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From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: linux-mm@kvack.org, YAMAMOTO Takashi <yamamoto@valinux.co.jp>,
	Paul Menage <menage@google.com>,
	lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	David Rientjes <rientjes@google.com>,
	Pavel Emelianov <xemul@openvz.org>,
	Dhaval Giani <dhaval@linux.vnet.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [mm] [PATCH 3/4] Memory cgroup hierarchical reclaim
Date: Thu, 06 Nov 2008 19:30:06 +0530	[thread overview]
Message-ID: <4912F866.9080009@linux.vnet.ibm.com> (raw)
In-Reply-To: <45571.10.75.179.62.1225902029.squirrel@webmail-b.css.fujitsu.com>

KAMEZAWA Hiroyuki wrote:
> Balbir Singh said:
>>>>>> +	list_for_each_entry_safe_from(cgroup, cg,
>>>>>> &cg_current->parent->children,
>>>>>> +						 sibling) {
>>>>>> +		mem_child = mem_cgroup_from_cont(cgroup);
>>>>>> +
>>>>>> +		/*
>>>>>> +		 * Move beyond last scanned child
>>>>>> +		 */
>>>>>> +		if (mem_child == mem->last_scanned_child)
>>>>>> +			continue;
>>>>>> +
>>>>>> +		ret = try_to_free_mem_cgroup_pages(mem_child, gfp_mask);
>>>>>> +		mem->last_scanned_child = mem_child;
>>>>>> +
>>>>>> +		if (res_counter_check_under_limit(&mem->res)) {
>>>>>> +			ret = 0;
>>>>>> +			goto done;
>>>>>> +		}
>>>>>> +	}
>>>>> Is this safe against cgroup create/remove ? cgroup_mutex is held ?
>>>> Yes, I thought about it, but with the setup, each parent will be busy
>>>> since they
>>>> have children and hence cannot be removed. The leaf child itself has
>>>> tasks, so
>>>> it cannot be removed. IOW, it should be safe against removal.
>>>>
>>> I'm sorry if I misunderstand something. could you explain folloing ?
>>>
>>> In following tree,
>>>
>>>     level-1
>>>          -  level-2
>>>                 -  level-3
>>>                        -  level-4
>>> level-1's usage = level-1 + level-2 + level-3 + level-4
>>> level-2's usage = level-2 + level-3 + level-4
>>> level-3's usage = level-3 + level-4
>>> level-4's usage = level-4
>>>
>>> Assume that a task in level-2 hits its limit. It has to reclaim memory
>>> from
>>> level-2 and level-3, level-4.
>>>
>>> How can we guarantee level-4 has a task in this case ?
>> Good question. If there is no task, the LRU's will be empty and reclaim
>> will
>> return. We could also add other checks if needed.
>>
> If needed ?, yes, you need.
> The problem is that you are walking a list in usual way without any lock
> or guarantee that the list will never be modified.
> 
> My quick idea is following.
> ==
> Before start reclaim.
>  1. take lock_cgroup()
>  2. scan the tree and create "private" list as snapshot of tree to be
>     scanned.

This might not be feasible, since we would need to recurse down tree structures.
I am wondering what is the best way to walk down a hierarchy, Paul any suggestions?

Here is what I have so far

1. take cgroup lock
2. list_for_each_safe.* to walk cgroup
3. Reclaim from local tasks
4. Reclaim from child cgroups (starting from last child we stopped at),
recursively, so that we can walk down the full hierarchy
5. unlock cgroup



-- 
	Balbir

  reply	other threads:[~2008-11-06 14:00 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-01 18:48 [mm][PATCH 0/4] Memory cgroup hierarchy introduction Balbir Singh
2008-11-01 18:48 ` [mm] [PATCH 1/4] Memory cgroup hierarchy documentation Balbir Singh
2008-11-04  6:25   ` Paul Menage
2008-11-04  6:26     ` Paul Menage
2008-11-05 13:55       ` Balbir Singh
2008-11-01 18:48 ` [mm] [PATCH 2/4] Memory cgroup resource counters for hierarchy Balbir Singh
2008-11-02  5:42   ` KAMEZAWA Hiroyuki
2008-11-02  5:49     ` Balbir Singh
2008-11-02  5:56       ` KAMEZAWA Hiroyuki
2008-11-02 11:46         ` Balbir Singh
2008-11-01 18:48 ` [mm] [PATCH 3/4] Memory cgroup hierarchical reclaim Balbir Singh
2008-11-02  5:37   ` KAMEZAWA Hiroyuki
2008-11-02  5:44     ` Balbir Singh
2008-11-04  2:17       ` KAMEZAWA Hiroyuki
2008-11-05 13:34         ` Balbir Singh
2008-11-05 16:20           ` KAMEZAWA Hiroyuki
2008-11-06 14:00             ` Balbir Singh [this message]
2008-11-01 18:49 ` [mm] [PATCH 4/4] Memory cgroup hierarchy feature selector Balbir Singh
2008-11-02  5:38   ` KAMEZAWA Hiroyuki
2008-11-02  6:03     ` Balbir Singh
2008-11-02  6:24       ` KAMEZAWA Hiroyuki
2008-11-02 15:52         ` Balbir Singh
2008-11-04  6:37           ` Paul Menage
2008-11-06  7:00             ` Balbir Singh
2008-11-06  7:01               ` Balbir Singh
2008-11-06  6:56         ` Balbir Singh
2008-11-06  7:30           ` KAMEZAWA Hiroyuki
2008-11-04  0:15 ` [mm][PATCH 0/4] Memory cgroup hierarchy introduction KAMEZAWA Hiroyuki
2008-11-05 13:51   ` Balbir Singh
2008-11-05 16:33     ` KAMEZAWA Hiroyuki
2008-11-05 17:52       ` Balbir Singh
2008-11-06  0:22         ` KAMEZAWA Hiroyuki
2008-11-04  9:21 ` [patch 1/2] memcg: hierarchy, yet another one KAMEZAWA Hiroyuki
2008-11-04  9:25 ` KAMEZAWA Hiroyuki

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