Re: [PATCH 2/2] memcg: share event counter rather than duplicate

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Feb 12, 2010 at 8:48 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> Memcg has 2 eventcountes which counts "the same" event. Just usages are
> different from each other. This patch tries to reduce event counter.
>
> This patch's logic uses "only increment, no reset" new_counter and masks for each
> checks. Softlimit chesk was done per 1000 events. So, the similar check
> can be done by !(new_counter & 0x3ff). Threshold check was done per 100
> events. So, the similar check can be done by (!new_counter & 0x7f)

IIUC, with this change we have to check counter after each update,
since we check
for exact value. So we have to move checks to mem_cgroup_charge_statistics() or
call them after each statistics charging. I'm not sure how it affects
performance.

> Cc: Kirill A. Shutemov <kirill@shutemov.name>
> Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  mm/memcontrol.c |   36 ++++++++++++------------------------
>  1 file changed, 12 insertions(+), 24 deletions(-)
>
> Index: mmotm-2.6.33-Feb10/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.33-Feb10.orig/mm/memcontrol.c
> +++ mmotm-2.6.33-Feb10/mm/memcontrol.c
> @@ -63,8 +63,8 @@ static int really_do_swap_account __init
>  #define do_swap_account                (0)
>  #endif
>
> -#define SOFTLIMIT_EVENTS_THRESH (1000)
> -#define THRESHOLDS_EVENTS_THRESH (100)
> +#define SOFTLIMIT_EVENTS_THRESH (0x3ff) /* once in 1024 */
> +#define THRESHOLDS_EVENTS_THRESH (0x7f) /* once in 128 */
>
>  /*
>  * Statistics for memory cgroup.
> @@ -79,10 +79,7 @@ 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_SWAPOUT, /* # of pages, swapped out */
> -       MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
> -                                       used by soft limit implementation */
> -       MEM_CGROUP_STAT_THRESHOLDS, /* decrements on each page in/out.
> -                                       used by threshold implementation */
> +       MEM_CGROUP_EVENTS,      /* incremented by 1 at pagein/pageout */
>
>        MEM_CGROUP_STAT_NSTATS,
>  };
> @@ -394,16 +391,12 @@ mem_cgroup_remove_exceeded(struct mem_cg
>
>  static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
>  {
> -       bool ret = false;
>        s64 val;
>
> -       val = this_cpu_read(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT]);
> -       if (unlikely(val < 0)) {
> -               this_cpu_write(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT],
> -                               SOFTLIMIT_EVENTS_THRESH);
> -               ret = true;
> -       }
> -       return ret;
> +       val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
> +       if (unlikely(!(val & SOFTLIMIT_EVENTS_THRESH)))
> +               return true;
> +       return false;
>  }
>
>  static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
> @@ -542,8 +535,7 @@ static void mem_cgroup_charge_statistics
>                __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGIN_COUNT]);
>        else
>                __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGOUT_COUNT]);
> -       __this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT]);
> -       __this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS]);
> +       __this_cpu_dec(mem->stat->count[MEM_CGROUP_EVENTS]);
>
>        preempt_enable();
>  }
> @@ -3211,16 +3203,12 @@ static int mem_cgroup_swappiness_write(s
>
>  static bool mem_cgroup_threshold_check(struct mem_cgroup *mem)
>  {
> -       bool ret = false;
>        s64 val;
>
> -       val = this_cpu_read(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS]);
> -       if (unlikely(val < 0)) {
> -               this_cpu_write(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS],
> -                               THRESHOLDS_EVENTS_THRESH);
> -               ret = true;
> -       }
> -       return ret;
> +       val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
> +       if (unlikely(!(val & THRESHOLDS_EVENTS_THRESH)))
> +               return true;
> +       return false;
>  }
>
>  static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
>
>

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