linux-kernel - Re: [v7 PATCH 09/12] mm: vmscan: use per memcg nr

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Date:   Wed, 10 Feb 2021 08:41:52 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        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: [v7 PATCH 09/12] mm: vmscan: use per memcg nr_deferred of shrinker

On Wed, Feb 10, 2021 at 6:37 AM Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
>
> On 10.02.2021 04:52, Yang Shi wrote:
> > On Tue, Feb 9, 2021 at 5:27 PM Roman Gushchin <guro@...com> wrote:
> >>
> >> On Tue, Feb 09, 2021 at 09:46:43AM -0800, Yang Shi wrote:
> >>> Use per memcg's nr_deferred for memcg aware shrinkers.  The shrinker's nr_deferred
> >>> will be used in the following cases:
> >>>     1. Non memcg aware shrinkers
> >>>     2. !CONFIG_MEMCG
> >>>     3. memcg is disabled by boot parameter
> >>>
> >>> Signed-off-by: Yang Shi <shy828301@...il.com>
> >>> ---
> >>>  mm/vmscan.c | 78 ++++++++++++++++++++++++++++++++++++++++++++---------
> >>>  1 file changed, 66 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> index d4b030a0b2a9..748aa6e90f83 100644
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -368,6 +368,24 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> >>>       up_write(&shrinker_rwsem);
> >>>  }
> >>>
> >>> +static long count_nr_deferred_memcg(int nid, struct shrinker *shrinker,
> >>> +                                 struct mem_cgroup *memcg)
> >>
> >> "Count" is not associated with xchg() semantics in my head, but I don't know
> >> what's the better version. Maybe steal or pop?
> >
> > It is used to retrieve the nr_deferred value. I don't think "steal" or
> > "pop" helps understand. Actually "count" is borrowed from
> > count_objects() method of shrinker.
>
> I'd also voted for another name.
>
> xchg_nr_deferred() or steal/pop sound better for me.

OK, I do have a hard time to understand steal/pop, but xchg sounds
more self-explained to me.

>