linux-kernel - Re: [mm][PATCH 0/4] Memory cgroup hierarchy introduction

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Date:	Wed, 05 Nov 2008 23:22:36 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	linux-mm@...ck.org, YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org,
	Nick Piggin <nickpiggin@...oo.com.au>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [mm][PATCH 0/4] Memory cgroup hierarchy introduction

KAMEZAWA Hiroyuki wrote:
> Balbir Singh said:
>> KAMEZAWA Hiroyuki wrote:
>>> On Sun, 02 Nov 2008 00:18:12 +0530
>>> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>> As first impression, I think hierarchical LRU management is not
>>> good...means
>>> not fair from viewpoint of memory management.
>> Could you elaborate on this further? Is scanning of children during
>> reclaim the
>> issue? Do you want weighted reclaim for each of the children?
>>
> No. Consider follwing case
>    /root/group_root/group_A
>                    /group_B
>                    /group_C
> 
>   sum of group A, B, C is limited by group_root's limit.
> 
>   Now,
>         /group_root limit=1G, usage=990M
>                     /group_A  usage=600M , no limit, no tasks for a while
>                     /group_B  usage=10M  , no limit, no tasks
>                     /group_C  usage=380M , no limit, 2 tasks
> 
>   A user run a new task in group_B.
>   In your algorithm, group_A and B and C's memory are reclaimed
>   to the same extent becasue there is no information to show
>   "group A's memory are not accessed recently rather than B or C".
> 
>   This information is what we want for managing memory.
> 

For that sort of implementation, we'll need a common LRU. I actually thought of
implementing it by sharing a common LRU, but then we would end up with just one
common LRU at the root :)

The reclaim algorithm is smart in that it knows what pages are commonly
accessed. group A will get reclaimed more since those pages are not actively
referenced. reclaim on group_C will be harder. Simple experiments seem to show that.


>>> I'd like to show some other possible implementation of
>>> try_to_free_mem_cgroup_pages() if I can.
>>>
>> Elaborate please!
>>
> ok. but, at least, please add
>   - per-subtree hierarchy flag.
>   - cgroup_lock to walk list of cgroups somewhere.
> 
> I already sent my version "shared LRU" just as a hint for you.
> It is something extreme but contains something good, I think.
> 
>>> Anyway, I have to merge this with mem+swap controller.
>> Cool! I'll send you an updated version.
>>
> 
> Synchronized LRU patch may help you.

Let me get a good working version against current -mm and then we'll integrate
our patches.

-- 
	Balbir
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