linux-kernel - Re: [v5 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr

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Date:   Fri, 29 Jan 2021 09:34:29 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Roman Gushchin <guro@...com>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Dave Chinner <david@...morbit.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: [v5 PATCH 09/11] mm: vmscan: don't need allocate
 shrinker->nr_deferred for memcg aware shrinkers

On Fri, Jan 29, 2021 at 7:40 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 1/28/21 12:33 AM, Yang Shi wrote:
> > Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need
> > allocate shrinker->nr_deferred for such shrinkers anymore.
> >
> > The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled
> > by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared.
> > This makes the implementation of this patch simpler.
> >
> > Signed-off-by: Yang Shi <shy828301@...il.com>
>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>
> > @@ -525,8 +528,20 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone
> >   */
> >  int prealloc_shrinker(struct shrinker *shrinker)
> >  {
> > -     unsigned int size = sizeof(*shrinker->nr_deferred);
> > +     unsigned int size;
> > +     int err;
> > +
> > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> > +             err = prealloc_memcg_shrinker(shrinker);
> > +             if (!err)
> > +                     return 0;
>
> Nit: this err == 0 case is covered below:

Aha, thanks. Will fix in v6.

>
> > +             if (err != -ENOSYS)
> > +                     return err;
> > +
> > +             shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
> > +     }
> >
> > +     size = sizeof(*shrinker->nr_deferred);
> >       if (shrinker->flags & SHRINKER_NUMA_AWARE)
> >               size *= nr_node_ids;
> >