linux-kernel - Re: [PATCH mmotm] ksm: antidote to MADV

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Message-ID: <20090821184112.GB18623@basil.fritz.box>
Date:	Fri, 21 Aug 2009 20:41:12 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Izik Eidus <ieidus@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Kyle McMartin <kyle@...artin.ca>, Helge Deller <deller@....de>,
	Chris Zankel <chris@...kel.net>,
	Rik van RIel <riel@...hat.com>,
	Balbir Singh <balbir@...ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Avi Kivity <avi@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mmotm] ksm: antidote to MADV_MERGEABLE HWPOISON

On Fri, Aug 21, 2009 at 07:30:15PM +0100, Hugh Dickins wrote:
> linux-next is now sporting MADV_HWPOISON at 12, which would have a very
> nasty effect on KSM if you had CONFIG_MEMORY_FAILURE=y with CONFIG_KSM=y.
> Shift MADV_MERGEABLE and MADV_UNMERGEABLE down two - two to reduce the
> confusion if old and new userspace and kernel are mismatched.
> 
> Personally I'd prefer the MADV_HWPOISON testing feature to shift; but
> linux-next comes first in the mmotm lineup, and I can't be sure that
> madvise KSM already has more users than there are HWPOISON testers:
> so unless Andi is happy to shift MADV_HWPOISON, mmotm needs this.

Thanks for catching.

Shifting is fine, but I would prefer then if it was to some
value that is not reused (like 100) so that I can probe for it 
in the test programs.

-Andi
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