Re: [PATCH] mm: memcontrol: reset memory.low on css offline

[Michal Hocko <mhocko@kernel.org>]

On Mon 29-02-16 20:16:33, Vladimir Davydov wrote:
> When a cgroup directory is removed, the memory cgroup subsys state does
> not disappear immediately. Instead, it's left hanging around until the
> last reference to it is gone, which implies reclaiming all pages from
> its lruvec.
> 
> In the unified hierarchy, there's the memory.low knob, which can be used
> to set a best-effort protection for a memory cgroup - the reclaimer
> first scans those cgroups whose consumption is above memory.low, and
> only if it fails to reclaim enough pages, it gets to the rest.
> 
> Currently this protection is not reset when the cgroup directory is
> removed. As a result, if a dead memory cgroup has a lot of page cache
> charged to it and a high value of memory.low, it will result in higher
> pressure exerted on live cgroups, and userspace will have no ways to
> detect such consumers and reconfigure memory.low properly.
> 
> To fix this, let's reset memory.low on css offline.

Makes sense to me
 
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ae8b81c55685..ab7bfe870c7d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4214,6 +4214,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>  
>  	memcg_offline_kmem(memcg);
>  	wb_memcg_offline(memcg);
> +
> +	memcg->low = 0;
>  }
>  
>  static void mem_cgroup_css_released(struct cgroup_subsys_state *css)
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs

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