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

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Message-Id: <200905072218.50782.rjw@sisk.pl>
Date:	Thu, 7 May 2009 22:18:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 Thursday 07 May 2009, Andrew Morton wrote:
> On Thu, 7 May 2009 21:33:47 +0200
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > On Thursday 07 May 2009, Andrew Morton wrote:
> > > On Thu, 7 May 2009 20:09:52 +0200
> > > "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> > > 
> > > > > > > I'm suspecting that hibernation can allocate its pages with
> > > > > > > __GFP_FS|__GFP_WAIT|__GFP_NORETRY|__GFP_NOWARN, and the page allocator
> > > > > > > will dtrt: no oom-killings.
> > > > > > > 
> > > > > > > In which case, processes_are_frozen() is not needed at all?
> > > > > > 
> > > > > > __GFP_NORETRY alone causes it to fail relatively quickly, but I'll try with
> > > > > > the combination.
> > > > > 
> > > > > OK.  __GFP_WAIT is the big hammer.
> > > > 
> > > > Unfortunately it fails too quickly with the combination as well, so it looks
> > > > like we can't use __GFP_NORETRY during hibernation.
> > > 
> > > hm.
> > > 
> > > So where do we stand now?
> > > 
> > > I'm not a big fan of the global application-specific state change
> > > thing.  Something like __GFP_NO_OOM_KILL has a better chance of being
> > > reused by other subsystems in the future, which is a good indicator.
> > 
> > I'm not against __GFP_NO_OOM_KILL, but there's been some strong resistance to
> > adding new _GPF _FOO flags recently.
> 
> We have six or seven left - hardly a crisis.
> 
> >  Is there any likelihood anyone else we'll
> > really need it any time soon?
> 
> Dunno - people do all sorts of crazy things.  But it's more likely to
> be reused than a PM-specific global!
> 
> I have no strong feelings really, but slotting into the existing
> technique with something which might be reusable is quite a bit tidier.

OK, let's try with __GFP_NO_OOM_KILL first.  If there's too much disagreement,
I'll use the freezer-based approach instead.
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