Re: [PATCH 4/7] memcg fix scan ratio with small memcg.

[Ying Han <yinghan@google.com>]

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On Mon, Apr 25, 2011 at 2:34 AM, KAMEZAWA Hiroyuki <
kamezawa.hiroyu@jp.fujitsu.com> wrote:

>
> At memcg memory reclaim, get_scan_count() may returns [0, 0, 0, 0]
> and no scan was not issued at the reclaim priority.
>
> The reason is because memory cgroup may not be enough big to have
> the number of pages, which is greater than 1 << priority.
>
> Because priority affects many routines in vmscan.c, it's better
> to scan memory even if usage >> priority < 0.
> From another point of view, if memcg's zone doesn't have enough memory
> which
> meets priority, it should be skipped. So, this patch creates a temporal
> priority
> in get_scan_count() and scan some amount of pages even when
> usage is small. By this, memcg's reclaim goes smoother without
> having too high priority, which will cause unnecessary congestion_wait(),
> etc.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  include/linux/memcontrol.h |    6 ++++++
>  mm/memcontrol.c            |    5 +++++
>  mm/vmscan.c                |   11 +++++++++++
>  3 files changed, 22 insertions(+)
>
> Index: memcg/include/linux/memcontrol.h
> ===================================================================
> --- memcg.orig/include/linux/memcontrol.h
> +++ memcg/include/linux/memcontrol.h
> @@ -152,6 +152,7 @@ unsigned long mem_cgroup_soft_limit_recl
>                                                gfp_t gfp_mask,
>                                                unsigned long
> *total_scanned);
>  u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
> +u64 mem_cgroup_get_usage(struct mem_cgroup *mem);
>
>  void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item
> idx);
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> @@ -357,6 +358,11 @@ u64 mem_cgroup_get_limit(struct mem_cgro
>        return 0;
>  }
>
> +static inline u64 mem_cgroup_get_limit(struct mem_cgroup *mem)
> +{
> +       return 0;
> +}
> +
>

should be  mem_cgroup_get_usage()


 static inline void mem_cgroup_split_huge_fixup(struct page *head,
>                                                struct page *tail)
>  {
> Index: memcg/mm/memcontrol.c
> ===================================================================
> --- memcg.orig/mm/memcontrol.c
> +++ memcg/mm/memcontrol.c
> @@ -1483,6 +1483,11 @@ u64 mem_cgroup_get_limit(struct mem_cgro
>        return min(limit, memsw);
>  }
>
> +u64 mem_cgroup_get_usage(struct mem_cgroup *memcg)
> +{
> +       return res_counter_read_u64(&memcg->res, RES_USAGE);
> +}
> +
>  /*
>  * Visit the first child (need not be the first child as per the ordering
>  * of the cgroup list, since we track last_scanned_child) of @mem and use
> Index: memcg/mm/vmscan.c
> ===================================================================
> --- memcg.orig/mm/vmscan.c
> +++ memcg/mm/vmscan.c
> @@ -1762,6 +1762,17 @@ static void get_scan_count(struct zone *
>                        denominator = 1;
>                        goto out;
>                }
> +       } else {
> +               u64 usage;
> +               /*
> +                * When memcg is enough small, anon+file >> priority
> +                * can be 0 and we'll do no scan. Adjust it to proper
> +                * value against its usage. If this zone's usage is enough
> +                * small, scan will ignore this zone until priority goes
> down.
> +                */
> +               for (usage = mem_cgroup_get_usage(sc->mem_cgroup) >>
> PAGE_SHIFT;
> +                    priority && ((usage >> priority) < SWAP_CLUSTER_MAX);
> +                    priority--);
>        }
>

--Ying

>
>        /*
>
>

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