Re: [PATCH V4 07/10] Add per-memcg zone "unreclaimable"

[Zhu Yanhai <zhu.yanhai@gmail.com>]

2011/4/15 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>:
> On Thu, 14 Apr 2011 15:54:26 -0700
> Ying Han <yinghan@google.com> wrote:
>
>> After reclaiming each node per memcg, it checks mem_cgroup_watermark_ok()
>> and breaks the priority loop if it returns true. The per-memcg zone will
>> be marked as "unreclaimable" if the scanning rate is much greater than the
>> reclaiming rate on the per-memcg LRU. The bit is cleared when there is a
>> page charged to the memcg being freed. Kswapd breaks the priority loop if
>> all the zones are marked as "unreclaimable".
>>
>> changelog v4..v3:
>> 1. split off from the per-memcg background reclaim patch in V3.
>>
>> Signed-off-by: Ying Han <yinghan@google.com>
>> ---
>>  include/linux/memcontrol.h |   30 ++++++++++++++
>>  include/linux/swap.h       |    2 +
>>  mm/memcontrol.c            |   96 ++++++++++++++++++++++++++++++++++++++++++++
>>  mm/vmscan.c                |   19 +++++++++
>>  4 files changed, 147 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index d4ff7f2..a8159f5 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -155,6 +155,12 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>>                                               gfp_t gfp_mask);
>>  u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
>> +void mem_cgroup_clear_unreclaimable(struct mem_cgroup *mem, struct page *page);
>> +bool mem_cgroup_zone_reclaimable(struct mem_cgroup *mem, int nid, int zid);
>> +bool mem_cgroup_mz_unreclaimable(struct mem_cgroup *mem, struct zone *zone);
>> +void mem_cgroup_mz_set_unreclaimable(struct mem_cgroup *mem, struct zone *zone);
>> +void mem_cgroup_mz_pages_scanned(struct mem_cgroup *mem, struct zone* zone,
>> +                             unsigned long nr_scanned);
>>
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>  void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail);
>> @@ -345,6 +351,25 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>>  {
>>  }
>>
>> +static inline void mem_cgroup_mz_pages_scanned(struct mem_cgroup *mem,
>> +                                             struct zone *zone,
>> +                                             unsigned long nr_scanned)
>> +{
>> +}
>> +
>> +static inline void mem_cgroup_clear_unreclaimable(struct page *page,
>> +                                                     struct zone *zone)
>> +{
>> +}
>> +static inline void mem_cgroup_mz_set_unreclaimable(struct mem_cgroup *mem,
>> +             struct zone *zone)
>> +{
>> +}
>> +static inline bool mem_cgroup_mz_unreclaimable(struct mem_cgroup *mem,
>> +                                             struct zone *zone)
>> +{
>> +}
>> +
>>  static inline
>>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>>                                           gfp_t gfp_mask)
>> @@ -363,6 +388,11 @@ static inline void mem_cgroup_split_huge_fixup(struct page *head,
>>  {
>>  }
>>
>> +static inline bool mem_cgroup_zone_reclaimable(struct mem_cgroup *mem, int nid,
>> +                                                             int zid)
>> +{
>> +     return false;
>> +}
>>  #endif /* CONFIG_CGROUP_MEM_CONT */
>>
>>  #if !defined(CONFIG_CGROUP_MEM_RES_CTLR) || !defined(CONFIG_DEBUG_VM)
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index 17e0511..319b800 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -160,6 +160,8 @@ enum {
>>       SWP_SCANNING    = (1 << 8),     /* refcount in scan_swap_map */
>>  };
>>
>> +#define ZONE_RECLAIMABLE_RATE 6
>> +
>>  #define SWAP_CLUSTER_MAX 32
>>  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index e22351a..da6a130 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -133,7 +133,10 @@ struct mem_cgroup_per_zone {
>>       bool                    on_tree;
>>       struct mem_cgroup       *mem;           /* Back pointer, we cannot */
>>                                               /* use container_of        */
>> +     unsigned long           pages_scanned;  /* since last reclaim */
>> +     bool                    all_unreclaimable;      /* All pages pinned */
>>  };
>> +
>>  /* Macro for accessing counter */
>>  #define MEM_CGROUP_ZSTAT(mz, idx)    ((mz)->count[(idx)])
>>
>> @@ -1135,6 +1138,96 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
>>       return &mz->reclaim_stat;
>>  }
>>
>> +static unsigned long mem_cgroup_zone_reclaimable_pages(
>> +                                     struct mem_cgroup_per_zone *mz)
>> +{
>> +     int nr;
>> +     nr = MEM_CGROUP_ZSTAT(mz, LRU_ACTIVE_FILE) +
>> +             MEM_CGROUP_ZSTAT(mz, LRU_INACTIVE_FILE);
>> +
>> +     if (nr_swap_pages > 0)
>> +             nr += MEM_CGROUP_ZSTAT(mz, LRU_ACTIVE_ANON) +
>> +                     MEM_CGROUP_ZSTAT(mz, LRU_INACTIVE_ANON);
>> +
>> +     return nr;
>> +}
>> +
>> +void mem_cgroup_mz_pages_scanned(struct mem_cgroup *mem, struct zone* zone,
>> +                                             unsigned long nr_scanned)
>> +{
>> +     struct mem_cgroup_per_zone *mz = NULL;
>> +     int nid = zone_to_nid(zone);
>> +     int zid = zone_idx(zone);
>> +
>> +     if (!mem)
>> +             return;
>> +
>> +     mz = mem_cgroup_zoneinfo(mem, nid, zid);
>> +     if (mz)
>> +             mz->pages_scanned += nr_scanned;
>> +}
>> +
>> +bool mem_cgroup_zone_reclaimable(struct mem_cgroup *mem, int nid, int zid)
>> +{
>> +     struct mem_cgroup_per_zone *mz = NULL;
>> +
>> +     if (!mem)
>> +             return 0;
>> +
>> +     mz = mem_cgroup_zoneinfo(mem, nid, zid);
>> +     if (mz)
>> +             return mz->pages_scanned <
>> +                             mem_cgroup_zone_reclaimable_pages(mz) *
>> +                             ZONE_RECLAIMABLE_RATE;
>> +     return 0;
>> +}
>> +
>> +bool mem_cgroup_mz_unreclaimable(struct mem_cgroup *mem, struct zone *zone)
>> +{
>> +     struct mem_cgroup_per_zone *mz = NULL;
>> +     int nid = zone_to_nid(zone);
>> +     int zid = zone_idx(zone);
>> +
>> +     if (!mem)
>> +             return false;
>> +
>> +     mz = mem_cgroup_zoneinfo(mem, nid, zid);
>> +     if (mz)
>> +             return mz->all_unreclaimable;
>> +
>> +     return false;
>> +}
>> +
>> +void mem_cgroup_mz_set_unreclaimable(struct mem_cgroup *mem, struct zone *zone)
>> +{
>> +     struct mem_cgroup_per_zone *mz = NULL;
>> +     int nid = zone_to_nid(zone);
>> +     int zid = zone_idx(zone);
>> +
>> +     if (!mem)
>> +             return;
>> +
>> +     mz = mem_cgroup_zoneinfo(mem, nid, zid);
>> +     if (mz)
>> +             mz->all_unreclaimable = true;
>> +}
>> +
>> +void mem_cgroup_clear_unreclaimable(struct mem_cgroup *mem, struct page *page)
>> +{
>> +     struct mem_cgroup_per_zone *mz = NULL;
>> +
>> +     if (!mem)
>> +             return;
>> +
>> +     mz = page_cgroup_zoneinfo(mem, page);
>> +     if (mz) {
>> +             mz->pages_scanned = 0;
>> +             mz->all_unreclaimable = false;
>> +     }
>> +
>> +     return;
>> +}
>> +
>>  unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>>                                       struct list_head *dst,
>>                                       unsigned long *scanned, int order,
>> @@ -2801,6 +2894,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
>>        * special functions.
>>        */
>>
>> +     mem_cgroup_clear_unreclaimable(mem, page);
>
> Hmm, this will easily cause cache ping-pong. (free_page() clears it after taking
> zone->lock....in batched manner.)
>
> Could you consider a way to make this low cost ?
>
> One way is using memcg_check_event() with some low event trigger.
> Second way is usign memcg_batch.
> In many case, we can expect a chunk of free pages are from the same zone.
> Then, add a new member to batch_memcg as
>
> struct memcg_batch_info {
>        .....
>        struct zone *zone;      # a zone page is last uncharged.
>        ...
> }
>
> Then,
> ==
> static void mem_cgroup_do_uncharge(struct mem_cgroup *mem,
>                                   unsigned int nr_pages,
> +                                  struct page *page,
>                                   const enum charge_type ctype)
> {
>        struct memcg_batch_info *batch = NULL;
> .....
>
>        if (batch->zone != page_zone(page)) {
>                mem_cgroup_clear_unreclaimable(mem, page);
>        }
> direct_uncharge:
>        mem_cgroup_clear_unreclaimable(mem, page);
> ....
> }
> ==
>
> This will reduce overhead dramatically.
>

Excuse me but I don't quite understand this part, IMHO this is to
avoid call mem_cgroup_clear_unreclaimable() against each single page
during a munmap()/free_pages() including many pages to free, which is
unnecessary because the zone will turn into 'reclaimable' at the first
page uncharged.
Then why can't we just say,
   if (mem_cgroup_zoneinfo(mem, page_to_nid(page),
page_zonenum(page))->all_unreclaimable) {
            mem_cgroup_clear_unreclaimable(mem, page);
    }

--
Thanks,
Zhu Yanhai


>
>
>>       unlock_page_cgroup(pc);
>>       /*
>>        * even after unlock, we have mem->res.usage here and this memcg
>> @@ -4569,6 +4663,8 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
>>               mz->usage_in_excess = 0;
>>               mz->on_tree = false;
>>               mz->mem = mem;
>> +             mz->pages_scanned = 0;
>> +             mz->all_unreclaimable = false;
>>       }
>>       return 0;
>>  }
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index b8345d2..c081112 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1414,6 +1414,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
>>                                       ISOLATE_BOTH : ISOLATE_INACTIVE,
>>                       zone, sc->mem_cgroup,
>>                       0, file);
>> +
>> +             mem_cgroup_mz_pages_scanned(sc->mem_cgroup, zone, nr_scanned);
>> +
>>               /*
>>                * mem_cgroup_isolate_pages() keeps track of
>>                * scanned pages on its own.
>> @@ -1533,6 +1536,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
>>                * mem_cgroup_isolate_pages() keeps track of
>>                * scanned pages on its own.
>>                */
>> +             mem_cgroup_mz_pages_scanned(sc->mem_cgroup, zone, pgscanned);
>>       }
>>
>>       reclaim_stat->recent_scanned[file] += nr_taken;
>> @@ -2648,6 +2652,7 @@ static void balance_pgdat_node(pg_data_t *pgdat, int order,
>>       unsigned long total_scanned = 0;
>>       struct mem_cgroup *mem_cont = sc->mem_cgroup;
>>       int priority = sc->priority;
>> +     int nid = pgdat->node_id;
>>
>>       /*
>>        * Now scan the zone in the dma->highmem direction, and we scan
>> @@ -2664,10 +2669,20 @@ static void balance_pgdat_node(pg_data_t *pgdat, int order,
>>               if (!populated_zone(zone))
>>                       continue;
>>
>> +             if (mem_cgroup_mz_unreclaimable(mem_cont, zone) &&
>> +                     priority != DEF_PRIORITY)
>> +                     continue;
>> +
>>               sc->nr_scanned = 0;
>>               shrink_zone(priority, zone, sc);
>>               total_scanned += sc->nr_scanned;
>>
>> +             if (mem_cgroup_mz_unreclaimable(mem_cont, zone))
>> +                     continue;
>> +
>> +             if (!mem_cgroup_zone_reclaimable(mem_cont, nid, i))
>> +                     mem_cgroup_mz_set_unreclaimable(mem_cont, zone);
>> +
>>               /*
>>                * If we've done a decent amount of scanning and
>>                * the reclaim ratio is low, start doing writepage
>> @@ -2752,6 +2767,10 @@ loop_again:
>>
>>                               if (!populated_zone(zone))
>>                                       continue;
>> +
>> +                             if (!mem_cgroup_mz_unreclaimable(mem_cont,
>> +                                                             zone))
>> +
>
> Ah, okay. this will work.
>
> Thanks,
> -Kame
>

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