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

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Message-ID: <20090816031827.GA6888@localhost>
Date:	Sun, 16 Aug 2009 11:18:27 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Avi Kivity <avi@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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 Fri, Aug 07, 2009 at 05:09:55AM +0800, Jeff Dike wrote:
> Side question -
> 	Is there a good reason for this to be in shrink_active_list()
> as opposed to __isolate_lru_page?
> 
> 		if (unlikely(!page_evictable(page, NULL))) {
> 			putback_lru_page(page);
> 			continue;
> 		}
> 
> Maybe we want to minimize the amount of code under the lru lock or
> avoid duplicate logic in the isolate_page functions.

I guess the quick test means to avoid the expensive page_referenced()
call that follows it. But that should be mostly one shot cost - the
unevictable pages are unlikely to cycle in active/inactive list again
and again.

> But if there are important mlock-heavy workloads, this could make the
> scan come up empty, or at least emptier than we might like.

Yes, if the above 'if' block is removed, the inactive lists might get
more expensive to reclaim.

Thanks,
Fengguang
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