linux-kernel - Re: [RFC] Reproducible OOM with partial workaround

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Message-ID: <1357893007.1466.2.camel@kernel.cn.ibm.com>
Date:	Fri, 11 Jan 2013 02:30:07 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	paul.szabo@...ney.edu.au, dave@...ux.vnet.ibm.com,
	695182@...s.debian.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC] Reproducible OOM with partial workaround

On Fri, 2013-01-11 at 00:01 -0800, Andrew Morton wrote:
> On Fri, 11 Jan 2013 12:46:15 +1100 paul.szabo@...ney.edu.au wrote:
> 
> > > ... I don't believe 64GB of RAM has _ever_ been booted on a 32-bit
> > > kernel without either violating the ABI (3GB/1GB split) or doing
> > > something that never got merged upstream ...
> > 
> > Sorry to be so contradictory:
> > 
> > psz@...o:~$ uname -a
> > Linux como.maths.usyd.edu.au 3.2.32-pk06.10-t01-i386 #1 SMP Sat Jan 5 18:34:25 EST 2013 i686 GNU/Linux
> > psz@...o:~$ free -l
> >              total       used       free     shared    buffers     cached
> > Mem:      64446900    4729292   59717608          0      15972     480520
> > Low:        375836     304400      71436
> > High:     64071064    4424892   59646172
> > -/+ buffers/cache:    4232800   60214100
> > Swap:    134217724          0  134217724
> > psz@...o:~$ 
> > 
> > (though I would not know about violations).
> > 
> > But OK, I take your point that I should move with the times.
> 
> Check /proc/slabinfo, see if all your lowmem got eaten up by buffer_heads.
> 
> If so, you *may* be able to work around this by setting
> /proc/sys/vm/dirty_ratio really low, so the system keeps a minimum
> amount of dirty pagecache around.  Then, with luck, if we haven't
> broken the buffer_heads_over_limit logic it in the past decade (we
> probably have), the VM should be able to reclaim those buffer_heads.
> 
> Alternatively, use a filesystem which doesn't attach buffer_heads to
> dirty pages.  xfs or btrfs, perhaps.
> 

Hi Andrew,

What's the meaning of attaching buffer_heads to dirty pages?

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