linux-kernel - Re: [RFC][PATCH] memcg: page fault oom improvement

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Date:	Tue, 23 Feb 2010 11:40:20 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	rientjes@...gle.com, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] memcg: page fault oom improvement

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-02-23 12:03:15]:

> Nishimura-san, could you review and test your extreme test case with this ?
> 
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Now, because of page_fault_oom_kill, returning VM_FAULT_OOM means
> random oom-killer should be called. Considering memcg, it handles
> OOM-kill in its own logic, there was a problem as "oom-killer called
> twice" problem.
> 
> By commit a636b327f731143ccc544b966cfd8de6cb6d72c6, I added a check
> in pagefault_oom_killer shouldn't kill some (random) task if
> memcg's oom-killer already killed anyone.
> That was done by comapring current jiffies and last oom jiffies of memcg.
> 
> I thought that easy fix was enough, but Nishimura could write a test case
> where checking jiffies is not enough. So, my fix was not enough.
> This is a fix of above commit.
> 
> This new one does this.
>  * memcg's try_charge() never returns -ENOMEM if oom-killer is allowed.
>  * If someone is calling oom-killer, wait for it in try_charge().
>  * If TIF_MEMDIE is set as a result of try_charge(), return 0 and
>    allow process to make progress (and die.) 
>  * removed hook in pagefault_out_of_memory.
> 
> By this, pagefult_out_of_memory will be never called if memcg's oom-killer
> is called and scattered codes are now in memcg's charge logic again.
> 
> TODO:
>  If __GFP_WAIT is not specified in gfp_mask flag, VM_FAULT_OOM will return
>  anyway. We need to investigate it whether there is a case.
> 
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Balbir Singh <balbir@...ibm.com>
> Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

I've not reviewed David's latest OOM killer changes. Are these changes based on top of
what is going to come in with David's proposal?
-- 
	Three Cheers,
	Balbir
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