linux-kernel - Re: [PATCH 1/5] HWPOISON: define VM_FAULT_HWPOISON to 0 when feature is disabled

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Date:	Fri, 12 Jun 2009 19:07:32 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andi Kleen <andi@...stfloor.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/5] HWPOISON: define VM_FAULT_HWPOISON to 0 when
 feature is disabled

> HWPOISON is a reliability enabling feature - if it enables prevalent
> of crappy hardwares, let's celebrate changing the world~~

HWPOISON is not in the most part a reliability enabling feature. Nothing
of the sort.

The existing behaviour is that your system goes kerblam on such a serious
error. The replacement behaviour is that bits of your machine go kerblam
in unpredictable ways.

In both cases you actually improve your reliability with clustering and
failover.

There are a few special cases its potentially useful - lots of VMs being
one where you have some chance of a controlled failure of a bounded
system. But even in that case I know if I was admin my scripts would read

   if (hwpoison_error)
        migrate_all_guests()
        mail admin
        schedule replacement of the machine

I'm not actually sure teaching hwpoison to handle anything but losing
entire guest OS systems is useful.
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