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Date:   Tue, 15 Dec 2020 15:10:28 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Roman Gushchin <guro@...com>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline

On Mon, Dec 14, 2020 at 7:08 PM Dave Chinner <david@...morbit.com> wrote:
>
> On Mon, Dec 14, 2020 at 02:37:21PM -0800, Yang Shi wrote:
> > Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add to parent's
> > corresponding nr_deferred when memcg offline.
> >
> > Signed-off-by: Yang Shi <shy828301@...il.com>
> > ---
> >  include/linux/shrinker.h |  4 ++++
> >  mm/memcontrol.c          | 24 ++++++++++++++++++++++++
> >  mm/vmscan.c              |  2 +-
> >  3 files changed, 29 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> > index 1eac79ce57d4..85cfc910dde4 100644
> > --- a/include/linux/shrinker.h
> > +++ b/include/linux/shrinker.h
> > @@ -78,6 +78,10 @@ struct shrinker {
> >  };
> >  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
> >
> > +#ifdef CONFIG_MEMCG
> > +extern int shrinker_nr_max;
> > +#endif
> > +
> >  /* Flags */
> >  #define SHRINKER_REGISTERED  (1 << 0)
> >  #define SHRINKER_NUMA_AWARE  (1 << 1)
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 321d1818ce3d..1f191a15bee1 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -59,6 +59,7 @@
> >  #include <linux/tracehook.h>
> >  #include <linux/psi.h>
> >  #include <linux/seq_buf.h>
> > +#include <linux/shrinker.h>
> >  #include "internal.h"
> >  #include <net/sock.h>
> >  #include <net/ip.h>
> > @@ -612,6 +613,28 @@ void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> >       }
> >  }
> >
> > +static void memcg_reparent_shrinker_deferred(struct mem_cgroup *memcg)
> > +{
> > +     int i, nid;
> > +     long nr;
> > +     struct mem_cgroup *parent;
> > +     struct memcg_shrinker_deferred *child_deferred, *parent_deferred;
> > +
> > +     parent = parent_mem_cgroup(memcg);
> > +     if (!parent)
> > +             parent = root_mem_cgroup;
> > +
> > +     for_each_node(nid) {
> > +             child_deferred = memcg->nodeinfo[nid]->shrinker_deferred;
> > +             parent_deferred = parent->nodeinfo[nid]->shrinker_deferred;
> > +             for (i = 0; i < shrinker_nr_max; i ++) {
> > +                     nr = atomic_long_read(&child_deferred->nr_deferred[i]);
> > +                     atomic_long_add(nr,
> > +                             &parent_deferred->nr_deferred[i]);
> > +             }
> > +     }
> > +}
>
> I would place this function in vmscan.c alongside the
> shrink_slab_set_nr_deferred_memcg() function so that all the
> accounting is in the one place.

Fine to me. Will incorporate in v3.

>
> > +
> >  /**
> >   * mem_cgroup_css_from_page - css of the memcg associated with a page
> >   * @page: page of interest
> > @@ -5543,6 +5566,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> >       page_counter_set_low(&memcg->memory, 0);
> >
> >       memcg_offline_kmem(memcg);
> > +     memcg_reparent_shrinker_deferred(memcg);
> >       wb_memcg_offline(memcg);
> >
> >       drain_all_stock(memcg);
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 8d5bfd818acd..693a41e89969 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -201,7 +201,7 @@ DECLARE_RWSEM(shrinker_rwsem);
> >  #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> >
> >  static DEFINE_IDR(shrinker_idr);
> > -static int shrinker_nr_max;
> > +int shrinker_nr_max;
>
> Then we don't need to make yet another variable global...
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@...morbit.com

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