linux-kernel - Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v5

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Date:	Wed, 10 Jun 2009 17:20:11 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	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>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] [13/16] HWPOISON: The high level memory error handler
	in the VM v5

On Wed, Jun 10, 2009 at 04:59:39PM +0800, Nick Piggin wrote:
> On Wed, Jun 10, 2009 at 04:38:03PM +0800, Wu Fengguang wrote:
> > On Wed, Jun 10, 2009 at 12:05:53AM +0800, Hugh Dickins wrote:
> > > I think a much more sensible approach would be to follow the page
> > > migration technique of replacing the page's ptes by a special swap-like
> > > entry, then do the killing from do_swap_page() if a process actually
> > > tries to access the page.
> > 
> > We call that "late kill" and will be enabled when
> > sysctl_memory_failure_early_kill=0. Its default value is 1.
> 
> What's the use of this? What are the tradeoffs, in what situations
> should an admin set this sysctl one way or the other?

Good questions.

My understanding is, when an application is generating data A, B, C in
sequence, and A is found to be corrupted by the kernel. Does it make
sense for the application to continue generate B and C? Or, are there
data dependencies between them? With late kill, it becomes more likely
that the disk contain new versions of B/C and old version of A, so
will more likely create data inconsistency.

So early kill is more safe.

Thanks,
Fengguang
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