Date: Sun, 14 Nov 2004 08:02:27 -0200
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: Andrea Arcangeli <andrea@novell.com>
Cc: Chris Ross <chris@tebibyte.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, Nick Piggin <piggin@cyberone.com.au>,
       Rik van Riel <riel@redhat.com>,
       Martin MOKREJ? <mmokrejs@ribosome.natur.cuni.cz>, tglx@linutronix.de
Subject: Re: [PATCH] fix spurious OOM kills
Message-ID: <20041114100227.GA2764@logos.cnet>
References: <20041111112922.GA15948@logos.cnet> <4193E056.6070100@tebibyte.org> <4194EA45.90800@tebibyte.org> <20041113233740.GA4121@x30.random> <20041114094417.GC29267@logos.cnet>
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On Sun, Nov 14, 2004 at 07:44:17AM -0200, Marcelo Tosatti wrote:
> On Sun, Nov 14, 2004 at 12:37:40AM +0100, Andrea Arcangeli wrote:
> > On Fri, Nov 12, 2004 at 05:52:21PM +0100, Chris Ross wrote:
> > > 
> > > 
> > > Chris Ross escreveu:
> > > >It seems good.
> > > 
> > > Sorry Marcelo, I spoke to soon. The oom killer still goes haywire even 
> > > with your new patch. I even got this one whilst the machine was booting!
> > 
> > On monday I'll make a patch to place the oom killer at the right place.
> > 
> > Marcelo's argument that kswapd is a localized place isn't sound to me,
> > kswapd is still racing against all other task contexts, so if the task
> > context isn't reliable, there's no reason why kswapd should be more
> > reliable than the task context. the trick is to check the _right_
> > watermarks before invoking the oom killer, it's not about racing against
> > each other, 2.6 is buggy in not checking the watermarks. Moving the oom
> > killer in kswapd can only make thing worse, fix is simple, and it's the
> > opposite thing: move the oom killer up the stack outside vmscan.c.
> 
> Its hard to detect OOM situation with zone->all_unreclaimable logic.
> 
> Well, I'll wait for your correct and definitive approach.

Take zone->all_unreclaimable into account when you move oom_kill in page_alloc.c, 
which I now think might be the simpler fix.

shrink_caches() will fail early due to all_unreclaimable() logic (it wont 
scan/writeout at lower priorities):

	if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
		continue;       /* Let kswapd poll it */

I disabled all_unreclaimable after 5 seconds allowed kswapd to scan
the full zone and reliably detect OOM in my kill-from-kswapd patch - 
you might want something similar.

That seems one the main reasons for the spurious OOM kills.

Anxious to see your patch! 

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