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From:   Yang Shi <shy828301@gmail.com>
Date:   Tue, 9 Feb 2021 17:07:07 -0800
Message-ID: <CAHbLzkp6q60pGBGKB-H6k5YoCy8ZHcLVj4rrZOsXi3=jOfbGzQ@mail.gmail.com>
Subject: Re: [v7 PATCH 06/12] mm: vmscan: add shrinker_info_protected() helper
To:     Roman Gushchin <guro@fb.com>
Cc:     Kirill Tkhai <ktkhai@virtuozzo.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Shakeel Butt <shakeelb@google.com>,
        Dave Chinner <david@fromorbit.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Feb 9, 2021 at 4:22 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Feb 09, 2021 at 09:46:40AM -0800, Yang Shi wrote:
> > The shrinker_info is dereferenced in a couple of places via rcu_dereference_protected
> > with different calling conventions, for example, using mem_cgroup_nodeinfo helper
> > or dereferencing memcg->nodeinfo[nid]->shrinker_info.  And the later patch
> > will add more dereference places.
> >
> > So extract the dereference into a helper to make the code more readable.  No
> > functional change.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  mm/vmscan.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 9436f9246d32..273efbf4d53c 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -190,6 +190,13 @@ static int shrinker_nr_max;
> >  #define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
> >       (DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
> >
> > +static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
> > +                                                  int nid)
> > +{
> > +     return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> > +                                      lockdep_is_held(&shrinker_rwsem));
> > +}
> > +
>
>
> I'd probably drop the "protected" suffix (because there is no unprotected version,
> right?).

No, actually there is one "unprotected" call in set_shrinker_bit().

>
> Other than that LGTM.
>
> Acked-by: Roman Gushchin <guro@fb.com>