linux-kernel - Re: [PATCH 1/3] doc: memcontrol: fix the obsolete content about force empty

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Date:   Thu, 3 Jan 2019 11:13:02 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     hannes@...xchg.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] doc: memcontrol: fix the obsolete content about
 force empty

On Thu 03-01-19 04:05:31, Yang Shi wrote:
> We don't do page cache reparent anymore when offlining memcg, so update
> force empty related content accordingly.
> 
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

Thanks for the clean up.

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

> ---
>  Documentation/cgroup-v1/memory.txt | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/cgroup-v1/memory.txt b/Documentation/cgroup-v1/memory.txt
> index 3682e99..8e2cb1d 100644
> --- a/Documentation/cgroup-v1/memory.txt
> +++ b/Documentation/cgroup-v1/memory.txt
> @@ -70,7 +70,7 @@ Brief summary of control files.
>   memory.soft_limit_in_bytes	 # set/show soft limit of memory usage
>   memory.stat			 # show various statistics
>   memory.use_hierarchy		 # set/show hierarchical account enabled
> - memory.force_empty		 # trigger forced move charge to parent
> + memory.force_empty		 # trigger forced page reclaim
>   memory.pressure_level		 # set memory pressure notifications
>   memory.swappiness		 # set/show swappiness parameter of vmscan
>  				 (See sysctl's vm.swappiness)
> @@ -459,8 +459,9 @@ About use_hierarchy, see Section 6.
>    the cgroup will be reclaimed and as many pages reclaimed as possible.
>  
>    The typical use case for this interface is before calling rmdir().
> -  Because rmdir() moves all pages to parent, some out-of-use page caches can be
> -  moved to the parent. If you want to avoid that, force_empty will be useful.
> +  Though rmdir() offlines memcg, but the memcg may still stay there due to
> +  charged file caches. Some out-of-use page caches may keep charged until
> +  memory pressure happens. If you want to avoid that, force_empty will be useful.
>  
>    Also, note that when memory.kmem.limit_in_bytes is set the charges due to
>    kernel pages will still be seen. This is not considered a failure and the
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs