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Date:   Fri, 23 Mar 2018 13:29:02 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     "Li,Rongqing" <lirongqing@baidu.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: =?utf-8?B?562U5aSNOiDnrZTlpI06IOetlA==?=
 =?utf-8?B?5aSNOiBbUEFUQ0g=?= =?utf-8?Q?=5D?= mm/memcontrol.c: speed up to
 force empty a memory cgroup
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On Fri 23-03-18 12:04:16, Li,Rongqing wrote:
[...]
> shrink_slab does not reclaim any memory, but take lots of time to
> count lru
>
> maybe we can use the returning of shrink_slab to control if next
> shrink_slab should be called?

How? Different memcgs might have different amount of shrinkable memory.

> Or define a slight list_lru_empty to check if sb->s_dentry_lru is
> empty before calling list_lru_shrink_count, like below

Does it really help to improve numbers?
 
> diff --git a/fs/super.c b/fs/super.c
> index 672538ca9831..954c22338833 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -130,8 +130,10 @@ static unsigned long super_cache_count(struct shrinker *shrink,
>         if (sb->s_op && sb->s_op->nr_cached_objects)
>                 total_objects = sb->s_op->nr_cached_objects(sb, sc);
>  
> -       total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
> -       total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
> +       if (!list_lru_empty(sb->s_dentry_lru))
> +               total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
> +       if (!list_lru_empty(sb->s_inode_lru))
> +               total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
>  
>         total_objects = vfs_pressure_ratio(total_objects);
>         return total_objects;

-- 
Michal Hocko
SUSE Labs