linux-kernel - Re: [patch 2/4] mm, oom: cleanup pagefault oom handler

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Message-ID: <alpine.DEB.2.00.1211151257500.27188@chino.kir.corp.google.com>
Date:	Thu, 15 Nov 2012 13:01:23 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 2/4] mm, oom: cleanup pagefault oom handler

On Thu, 15 Nov 2012, Kamezawa Hiroyuki wrote:

> > @@ -708,15 +671,17 @@ out:
> > 
> >   /*
> >    * The pagefault handler calls here because it is out of memory, so kill a
> > - * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a
> > parallel
> > - * oom killing is already in progress so do nothing.  If a task is found
> > with
> > - * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
> > + * memory-hogging task.  If any populated zone has ZONE_OOM_LOCKED set, a
> > + * parallel oom killing is already in progress so do nothing.
> >    */
> >   void pagefault_out_of_memory(void)
> >   {
> > -	if (try_set_system_oom()) {
> > +	struct zonelist *zonelist = node_zonelist(first_online_node,
> > +						  GFP_KERNEL);
> 
> 
> why GFP_KERNEL ? not GFP_HIGHUSER_MOVABLE ?
> 

The usual way to get a zonelist consisting of all zones ordered by 
preferring a node is node_zonelist(nid, GFP_KERNEL), but there's no 
difference between using GFP_KERNEL, GFP_HIGHUSER_MOVABLE, or even 0.  I 
simply duplicated what the sysrq trigger was doing, but you could also do 
&first_online_pgdat->node_zonelists[0], it's really just a matter of 
preference.
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