linux-kernel - Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG

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Date:   Thu, 5 Dec 2019 11:23:28 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, hannes@...xchg.org,
        mhocko@...e.com, shakeelb@...gle.com, guro@...com,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmscan: protect shrinker idr replace with
 CONFIG_MEMCG

On 04.12.2019 22:16, Yang Shi wrote:
> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> 
> Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Cc: Roman Gushchin <guro@...com>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

It looks like that in CONFIG_SLOB case we do not even call some shrinkers
for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
since they never become completely registered.

Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
Reviewed-by: Kirill Tkhai <ktkhai@...tuozzo.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ee4eecc..e7f10c4 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>  {
>  	down_write(&shrinker_rwsem);
>  	list_add_tail(&shrinker->list, &shrinker_list);
> -#ifdef CONFIG_MEMCG_KMEM
> +#ifdef CONFIG_MEMCG
>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>  #endif
>