
    + * Returns true if sum of page-in/page-out events since last check is
    + * over SOFTLIMIT_EVENT_THRESH. (counter is per-cpu.)
    + */
    static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
    {
    - return false;
    + bool ret = false;
    + int cpu = get_cpu();
    + s64 val;
    + struct mem_cgroup_stat_cpu *cpustat;
    +
    + cpustat = &mem->stat.cpustat[cpu];
    + val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_EVENTS);
    + if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) {
    + __mem_cgroup_stat_reset_safe(cpustat, MEM_CGROUP_STAT_EVENTS);
    + ret = true;
    + }
    + put_cpu();
    + return ret;
    }

    static void mem_cgroup_update_soft_limit(struct mem_cgroup *mem)


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