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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4A7AC201.4010202@redhat.com>
Date:	Thu, 06 Aug 2009 14:44:01 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	"Dike, Jeffrey G" <jeffrey.g.dike@...el.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 08/06/2009 01:59 PM, Wu Fengguang wrote:
>
> This is a quick hack to materialize the idea. It remembers roughly
> the last 32*SWAP_CLUSTER_MAX=1024 active (mapped) pages scanned,
> and if _all of them_ are referenced, then the referenced bit is
> probably meaningless and should not be taken seriously.
>
>    

I don't think we should ignore the referenced bit. There could still be 
a large batch of unreferenced pages later on that we should 
preferentially swap. If we swap at least 1 page for every 250 scanned, 
after 4K swaps we will have traversed 1M pages, enough to find them.

> As a refinement, the static variable 'recent_all_referenced' could be
> moved to struct zone or made a per-cpu variable.
>
>    

Definitely this should be made part of the zone structure, consider the 
original report where the problem occurs in a 128MB zone (where we can 
expect many pages to have their referenced bit set).

-- 
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/