Re: [PATCH 5/7] memcg: divide force_empty into 2 functions, avoid memory reclaim at rmdir

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Ying Han <yinghan@google.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
	Michal Hocko <mhocko@suse.cz>,
	Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	Glauber Costa <glommer@parallels.com>,
	Hugh Dickins <hughd@google.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 5/7] memcg: divide force_empty into 2 functions, avoid memory reclaim at rmdir
Date: Wed, 18 Apr 2012 16:14:32 +0900	[thread overview]
Message-ID: <4F8E69D8.4070102@jp.fujitsu.com> (raw)
In-Reply-To: <CALWz4iwYX4r5dJmcKFuc+zj_rjMB76dtpbvArdzySF+dyxMohg@mail.gmail.com>

(2012/04/18 2:29), Ying Han wrote:

> On Thu, Apr 12, 2012 at 4:28 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> Now, at rmdir, memory cgroup's charge will be moved to
>>  - parent if use_hierarchy=1
>>  - root   if use_hierarchy=0
>>
>> Then, we don't have to have memory reclaim code at destroying memcg.
>>
>> This patch divides force_empty to 2 functions as
>>
>>  - memory_cgroup_recharge() ... try to move all charges to ancestors.
>>  - memory_cgroup_force_empty().. try to reclaim all memory.
>>
>> After this patch, memory.force_empty will _not_ move charges to ancestors
>> but just reclaim all pages. (This meets documenation.)
> 
> Not sure why it matches the documentation:
> "
> memory.force_empty>---->------- # trigger forced move charge to parent
> "

I missed this...

> 
> and
> "
>   # echo 0 > memory.force_empty
> 
>   Almost all pages tracked by this memory cgroup will be unmapped and freed.
>   Some pages cannot be freed because they are locked or in-use. Such pages are
>   moved to parent and this cgroup will be empty. This may return -EBUSY if
>   VM is too busy to free/move all pages immediately.
> "
> 

The 1st feature is "will be unmapped and freed".

I'll update Documentation. Thank you.

-Kame

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