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

[Ying Han <yinghan@google.com>]

On Mon, Mar 19, 2012 at 1:27 AM, Zhu Yanhai <zhu.yanhai@gmail.com> wrote:
> 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);
>    }

Are you suggesting to replace the batching w/ the code above?

--Ying
> --
> 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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