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

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Date:	Wed, 24 Feb 2010 10:48:39 +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 17:42:33 -0800 (PST)
David Rientjes <rientjes@...gle.com> 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.)

Then, that's not point in this thread.

Thanks,
-Kame

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