linux-kernel - Re: [PATCH 03/10] mm: Assign memcg-aware shrinkers bitmap to memcg

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Date:   Wed, 21 Mar 2018 07:56:25 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     viro@...iv.linux.org.uk, hannes@...xchg.org, mhocko@...nel.org,
        vdavydov.dev@...il.com, 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
Subject: Re: [PATCH 03/10] mm: Assign memcg-aware shrinkers bitmap to memcg

On Wed, Mar 21, 2018 at 04:21:40PM +0300, Kirill Tkhai wrote:
> +++ b/include/linux/memcontrol.h
> @@ -151,6 +151,11 @@ struct mem_cgroup_thresholds {
>  	struct mem_cgroup_threshold_ary *spare;
>  };
>  
> +struct shrinkers_map {
> +	struct rcu_head rcu;
> +	unsigned long *map[0];
> +};
> +
>  enum memcg_kmem_state {
>  	KMEM_NONE,
>  	KMEM_ALLOCATED,
> @@ -182,6 +187,9 @@ struct mem_cgroup {
>  	unsigned long low;
>  	unsigned long high;
>  
> +	/* Bitmap of shrinker ids suitable to call for this memcg */
> +	struct shrinkers_map __rcu *shrinkers_map;
> +
>  	/* Range enforcement for interrupt charges */
>  	struct work_struct high_work;
>  

Why use your own bitmap here?  Why not use an IDA which can grow and
shrink automatically without you needing to play fun games with RCU?