linux-kernel - Re: [PATCH 00/13] Swap-over-NBD without deadlocking

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Date:	Thu, 28 Apr 2011 14:42:35 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Pavel Machek <pavel@....cz>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 00/13] Swap-over-NBD without deadlocking

On Thu, Apr 28, 2011 at 03:31:55PM +0200, Pavel Machek wrote:
> Hi!
> 
> 
> > For testing swap-over-NBD, a machine was booted with 2G of RAM with a
> > swapfile backed by NBD. 16*NUM_CPU processes were started that create
> > anonymous memory mappings and read them linearly in a loop. The total
> > size of the mappings were 4*PHYSICAL_MEMORY to use swap heavily under
> > memory pressure. Without the patches, the machine locks up within
> > minutes and runs to completion with them applied.
> > 
> > Comments?
> 
> Nice!
> 
> It  is easy to see why swapping needs these fixes, but... dirty memory
> writeout is used for memory clearing, too. Are same changes neccessary
> to make that safe?
> 

Dirty page limiting covers the MAP_SHARED cases and are already
throttled approprately.

> (Perhaps raise 'max dirty %' for testing?)

Stress testing passed for dirty ratios of 40% at least. Maybe it would
cause issues when raised to nearly 100% but I don't think that is a
particularly interesting use case.

-- 
Mel Gorman
SUSE Labs
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