linux-kernel - Re: [RFC] respect the referenced bit of KVM guest pages?

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Date:	Sat, 15 Aug 2009 13:32:08 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	"Dike, Jeffrey G" <jeffrey.g.dike@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Avi Kivity <avi@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Yu, Wilfred" <wilfred.yu@...el.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC] respect the referenced bit of KVM guest pages?

On Sat, Aug 15, 2009 at 06:37:22AM +0800, Rik van Riel wrote:
> Dike, Jeffrey G wrote:
> > A side note - I've been doing some tracing and shrink_active_list
> > is called a humongous number of times (25000-ish during a ~90 kvm
> > run), with a net result of zero pages moved nearly all the time.

Your mean "no pages get deactivated at all in most invocations"?
This is possible in the steady (thrashing) state of a memory tight
system(the working set is bigger than memory size). 

> > Your test is rescuing essentially all candidate pages from the
> > inactive list.  Right now, I have the VM_EXEC || PageAnon version
> > of your test.
> 
> That is exactly why the the split LRU VM does an unconditional
> deactivation of active anon pages :)

In general it is :)  However in Jeff's small memory case, there
will be many refaults without the "PageAnon" protection. But the
patch does not imply that I'm happy with the "PageAnon" test ;)

Thanks,
Fengguang
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