linux-kernel - Re: [RFC][PATCH 5/9 v2] move charges to root at rmdir if use

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Date:	Sat, 28 Apr 2012 09:01:23 +0900
From:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
To:	Ying Han <yinghan@...gle.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Tejun Heo <tj@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 5/9 v2] move charges to root at rmdir if
 use_hierarchy is unset

On Sat, Apr 28, 2012 at 4:12 AM, Ying Han <yinghan@...gle.com> wrote:
> On Thu, Apr 26, 2012 at 10:58 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
>> Now, at removal of cgroup, ->pre_destroy() is called and move charges
>> to the parent cgroup. A major reason of -EBUSY returned by ->pre_destroy()
>> is that the 'moving' hits parent's resource limitation. It happens only
>> when use_hierarchy=0. This was a mistake of original design.(it's me...)
>
> Nice patch, i can see how broken it is now with use_hierarchy=0...
>
> nitpick on the documentation below:
>
>>
>> Considering use_hierarchy=0, all cgroups are treated as flat. So, no one
>> cannot justify moving charges to parent...parent and children are in
>> flat configuration, not hierarchical.
>>
>> This patch modifes to move charges to root cgroup at rmdir/force_empty
>> if use_hierarchy==0. This will much simplify rmdir() and reduce error
>> in ->pre_destroy.
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> ---
>>  Documentation/cgroups/memory.txt |   12 ++++++----
>>  mm/memcontrol.c                  |   39 +++++++++++++------------------------
>>  2 files changed, 21 insertions(+), 30 deletions(-)
>>
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index 54c338d..82ce1ef 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
>> @@ -393,14 +393,14 @@ cgroup might have some charge associated with it, even though all
>>  tasks have migrated away from it. (because we charge against pages, not
>>  against tasks.)
>>
>> -Such charges are freed or moved to their parent. At moving, both of RSS
>> -and CACHES are moved to parent.
>> -rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also.
>> +Such charges are freed or moved to their parent if use_hierarchy=1.
>> +if use_hierarchy=0, the charges will be moved to root cgroup.
>
> It is more clear that we move the stats to root (if use_hierarchy==0)
> or parent (if use_hierarchy==1), and no change on the charge except
> uncharging from the child.
>

Seems nicer. I'll use your text in next ver.

Thanks,
-Kame
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