linux-kernel - Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

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Message-Id: <20100215090949.169f2819.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 15 Feb 2010 09:09:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

On Fri, 12 Feb 2010 02:06:49 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Fri, 12 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > From viewpoint of panic-on-oom lover, this patch seems to cause regression.
> > please do this check after sysctl_panic_on_oom == 2 test.
> > I think it's easy. So, temporary Nack to this patch itself.
> > 
> > 
> > And I think calling notifier is not very bad in the situation.
> > ==
> > void out_of_memory()
> >  ..snip..
> >   blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
> > 
> > 
> > So,
> > 
> >         if (sysctl_panic_on_oom == 2) {
> >                 dump_header(NULL, gfp_mask, order, NULL);
> >                 panic("out of memory. Compulsory panic_on_oom is selected.\n");
> >         }
> > 
> > 	if (gfp_zone(gfp_mask) < ZONE_NORMAL) /* oom-kill is useless if lowmem is exhausted. */
> > 		return;
> > 
> > is better. I think.
> > 
> 
> I can't agree with that assessment, I don't think it's a desired result to 
> ever panic the machine regardless of what /proc/sys/vm/panic_on_oom is set 
> to because a lowmem page allocation fails especially considering, as 
> mentioned in the changelog, these allocations are never __GFP_NOFAIL and 
> returning NULL is acceptable.
> 
please add
  WARN_ON((high_zoneidx < ZONE_NORMAL) && (gfp_mask & __GFP_NOFAIL))
somewhere. Then, it seems your patch makes sense.

I don't like the "possibility" of inifinte loops.

Thanks,
-Kame



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