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Date: Fri, 20 Jan 2006 00:23:07 -0800
From: Andrew Morton <akpm@osdl.org>
To: Jens Axboe <axboe@suse.de>
Cc: davej@redhat.com, AChittenden@bluearc.com, linux-kernel@vger.kernel.org,
       lwoodman@redhat.com
Subject: Re: Out of Memory: Killed process 16498 (java).
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Jens Axboe <axboe@suse.de> wrote:
>
> On Thu, Jan 19 2006, Andrew Morton wrote:
> > Dave Jones <davej@redhat.com> wrote:
> > >
> > > On Thu, Jan 19, 2006 at 03:11:45PM -0000, Andy Chittenden wrote:
> > >  > DMA free:20kB min:24kB low:28kB high:36kB active:0kB inactive:0kB
> > >  > present:12740kB pages_scanned:4 all_unreclaimable? yes
> > > 
> > > Note we only scanned 4 pages before we gave up.
> > > Larry Woodman came up with this patch below that clears all_unreclaimable
> > > when in two places where we've made progress at freeing up some pages
> > > which has helped oom situations for some of our users.
> > 
> > That won't help - there are exactly zero pages on ZONE_DMA's LRU.
> > 
> > The problem appears to be that all of the DMA zone has been gobbled up by
> > the BIO layer.  It seems quite inappropriate that a modern 64-bit machine
> > is allocating tons of disk I/O pages from the teeny ZONE_DMA.  I'm
> > suspecting that someone has gone and set a queue's ->bounce_gfp to the wrong
> > thing.
> > 
> > Jens, would you have time to investigate please?
> 
> Certainly, I'll get this tested and fixed this afternoon.

Wow ;)

You may find it's an x86_64 glitch - setting max_[low_]pfn wrong down in
the bowels of the arch mm init code, something like that.

I thought it might have been a regression which came in when we added
ZONE_DMA32 but the RH reporter is based on 2.6.14-<redhat stuff>, and he
didn't have ZONE_DMA32.

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