linux-kernel - Re: [RFC][PATCH] memcg: page fault oom improvement v2

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Message-Id: <20100224112513.3d3e385b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 24 Feb 2010 11:25:13 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] memcg: page fault oom improvement v2

On Tue, 23 Feb 2010 18:26:17 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 24 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > > > > 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.
> > > > 
> > > 
> > > If you develop on top of my oom killer rewrite, pagefault ooms already 
> > > attempt to kill current first and then defer back to killing another task 
> > > if current is unkillable.  
> > 
> > After my fix, page_fault_out_of_memory is never called. (because memcg doesn't
> > return needless failure.)
> > 
> 
> Of course it's called, it's called from the pagefault handler whenever we 
> return VM_FAULT_OOM.  Whenever that happens, we'd needlessly panic the 
> machine for panic_on_oom if we didn't do the tasklist scan and check for 
> eligible tasks with TIF_MEMDIE set because it prefers to kill current 
> first in pagefault conditions without consideration given to the sysctl.  
> pagefault_out_of_memory() has changed radically with my rewrite, so I'd 
> encourage you to develop on top of that where I've completely removed 
> mem_cgroup_oom_called() and memcg->last_oom_jiffies already because 
> they're nonsense.
> 
> My patches are available from 
> http://www.kernel.org/pub/linux/kernel/people/rientjes/oom-killer-rewrite
> 

I do by myself.

Bye.
-Kame

> Thanks.
> 

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