linux-kernel - Re: [PATCH v8 05/17] mm: Assign memcg-aware shrinkers bitmap to memcg

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Message-Id: <20180705151030.c67eb9a989c5f0023a53d415@linux-foundation.org>
Date:   Thu, 5 Jul 2018 15:10:30 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     vdavydov.dev@...il.com, shakeelb@...gle.com,
        viro@...iv.linux.org.uk, hannes@...xchg.org, mhocko@...nel.org,
        tglx@...utronix.de, pombredanne@...b.com, stummala@...eaurora.org,
        gregkh@...uxfoundation.org, sfr@...b.auug.org.au, guro@...com,
        mka@...omium.org, penguin-kernel@...ove.SAKURA.ne.jp,
        chris@...is-wilson.co.uk, longman@...hat.com, minchan@...nel.org,
        ying.huang@...el.com, mgorman@...hsingularity.net, jbacik@...com,
        linux@...ck-us.net, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, willy@...radead.org, lirongqing@...du.com,
        aryabinin@...tuozzo.com
Subject: Re: [PATCH v8 05/17] mm: Assign memcg-aware shrinkers bitmap to
 memcg

On Wed, 4 Jul 2018 18:51:12 +0300 Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> > - why aren't we decreasing shrinker_nr_max in
> >   unregister_memcg_shrinker()?  That's easy to do, avoids pointless
> >   work in shrink_slab_memcg() and avoids memory waste in future
> >   prealloc_memcg_shrinker() calls.
> 
> You sure, but there are some things. Initially I went in the same way
> as memcg_nr_cache_ids is made and just took the same x2 arithmetic.
> It never decreases, so it looked good to make shrinker maps like it.
> It's the only reason, so, it should not be a problem to rework.
> 
> The only moment is Vladimir strongly recommends modularity, i.e.
> to have memcg_shrinker_map_size and shrinker_nr_max as different variables.

For what reasons?

> After the rework we won't be able to have this anymore, since memcontrol.c
> will have to know actual shrinker_nr_max value and it will have to be exported.
>
> Could this be a problem?

Vladimir?