linux-kernel - Re: [PATCH 02/10] mm: Maintain memcg-aware shrinkers in mcg

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Date:   Sat, 24 Mar 2018 21:45:16 +0300
From:   Vladimir Davydov <vdavydov.dev@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     viro@...iv.linux.org.uk, hannes@...xchg.org, mhocko@...nel.org,
        akpm@...ux-foundation.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,
        hillf.zj@...baba-inc.com, ying.huang@...el.com,
        mgorman@...hsingularity.net, shakeelb@...gle.com, jbacik@...com,
        linux@...ck-us.net, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, willy@...radead.org
Subject: Re: [PATCH 02/10] mm: Maintain memcg-aware shrinkers in
 mcg_shrinkers array

On Wed, Mar 21, 2018 at 04:21:29PM +0300, Kirill Tkhai wrote:
> The patch introduces mcg_shrinkers array to keep memcg-aware
> shrinkers in order of their shrinker::id.
> 
> This allows to access the shrinkers dirrectly by the id,
> without iteration over shrinker_list list.

Why don't you simply use idr instead of ida? With idr you wouldn't need
the array mapping shrinker id to shrinker ptr. AFAIU you need this
mapping to look up the shrinker by id in shrink_slab. The latter doesn't
seem to be a hot path so using idr there should be acceptable. Since we
already have shrinker_rwsem, which is taken for reading by shrink_slab,
we wouldn't even need any additional locking for it.