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

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Date:	Sun, 10 May 2009 01:03:22 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, fengguang.wu@...el.com,
	linux-pm@...ts.linux-foundation.org, pavel@....cz,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	jens.axboe@...cle.com, alan-jenkins@...fmail.co.uk,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

On Sunday 10 May 2009, David Rientjes wrote:
> On Sat, 9 May 2009, Rafael J. Wysocki wrote:
> 
> > > This has been changed in the latest mmotm with Mel's page alloactor 
> > > patches (and I think yours should be based on mmotm).  Specifically, 
> > > page-allocator-break-up-the-allocator-entry-point-into-fast-and-slow-paths.patch.
> > > 
> > > Before his patchset, zonelists that had ZONE_OOM_LOCKED set for at least 
> > > one of their zones would unconditionally goto restart.  Now, if
> > > order > PAGE_ALLOC_COSTLY_ORDER, it gives up and returns NULL.  Otherwise, 
> > > it does goto restart.
> > > 
> > > So if your allocation has order > PAGE_ALLOC_COSTLY_ORDER,
> > 
> > It doesn't.  All of my allocations are of order 0.
> > 
> 
> All order 0 allocations are implicitly __GFP_NOFAIL and will loop 
> endlessly unless they can't block.  So if you want to simply prohibit the 
> oom killer from being invoked and not change the retry behavior, setting 
> ZONE_OOM_LOCKED for all zones will do that.  If your machine hangs, it 
> means nothing can be reclaimed and you can't free memory via oom killing, 
> so there's nothing else the page allocator can do.

But I want it to give up in this case instead of looping forever.

Look.  I have a specific problem at hand that I want to solve and the approach
you suggested _clearly_ _doesn't_ _work_.  I have also tried to explain to you
why it doesn't work, but you're ingnoring it, so I really don't know what else
I can say.

OTOH, the approach suggested by Andrew _does_ _work_ regardless of your
opinion about it.  It's been tested and it's done the job 100% of the time.  Go
figure.  And please stop beating the dead horse.

Thanks,
Rafael
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