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    SubjectRe: [PATCH 3/7] memcg: add memory.scan_stat
    From
    On Wed, Jun 15, 2011 at 8:53 PM, KAMEZAWA Hiroyuki
    <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > From e08990dd9ada13cf236bec1ef44b207436434b8e Mon Sep 17 00:00:00 2001
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Date: Wed, 15 Jun 2011 14:11:01 +0900
    > Subject: [PATCH 3/7] memcg: add memory.scan_stat
    >
    > commit log of commit 0ae5e89 " memcg: count the soft_limit reclaim in..."
    > says it adds scanning stats to memory.stat file. But it doesn't because
    > we considered we needed to make a concensus for such new APIs.
    >
    > This patch is a trial to add memory.scan_stat. This shows
    >  - the number of scanned pages
    >  - the number of recleimed pages
    >  - the number of elaplsed time (including sleep/pause time)
    >  for both of direct/soft reclaim and shrinking caused by changing limit
    >  or force_empty.
    >
    > The biggest difference with oringinal Ying's one is that this file
    > can be reset by some write, as
    >
    >  # echo 0 ...../memory.scan_stat
    >
    > [kamezawa@bluextal ~]$ cat /cgroup/memory/A/memory.scan_stat
    > scanned_pages_by_limit 358470
    > freed_pages_by_limit 180795
    > elapsed_ns_by_limit 21629927
    > scanned_pages_by_system 0
    > freed_pages_by_system 0
    > elapsed_ns_by_system 0
    > scanned_pages_by_shrink 76646
    > freed_pages_by_shrink 38355
    > elappsed_ns_by_shrink 31990670
    > total_scanned_pages_by_limit 358470
    > total_freed_pages_by_limit 180795
    > total_elapsed_ns_by_hierarchical 216299275
    > total_scanned_pages_by_system 0
    > total_freed_pages_by_system 0
    > total_elapsed_ns_by_system 0
    > total_scanned_pages_by_shrink 76646
    > total_freed_pages_by_shrink 38355
    > total_elapsed_ns_by_shrink 31990670
    >
    > total_xxxx is for hierarchy management.
    >
    > This will be useful for further memcg developments and need to be
    > developped before we do some complicated rework on LRU/softlimit
    > management.

    Agreed. Actually we are also looking into adding a per-memcg API for
    adding visibility of
    page reclaim path. It would be helpful for us to settle w/ the API first.

    I am not a fan of names, but how about
    "/dev/cgroup/memory/memory.reclaim_stat" ?

    >
    > Now, scan/free/elapsed_by_system is incomplete but future works of
    > Johannes at el. will fill remaining information and then, we can
    > look into problems of isolation between memcgs.
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    >  Documentation/cgroups/memory.txt |   33 +++++++++
    >  include/linux/memcontrol.h       |   16 ++++
    >  include/linux/swap.h             |    6 -
    >  mm/memcontrol.c                  |  135 +++++++++++++++++++++++++++++++++++++--
    >  mm/vmscan.c                      |   27 ++++++-
    >  5 files changed, 199 insertions(+), 18 deletions(-)
    >
    > Index: mmotm-0615/Documentation/cgroups/memory.txt
    > ===================================================================
    > --- mmotm-0615.orig/Documentation/cgroups/memory.txt
    > +++ mmotm-0615/Documentation/cgroups/memory.txt
    > @@ -380,7 +380,7 @@ will be charged as a new owner of it.
    >
    >  5.2 stat file
    >
    > -memory.stat file includes following statistics
    > +5.2.1 memory.stat file includes following statistics
    >
    >  # per-memory cgroup local status
    >  cache          - # of bytes of page cache memory.
    > @@ -438,6 +438,37 @@ Note:
    >         file_mapped is accounted only when the memory cgroup is owner of page
    >         cache.)
    >
    > +5.2.2 memory.scan_stat
    > +
    > +memory.scan_stat includes statistics information for memory scanning and
    > +freeing, reclaiming. The statistics shows memory scanning information since
    > +memory cgroup creation and can be reset to 0 by writing 0 as
    > +
    > + #echo 0 > ../memory.scan_stat
    > +
    > +This file contains following statistics.
    > +
    > +scanned_pages_by_limit - # of scanned pages at hitting limit.
    > +freed_pages_by_limit   - # of freed pages at hitting limit.

    How those stats different from Johannes's patch? I feel we should keep
    them into this API instead of memory.stat
    "pgscan_direct_limit"
    "pgreclaim_direct_limit"

    > +elapsed_ns_by_limit    - nano sec of elappsed time at LRU scan at
    > +                                  hitting limit.(this includes sleep time.)


    > +
    > +scanned_pages_by_system        - # of scanned pages by the kernel.
    > +                         (Now, this value means global memory reclaim
    > +                           caused by system memory shortage with a hint
    > +                          of softlimit. "No soft limit" case will be
    > +                          supported in future.)
    > +freed_pages_by_system  - # of freed pages by the kernel.

    The same for the following which I assume the same meaning with:
    "pgscan_direct_hierarchy"
    "pgreclaim_direct_hierarchy"

    > +elapsed_ns_by_system   - nano sec of elappsed time by kernel.
    > +
    > +scanned_pages_by_shrink        - # of scanned pages by shrinking.
    > +                                 (i.e. changes of limit, force_empty, etc.)
    > +freed_pages_by_shrink  - # of freed pages by shirkining.

    So those stats are not included in the ones above?

    --Ying

    > +elappsed_ns_by_shrink  - nano sec of elappsed time at shrinking.
    > +
    > +total_xxx includes the statistics of children scanning caused by the cgroup.
    > +
    > +
    >  5.3 swappiness
    >
    >  Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
    > Index: mmotm-0615/include/linux/memcontrol.h
    > ===================================================================
    > --- mmotm-0615.orig/include/linux/memcontrol.h
    > +++ mmotm-0615/include/linux/memcontrol.h
    > @@ -120,6 +120,22 @@ struct zone_reclaim_stat*
    >  mem_cgroup_get_reclaim_stat_from_page(struct page *page);
    >  extern void mem_cgroup_print_oom_info(struct mem_cgroup *memcg,
    >                                        struct task_struct *p);
    > +struct memcg_scanrecord {
    > +       struct mem_cgroup *mem; /* scanend memory cgroup */
    > +       struct mem_cgroup *root; /* scan target hierarchy root */
    > +       int context;            /* scanning context (see memcontrol.c) */
    > +       unsigned long nr_scanned; /* the number of scanned pages */
    > +       unsigned long nr_freed; /* the number of freed pages */
    > +       unsigned long elappsed; /* nsec of time elapsed while scanning */
    > +};
    > +
    > +extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
    > +                                                 gfp_t gfp_mask, bool noswap,
    > +                                                 struct memcg_scanrecord *rec);
    > +extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
    > +                                               gfp_t gfp_mask, bool noswap,
    > +                                               struct zone *zone,
    > +                                               struct memcg_scanrecord *rec);
    >
    >  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
    >  extern int do_swap_account;
    > Index: mmotm-0615/include/linux/swap.h
    > ===================================================================
    > --- mmotm-0615.orig/include/linux/swap.h
    > +++ mmotm-0615/include/linux/swap.h
    > @@ -253,12 +253,6 @@ static inline void lru_cache_add_file(st
    >  /* linux/mm/vmscan.c */
    >  extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
    >                                        gfp_t gfp_mask, nodemask_t *mask);
    > -extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
    > -                                                 gfp_t gfp_mask, bool noswap);
    > -extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
    > -                                               gfp_t gfp_mask, bool noswap,
    > -                                               struct zone *zone,
    > -                                               unsigned long *nr_scanned);
    >  extern int __isolate_lru_page(struct page *page, int mode, int file);
    >  extern unsigned long shrink_all_memory(unsigned long nr_pages);
    >  extern int vm_swappiness;
    > Index: mmotm-0615/mm/memcontrol.c
    > ===================================================================
    > --- mmotm-0615.orig/mm/memcontrol.c
    > +++ mmotm-0615/mm/memcontrol.c
    > @@ -203,6 +203,57 @@ struct mem_cgroup_eventfd_list {
    >  static void mem_cgroup_threshold(struct mem_cgroup *mem);
    >  static void mem_cgroup_oom_notify(struct mem_cgroup *mem);
    >
    > +enum {
    > +       SCAN_BY_LIMIT,
    > +       FREED_BY_LIMIT,
    > +       ELAPSED_BY_LIMIT,
    > +
    > +       SCAN_BY_SYSTEM,
    > +       FREED_BY_SYSTEM,
    > +       ELAPSED_BY_SYSTEM,
    > +
    > +       SCAN_BY_SHRINK,
    > +       FREED_BY_SHRINK,
    > +       ELAPSED_BY_SHRINK,
    > +       NR_SCANSTATS,
    > +};
    > +#define __FREED                (1)
    > +#define        __ELAPSED       (2)
    > +
    > +struct scanstat {
    > +       spinlock_t      lock;
    > +       unsigned long   stats[NR_SCANSTATS];    /* local statistics */
    > +       unsigned long   totalstats[NR_SCANSTATS];   /* hierarchical */
    > +};
    > +
    > +const char *scanstat_string[NR_SCANSTATS] = {
    > +       "scanned_pages_by_limit",
    > +       "freed_pages_by_limit",
    > +       "elapsed_ns_by_limit",
    > +
    > +       "scanned_pages_by_system",
    > +       "freed_pages_by_system",
    > +       "elapsed_ns_by_system",
    > +
    > +       "scanned_pages_by_shrink",
    > +       "freed_pages_by_shrink",
    > +       "elappsed_ns_by_shrink",
    > +};
    > +
    > +const char *total_scanstat_string[NR_SCANSTATS] = {
    > +       "total_scanned_pages_by_limit",
    > +       "total_freed_pages_by_limit",
    > +       "total_elapsed_ns_by_hierarchical",
    > +
    > +       "total_scanned_pages_by_system",
    > +       "total_freed_pages_by_system",
    > +       "total_elapsed_ns_by_system",
    > +
    > +       "total_scanned_pages_by_shrink",
    > +       "total_freed_pages_by_shrink",
    > +       "total_elapsed_ns_by_shrink",
    > +};
    > +
    >  /*
    >  * The memory controller data structure. The memory controller controls both
    >  * page cache and RSS per cgroup. We would eventually like to provide
    > @@ -264,7 +315,8 @@ struct mem_cgroup {
    >
    >        /* For oom notifier event fd */
    >        struct list_head oom_notify;
    > -
    > +       /* For recording LRU-scan statistics */
    > +       struct scanstat scanstat;
    >        /*
    >         * Should we move charges of a task when a task is moved into this
    >         * mem_cgroup ? And what type of charges should we move ?
    > @@ -1634,6 +1686,28 @@ int mem_cgroup_select_victim_node(struct
    >  }
    >  #endif
    >
    > +
    > +
    > +static void mem_cgroup_record_scanstat(struct memcg_scanrecord *rec)
    > +{
    > +       struct mem_cgroup *mem;
    > +       int context = rec->context;
    > +
    > +       mem = rec->mem;
    > +       spin_lock(&mem->scanstat.lock);
    > +       mem->scanstat.stats[context] += rec->nr_scanned;
    > +       mem->scanstat.stats[context + __FREED] += rec->nr_freed;
    > +       mem->scanstat.stats[context + __ELAPSED] += rec->elappsed;
    > +       spin_unlock(&mem->scanstat.lock);
    > +
    > +       mem = rec->root;
    > +       spin_lock(&mem->scanstat.lock);
    > +       mem->scanstat.totalstats[context] += rec->nr_scanned;
    > +       mem->scanstat.totalstats[context + __FREED] += rec->nr_freed;
    > +       mem->scanstat.totalstats[context + __ELAPSED] += rec->elappsed;
    > +       spin_unlock(&mem->scanstat.lock);
    > +}
    > +
    >  /*
    >  * Scan the hierarchy if needed to reclaim memory. We remember the last child
    >  * we reclaimed from, so that we don't end up penalizing one child extensively
    > @@ -1659,8 +1733,8 @@ static int mem_cgroup_hierarchical_recla
    >        bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
    >        bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
    >        unsigned long excess;
    > -       unsigned long nr_scanned;
    >        int visit;
    > +       struct memcg_scanrecord rec;
    >
    >        excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
    >
    > @@ -1668,6 +1742,15 @@ static int mem_cgroup_hierarchical_recla
    >        if (!check_soft && root_mem->memsw_is_minimum)
    >                noswap = true;
    >
    > +       if (shrink)
    > +               rec.context = SCAN_BY_SHRINK;
    > +       else if (check_soft)
    > +               rec.context = SCAN_BY_SYSTEM;
    > +       else
    > +               rec.context = SCAN_BY_LIMIT;
    > +
    > +       rec.root = root_mem;
    > +
    >  again:
    >        if (!shrink) {
    >                visit = 0;
    > @@ -1695,14 +1778,19 @@ again:
    >                        css_put(&victim->css);
    >                        continue;
    >                }
    > +               rec.mem = victim;
    > +               rec.nr_scanned = 0;
    > +               rec.nr_freed = 0;
    > +               rec.elappsed = 0;
    >                /* we use swappiness of local cgroup */
    >                if (check_soft) {
    >                        ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,
    > -                               noswap, zone, &nr_scanned);
    > -                       *total_scanned += nr_scanned;
    > +                               noswap, zone, &rec);
    > +                       *total_scanned += rec.nr_scanned;
    >                } else
    >                        ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
    > -                                               noswap);
    > +                                               noswap, &rec);
    > +               mem_cgroup_record_scanstat(&rec);
    >                css_put(&victim->css);
    >
    >                total += ret;
    > @@ -3757,7 +3845,8 @@ try_to_free:
    >                        ret = -EINTR;
    >                        goto out;
    >                }
    > -               progress = try_to_free_mem_cgroup_pages(mem, GFP_KERNEL, false);
    > +               progress = try_to_free_mem_cgroup_pages(mem,
    > +                               GFP_KERNEL, false, NULL);
    >                if (!progress) {
    >                        nr_retries--;
    >                        /* maybe some writeback is necessary */
    > @@ -4599,6 +4688,34 @@ static int mem_control_numa_stat_open(st
    >  }
    >  #endif /* CONFIG_NUMA */
    >
    > +static int mem_cgroup_scan_stat_read(struct cgroup *cgrp,
    > +                               struct cftype *cft,
    > +                               struct cgroup_map_cb *cb)
    > +{
    > +       struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
    > +       int i;
    > +
    > +       for (i = 0; i < NR_SCANSTATS; i++)
    > +               cb->fill(cb, scanstat_string[i], mem->scanstat.stats[i]);
    > +       for (i = 0; i < NR_SCANSTATS; i++)
    > +               cb->fill(cb, total_scanstat_string[i],
    > +                       mem->scanstat.totalstats[i]);
    > +       return 0;
    > +}
    > +
    > +static int mem_cgroup_reset_scan_stat(struct cgroup *cgrp,
    > +                               unsigned int event)
    > +{
    > +       struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
    > +
    > +       spin_lock(&mem->scanstat.lock);
    > +       memset(&mem->scanstat.stats, 0, sizeof(mem->scanstat.stats));
    > +       memset(&mem->scanstat.totalstats, 0, sizeof(mem->scanstat.totalstats));
    > +       spin_unlock(&mem->scanstat.lock);
    > +       return 0;
    > +}
    > +
    > +
    >  static struct cftype mem_cgroup_files[] = {
    >        {
    >                .name = "usage_in_bytes",
    > @@ -4669,6 +4786,11 @@ static struct cftype mem_cgroup_files[]
    >                .mode = S_IRUGO,
    >        },
    >  #endif
    > +       {
    > +               .name = "scan_stat",
    > +               .read_map = mem_cgroup_scan_stat_read,
    > +               .trigger = mem_cgroup_reset_scan_stat,
    > +       },
    >  };
    >
    >  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
    > @@ -4932,6 +5054,7 @@ mem_cgroup_create(struct cgroup_subsys *
    >        atomic_set(&mem->refcnt, 1);
    >        mem->move_charge_at_immigrate = 0;
    >        mutex_init(&mem->thresholds_lock);
    > +       spin_lock_init(&mem->scanstat.lock);
    >        return &mem->css;
    >  free_out:
    >        __mem_cgroup_free(mem);
    > Index: mmotm-0615/mm/vmscan.c
    > ===================================================================
    > --- mmotm-0615.orig/mm/vmscan.c
    > +++ mmotm-0615/mm/vmscan.c
    > @@ -2199,9 +2199,9 @@ unsigned long try_to_free_pages(struct z
    >  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
    >
    >  unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
    > -                                               gfp_t gfp_mask, bool noswap,
    > -                                               struct zone *zone,
    > -                                               unsigned long *nr_scanned)
    > +                                       gfp_t gfp_mask, bool noswap,
    > +                                       struct zone *zone,
    > +                                       struct memcg_scanrecord *rec)
    >  {
    >        struct scan_control sc = {
    >                .nr_scanned = 0,
    > @@ -2213,6 +2213,7 @@ unsigned long mem_cgroup_shrink_node_zon
    >                .order = 0,
    >                .mem_cgroup = mem,
    >        };
    > +       unsigned long start, end;
    >
    >        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    >                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
    > @@ -2221,6 +2222,7 @@ unsigned long mem_cgroup_shrink_node_zon
    >                                                      sc.may_writepage,
    >                                                      sc.gfp_mask);
    >
    > +       start = sched_clock();
    >        /*
    >         * NOTE: Although we can get the priority field, using it
    >         * here is not a good idea, since it limits the pages we can scan.
    > @@ -2229,19 +2231,27 @@ unsigned long mem_cgroup_shrink_node_zon
    >         * the priority and make it zero.
    >         */
    >        shrink_zone(0, zone, &sc);
    > +       end = sched_clock();
    > +
    > +       if (rec) {
    > +               rec->nr_scanned += sc.nr_scanned;
    > +               rec->nr_freed += sc.nr_reclaimed;
    > +               rec->elappsed += end - start;
    > +       }
    >
    >        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
    >
    > -       *nr_scanned = sc.nr_scanned;
    >        return sc.nr_reclaimed;
    >  }
    >
    >  unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    >                                           gfp_t gfp_mask,
    > -                                          bool noswap)
    > +                                          bool noswap,
    > +                                          struct memcg_scanrecord *rec)
    >  {
    >        struct zonelist *zonelist;
    >        unsigned long nr_reclaimed;
    > +       unsigned long start, end;
    >        int nid;
    >        struct scan_control sc = {
    >                .may_writepage = !laptop_mode,
    > @@ -2259,6 +2269,7 @@ unsigned long try_to_free_mem_cgroup_pag
    >                .gfp_mask = sc.gfp_mask,
    >        };
    >
    > +       start = sched_clock();
    >        /*
    >         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
    >         * take care of from where we get pages. So the node where we start the
    > @@ -2273,6 +2284,12 @@ unsigned long try_to_free_mem_cgroup_pag
    >                                            sc.gfp_mask);
    >
    >        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
    > +       end = sched_clock();
    > +       if (rec) {
    > +               rec->nr_scanned += sc.nr_scanned;
    > +               rec->nr_freed += sc.nr_reclaimed;
    > +               rec->elappsed += end - start;
    > +       }
    >
    >        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
    >
    >
    >
    --
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