Date: Wed, 24 Feb 2010 09:08:36 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: David Rientjes <rientjes@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
       Balbir Singh <balbir@linux.vnet.ibm.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] memcg: page fault oom improvement v2
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On Tue, 23 Feb 2010 14:49:12 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> On Tue, 23 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > Ouch, I missed to add memcontrol.h to quilt's reflesh set..
> > This is updated one. Anyway, I'd like to wait for the next mmotm.
> > We already have several changes. 
> > 
> 
> I think it would be better to just remove mem_cgroup_out_of_memory() and 
> make it go through out_of_memory() by specifying a non-NULL pointer to a 
> struct mem_cgroup.  We don't need the duplication in code that these two 
> functions have and then we can begin to have some consistency with how to 
> deal with panic_on_oom.
> 
> It would be much better to prefer killing current in pagefault oom 
> conditions, as the final patch in my oom killer rewrite does, if it is 
> killable.  If not, we scan the tasklist and find another suitable 
> candidate.  If current is bound to a memcg, we pass that to 
> select_bad_process() so that we only kill other tasks from the same 
> cgroup.
Adding new argument to out_of_memory ?

> 
> This allows us to hijack the TIF_MEMDIE bit to detect when there is a 
> parallel pagefault oom killing when the oom killer hasn't necessarily been 
> invoked to kill a system-wide task (it's simply killing current, by 
> default, and giving it access to memory reserves).  Then, we can change 
> out_of_memory(), which also now handles memcg oom conditions, to always 
> scan the tasklist first (including for mempolicy and cpuset constrained 
> ooms), check for any candidates that have TIF_MEMDIE, and return 
> ERR_PTR(-1UL) if so.  That catches the parallel pagefault oom conditions 
> from needlessly killing memcg tasks.  panic_on_oom would only panic after 
> the tasklist scan has completed and returned != ERR_PTR(-1UL), meaning 
> pagefault ooms are exempt from that sysctl.
> 
Sorry, I see your concern but I'd like not to do clean-up and bug-fix at
the same time.  

I think clean up after fix is easy in this case.


> Anyway, do you think it would be possible to rebase on mmotm with my oom 
> killer rewrite patches?  
> They're at 
> http://www.kernel.org/pub/linux/kernel/people/rientjes/oom-killer-rewrite
> 

I can wait until your patch are merged if necessary. But it seems there will
not be much confliction.


Thanks,
-Kame

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