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

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Date:	Thu, 7 May 2009 13:56:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	rientjes@...gle.com, fengguang.wu@...el.com,
	linux-pm@...ts.linux-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 Thu, 7 May 2009 22:38:13 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Thursday 07 May 2009, David Rientjes wrote:
> > On Thu, 7 May 2009, Rafael J. Wysocki wrote:
> > 
> > > OK, let's try with __GFP_NO_OOM_KILL first.  If there's too much disagreement,
> > > I'll use the freezer-based approach instead.
> > > 
> > 
> > Third time I'm going to suggest this, and I'd like a response on why it's 
> > not possible instead of being ignored.
> > 
> > All of your tasks are in D state other than kthreads, right?  That means 
> > they won't be in the oom killer (thus no zones are oom locked), so you can 
> > easily do this
> > 
> > 	struct zone *z;
> > 	for_each_populated_zone(z)
> > 		zone_set_flag(z, ZONE_OOM_LOCKED);
> > 
> > and then
> > 
> > 	for_each_populated_zone(z)
> > 		zone_clear_flag(z, ZONE_OOM_LOCKED);
> > 
> > The serialization is done with trylocks so this will never invoke the oom 
> > killer because all zones in the allocator's zonelist will be oom locked.
> > 
> > Why does this not work for you?
> 
> Well, it might work too, but why are you insisting?  How's it better than
> __GFP_NO_OOM_KILL, actually?
> 
> Andrew, what do you think about this?

I don't think I understand the proposal.  Is it to provide a means by
which PM can go in and set a state bit against each and every zone?  If
so, that's still a global boolean, only messier.
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