linux-kernel - Re: [PATCH 1/5] mm: Add __GFP_NO_OOM

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Date:	Mon, 4 May 2009 09:44:46 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Wu Fengguang <fengguang.wu@...el.com>,
	linux-pm@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>, pavel@....cz,
	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

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).
--
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