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Date: Mon, 4 May 2009 09:44:46 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
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To: "Rafael J. Wysocki" <rjw@sisk.pl>
cc: Wu Fengguang <fengguang.wu@intel.com>, linux-pm@lists.linux-foundation.org,
       Andrew Morton <akpm@linux-foundation.org>, pavel@ucw.cz,
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       alan-jenkins@tuffmail.co.uk, linux-kernel@vger.kernel.org,
       kernel-testers@vger.kernel.org
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag
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On Mon, 4 May 2009, Rafael J. Wysocki wrote:

> > > Index: linux-2.6/mm/page_alloc.c
> > > ===================================================================
> > > --- linux-2.6.orig/mm/page_alloc.c
> > > +++ linux-2.6/mm/page_alloc.c
> > > @@ -1620,7 +1620,8 @@ nofail_alloc:
> > >  		}
> > >  
> > >  		/* The OOM killer will not help higher order allocs so fail */
> > > -		if (order > PAGE_ALLOC_COSTLY_ORDER) {
> > > +		if (order > PAGE_ALLOC_COSTLY_ORDER ||
> > > +				(gfp_mask & __GFP_NO_OOM_KILL)) {
> > >  			clear_zonelist_oom(zonelist, gfp_mask);
> > >  			goto nopage;
> > >  		}
> > 
> > This is inconsistent because __GFP_NO_OOM_KILL now implies __GFP_NORETRY 
> > (the "goto nopage" above), but only for allocations with __GFP_FS set and 
> > __GFP_NORETRY clear.
> 
> Well, what would you suggest?
> 

A couple things:

 - rebase this on mmotm so that it doesn't conflict with Mel Gorman's page
   allocator speedup changes, and

 - avoid the final call to get_page_from_freelist() for 
   !(gfp_mask & __GFP_NO_OOM_KILL) by adding a check for it alongside 
   (gfp_mask & __GFP_FS) and !(gfp_mask & __GFP_NORETRY) because it should
   really only catch parallel oom killings which won't happen in your 
   suspend case since it uses ALLOC_WMARK_HIGH.

The latter is important to avoid unnecessary dependencies among low-level 
__GFP_* flags (although all __GFP_NO_OOM_KILL allocations should really 
all be passing __GFP_NORETRY too to avoid relying too heavily on direct 
reclaim).