Re: [patch 1/2] mm: memcg: per-memcg reclaim statistics

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Thank you for the patch and the stats looks reasonable to me, few
questions as below:

On Tue, Jan 10, 2012 at 7:02 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> With the single per-zone LRU gone and global reclaim scanning
> individual memcgs, it's straight-forward to collect meaningful and
> accurate per-memcg reclaim statistics.
>
> This adds the following items to memory.stat:

Some of the previous discussions including patches have similar stats
in memory.vmscan_stat API, which collects all the per-memcg vmscan
stats. I would like to understand more why we add into memory.stat
instead, and do we have plan to keep extending memory.stat for those
vmstat like stats?

>
> pgreclaim

Not sure if we want to keep this more consistent to /proc/vmstat, then
it will be "pgsteal"?

> pgscan
>
>  Number of pages reclaimed/scanned from that memcg due to its own
>  hard limit (or physical limit in case of the root memcg) by the
>  allocating task.
>
> kswapd_pgreclaim
> kswapd_pgscan

we have "pgscan_kswapd_*" in vmstat, so maybe ?
"pgsteal_kswapd"
"pgscan_kswapd"

>
>  Reclaim activity from kswapd due to the memcg's own limit.  Only
>  applicable to the root memcg for now since kswapd is only triggered
>  by physical limits, but kswapd-style reclaim based on memcg hard
>  limits is being developped.
>
> hierarchy_pgreclaim
> hierarchy_pgscan
> hierarchy_kswapd_pgreclaim
> hierarchy_kswapd_pgscan

"pgsteal_hierarchy"
"pgsteal_kswapd_hierarchy"
..

No strong option on the naming, but try to make it more consistent to
existing API.


>
>  Reclaim activity due to limitations in one of the memcg's parents.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
>  Documentation/cgroups/memory.txt |    4 ++
>  include/linux/memcontrol.h       |   10 +++++
>  mm/memcontrol.c                  |   84 +++++++++++++++++++++++++++++++++++++-
>  mm/vmscan.c                      |    7 +++
>  4 files changed, 103 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index cc0ebc5..eb9e982 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -389,6 +389,10 @@ mapped_file        - # of bytes of mapped file (includes tmpfs/shmem)
>  pgpgin         - # of pages paged in (equivalent to # of charging events).
>  pgpgout                - # of pages paged out (equivalent to # of uncharging events).
>  swap           - # of bytes of swap usage
> +pgreclaim      - # of pages reclaimed due to this memcg's limit
> +pgscan         - # of pages scanned due to this memcg's limit
> +kswapd_*       - # reclaim activity by background daemon due to this memcg's limit
> +hierarchy_*    - # reclaim activity due to pressure from parental memcg
>  inactive_anon  - # of bytes of anonymous memory and swap cache memory on
>                LRU list.
>  active_anon    - # of bytes of anonymous and swap cache memory on active
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index bd3b102..6c1d69e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -121,6 +121,8 @@ struct zone_reclaim_stat *mem_cgroup_get_reclaim_stat(struct mem_cgroup *memcg,
>                                                      struct zone *zone);
>  struct zone_reclaim_stat*
>  mem_cgroup_get_reclaim_stat_from_page(struct page *page);
> +void mem_cgroup_account_reclaim(struct mem_cgroup *, struct mem_cgroup *,
> +                               unsigned long, unsigned long, bool);
>  extern void mem_cgroup_print_oom_info(struct mem_cgroup *memcg,
>                                        struct task_struct *p);
>  extern void mem_cgroup_replace_page_cache(struct page *oldpage,
> @@ -347,6 +349,14 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
>        return NULL;
>  }
>
> +static inline void mem_cgroup_account_reclaim(struct mem_cgroup *root,
> +                                             struct mem_cgroup *memcg,
> +                                             unsigned long nr_reclaimed,
> +                                             unsigned long nr_scanned,
> +                                             bool kswapd)
> +{
> +}
> +
>  static inline void
>  mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
>  {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8e2a80d..170dff4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -91,12 +91,23 @@ enum mem_cgroup_stat_index {
>        MEM_CGROUP_STAT_NSTATS,
>  };
>
> +#define MEM_CGROUP_EVENTS_KSWAPD 2
> +#define MEM_CGROUP_EVENTS_HIERARCHY 4
> +
>  enum mem_cgroup_events_index {
>        MEM_CGROUP_EVENTS_PGPGIN,       /* # of pages paged in */
>        MEM_CGROUP_EVENTS_PGPGOUT,      /* # of pages paged out */
>        MEM_CGROUP_EVENTS_COUNT,        /* # of pages paged in/out */
>        MEM_CGROUP_EVENTS_PGFAULT,      /* # of page-faults */
>        MEM_CGROUP_EVENTS_PGMAJFAULT,   /* # of major page-faults */
> +       MEM_CGROUP_EVENTS_PGRECLAIM,
> +       MEM_CGROUP_EVENTS_PGSCAN,
> +       MEM_CGROUP_EVENTS_KSWAPD_PGRECLAIM,
> +       MEM_CGROUP_EVENTS_KSWAPD_PGSCAN,
> +       MEM_CGROUP_EVENTS_HIERARCHY_PGRECLAIM,
> +       MEM_CGROUP_EVENTS_HIERARCHY_PGSCAN,
> +       MEM_CGROUP_EVENTS_HIERARCHY_KSWAPD_PGRECLAIM,
> +       MEM_CGROUP_EVENTS_HIERARCHY_KSWAPD_PGSCAN,

missing comment here?
>        MEM_CGROUP_EVENTS_NSTATS,
>  };
>  /*
> @@ -889,6 +900,38 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
>        return (memcg == root_mem_cgroup);
>  }
>
> +/**
> + * mem_cgroup_account_reclaim - update per-memcg reclaim statistics
> + * @root: memcg that triggered reclaim
> + * @memcg: memcg that is actually being scanned
> + * @nr_reclaimed: number of pages reclaimed from @memcg
> + * @nr_scanned: number of pages scanned from @memcg
> + * @kswapd: whether reclaiming task is kswapd or allocator itself
> + */
> +void mem_cgroup_account_reclaim(struct mem_cgroup *root,
> +                               struct mem_cgroup *memcg,
> +                               unsigned long nr_reclaimed,
> +                               unsigned long nr_scanned,
> +                               bool kswapd)
> +{
> +       unsigned int offset = 0;
> +
> +       if (!root)
> +               root = root_mem_cgroup;
> +
> +       if (kswapd)
> +               offset += MEM_CGROUP_EVENTS_KSWAPD;
> +       if (root != memcg)
> +               offset += MEM_CGROUP_EVENTS_HIERARCHY;

Just to be clear, here root cgroup has hierarchy_* stats always 0 ?
Also, we might want to consider renaming the root here, something like
target? The root is confusing with root_mem_cgroup.

--Ying

> +
> +       preempt_disable();
> +       __this_cpu_add(memcg->stat->events[MEM_CGROUP_EVENTS_PGRECLAIM + offset],
> +                      nr_reclaimed);
> +       __this_cpu_add(memcg->stat->events[MEM_CGROUP_EVENTS_PGSCAN + offset],
> +                      nr_scanned);
> +       preempt_enable();
> +}
> +
>  void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
>  {
>        struct mem_cgroup *memcg;
> @@ -1662,6 +1705,8 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
>        excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;
>
>        while (1) {
> +               unsigned long nr_reclaimed;
> +
>                victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
>                if (!victim) {
>                        loop++;
> @@ -1687,8 +1732,11 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
>                }
>                if (!mem_cgroup_reclaimable(victim, false))
>                        continue;
> -               total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
> -                                                    zone, &nr_scanned);
> +               nr_reclaimed = mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
> +                                                          zone, &nr_scanned);
> +               mem_cgroup_account_reclaim(root_mem_cgroup, victim, nr_reclaimed,
> +                                          nr_scanned, current_is_kswapd());
> +               total += nr_reclaimed;
>                *total_scanned += nr_scanned;
>                if (!res_counter_soft_limit_excess(&root_memcg->res))
>                        break;
> @@ -4023,6 +4071,14 @@ enum {
>        MCS_SWAP,
>        MCS_PGFAULT,
>        MCS_PGMAJFAULT,
> +       MCS_PGRECLAIM,
> +       MCS_PGSCAN,
> +       MCS_KSWAPD_PGRECLAIM,
> +       MCS_KSWAPD_PGSCAN,
> +       MCS_HIERARCHY_PGRECLAIM,
> +       MCS_HIERARCHY_PGSCAN,
> +       MCS_HIERARCHY_KSWAPD_PGRECLAIM,
> +       MCS_HIERARCHY_KSWAPD_PGSCAN,
>        MCS_INACTIVE_ANON,
>        MCS_ACTIVE_ANON,
>        MCS_INACTIVE_FILE,
> @@ -4047,6 +4103,14 @@ struct {
>        {"swap", "total_swap"},
>        {"pgfault", "total_pgfault"},
>        {"pgmajfault", "total_pgmajfault"},
> +       {"pgreclaim", "total_pgreclaim"},
> +       {"pgscan", "total_pgscan"},
> +       {"kswapd_pgreclaim", "total_kswapd_pgreclaim"},
> +       {"kswapd_pgscan", "total_kswapd_pgscan"},
> +       {"hierarchy_pgreclaim", "total_hierarchy_pgreclaim"},
> +       {"hierarchy_pgscan", "total_hierarchy_pgscan"},
> +       {"hierarchy_kswapd_pgreclaim", "total_hierarchy_kswapd_pgreclaim"},
> +       {"hierarchy_kswapd_pgscan", "total_hierarchy_kswapd_pgscan"},
>        {"inactive_anon", "total_inactive_anon"},
>        {"active_anon", "total_active_anon"},
>        {"inactive_file", "total_inactive_file"},
> @@ -4079,6 +4143,22 @@ mem_cgroup_get_local_stat(struct mem_cgroup *memcg, struct mcs_total_stat *s)
>        s->stat[MCS_PGFAULT] += val;
>        val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_PGMAJFAULT);
>        s->stat[MCS_PGMAJFAULT] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_PGRECLAIM);
> +       s->stat[MCS_PGRECLAIM] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_PGSCAN);
> +       s->stat[MCS_PGSCAN] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_KSWAPD_PGRECLAIM);
> +       s->stat[MCS_KSWAPD_PGRECLAIM] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_KSWAPD_PGSCAN);
> +       s->stat[MCS_KSWAPD_PGSCAN] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_HIERARCHY_PGRECLAIM);
> +       s->stat[MCS_HIERARCHY_PGRECLAIM] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_HIERARCHY_PGSCAN);
> +       s->stat[MCS_HIERARCHY_PGSCAN] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_HIERARCHY_KSWAPD_PGRECLAIM);
> +       s->stat[MCS_HIERARCHY_KSWAPD_PGRECLAIM] += val;
> +       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_HIERARCHY_KSWAPD_PGSCAN);
> +       s->stat[MCS_HIERARCHY_KSWAPD_PGSCAN] += val;
>
>        /* per zone stat */
>        val = mem_cgroup_nr_lru_pages(memcg, BIT(LRU_INACTIVE_ANON));
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c631234..e3fd8a7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2115,12 +2115,19 @@ static void shrink_zone(int priority, struct zone *zone,
>
>        memcg = mem_cgroup_iter(root, NULL, &reclaim);
>        do {
> +               unsigned long nr_reclaimed = sc->nr_reclaimed;
> +               unsigned long nr_scanned = sc->nr_scanned;
>                struct mem_cgroup_zone mz = {
>                        .mem_cgroup = memcg,
>                        .zone = zone,
>                };
>
>                shrink_mem_cgroup_zone(priority, &mz, sc);
> +
> +               mem_cgroup_account_reclaim(root, memcg,
> +                                          sc->nr_reclaimed - nr_reclaimed,
> +                                          sc->nr_scanned - nr_scanned,
> +                                          current_is_kswapd());
>                /*
>                 * Limit reclaim has historically picked one memcg and
>                 * scanned it with decreasing priority levels until
> --
> 1.7.7.5
>

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