From: Yang Shi <shy828301@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>, Kirill Tkhai <ktkhai@virtuozzo.com>,
Shakeel Butt <shakeelb@google.com>,
Dave Chinner <david@fromorbit.com>,
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>
Subject: Re: [PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred
Date: Fri, 11 Dec 2020 09:52:42 -0800 [thread overview]
Message-ID: <CAHbLzkpwAANd_Nci5Krcek+NmexJCZVVQqSsJF6=xfLVsMK34Q@mail.gmail.com> (raw)
In-Reply-To: <CAHbLzkoSSQ_4aY1cNmJGZyL+r6yO3L41KWHi8ZQnDhFTNi-v_Q@mail.gmail.com>
On Thu, Dec 10, 2020 at 11:12 AM Yang Shi <shy828301@gmail.com> wrote:
>
> On Thu, Dec 10, 2020 at 7:36 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > On Wed, Dec 02, 2020 at 10:27:21AM -0800, Yang Shi wrote:
> > > @@ -504,6 +577,34 @@ int memcg_expand_shrinker_maps(int new_id)
> > > return ret;
> > > }
> > >
> > > +int memcg_expand_shrinker_deferred(int new_id)
> > > +{
> > > + int size, old_size, ret = 0;
> > > + struct mem_cgroup *memcg;
> > > +
> > > + size = (new_id + 1) * sizeof(atomic_long_t);
> > > + old_size = memcg_shrinker_deferred_size;
> > > + if (size <= old_size)
> > > + return 0;
> > > +
> > > + mutex_lock(&memcg_shrinker_mutex);
> >
> > The locking is somewhat confusing. I was wondering why we first read
> > memcg_shrinker_deferred_size "locklessly", then change it while
> > holding the &memcg_shrinker_mutex.
> >
> > memcg_shrinker_deferred_size only changes under shrinker_rwsem(write),
> > correct? This should be documented in a comment, IMO.
>
> Yes, it is correct.
>
> >
> > memcg_shrinker_mutex looks superfluous then. The memcg allocation path
> > is the read-side of memcg_shrinker_deferred_size, and so simply needs
> > to take shrinker_rwsem(read) to lock out shrinker (de)registration.
>
> I see you point. Yes, it seems shrinker_{maps|deferred} allocation
> could be synchronized with shrinker registration by shrinker_rwsem.
>
> memcg_shrinker_mutex is just renamed from memcg_shrinker_map_mutex
> which was introduced by shrinker_maps patchset. I'm not quite sure why
> this mutex was introduced at the first place, I guess the main purpose
> is to *not* exacerbate the contention of shrinker_rwsem?
>
> If that contention is not a concern, we could remove that dedicated mutex.
It seems using shrinker_rwsem instead of dedicated mutex should not
exacerbate the contention since we just add one read critical section.
Will do it in v2.
>
> >
> > Also, isn't memcg_shrinker_deferred_size just shrinker_nr_max? And
>
> No, it is variable. It is nr * sizeof(atomit_long_t). The nr is the
> current last shrinker ID. If a new shrinker is registered, the nr may
> grow.
>
> > memcg_expand_shrinker_deferred() is only called when size >= old_size
> > in the first place (because id >= shrinker_nr_max)?
>
> Yes.
next prev parent reply other threads:[~2020-12-11 19:34 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 18:27 [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Yang Shi
2020-12-02 18:27 ` [PATCH 1/9] mm: vmscan: simplify nr_deferred update code Yang Shi
2020-12-03 2:56 ` Roman Gushchin
2020-12-02 18:27 ` [PATCH 2/9] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2020-12-03 3:13 ` Xiaqing (A)
2020-12-11 19:20 ` Yang Shi
2020-12-02 18:27 ` [PATCH 3/9] mm: memcontrol: rename memcg_shrinker_map_mutex to memcg_shrinker_mutex Yang Shi
2020-12-02 18:27 ` [PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2020-12-03 3:01 ` Roman Gushchin
2020-12-03 4:59 ` Yang Shi
2020-12-03 20:08 ` Roman Gushchin
2020-12-03 22:25 ` Yang Shi
2020-12-04 18:52 ` Johannes Weiner
2020-12-04 21:24 ` Yang Shi
2020-12-02 18:27 ` [PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred Yang Shi
2020-12-03 3:06 ` Roman Gushchin
2020-12-03 4:54 ` Yang Shi
2020-12-03 18:03 ` Yang Shi
2020-12-03 20:07 ` Roman Gushchin
2020-12-03 22:49 ` Yang Shi
2020-12-03 23:30 ` Roman Gushchin
2020-12-04 0:22 ` Yang Shi
2020-12-10 15:33 ` Johannes Weiner
2020-12-10 19:12 ` Yang Shi
2020-12-11 17:52 ` Yang Shi [this message]
2020-12-10 21:59 ` Yang Shi
2020-12-02 18:27 ` [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2020-12-03 3:08 ` Roman Gushchin
2020-12-03 5:01 ` Yang Shi
2020-12-03 11:40 ` Kirill Tkhai
2020-12-08 17:13 ` Yang Shi
2020-12-09 15:41 ` Kirill Tkhai
2020-12-09 17:32 ` Yang Shi
2020-12-10 15:13 ` Johannes Weiner
2020-12-10 15:17 ` Kirill Tkhai
2020-12-15 16:44 ` Johannes Weiner
2020-12-02 18:27 ` [PATCH 7/9] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2020-12-02 18:27 ` [PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2020-12-02 18:27 ` [PATCH 9/9] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
2020-12-03 2:52 ` [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Roman Gushchin
2020-12-03 17:52 ` Yang Shi
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