linux-kernel - Re: [RFC Patch 0/2] mm: Add parameters to make kernel behavior at memory error on dirty cache selectable

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Message-ID: <1365693788-djsd2ymu-mutt-n-horiguchi@ah.jp.nec.com>
Date:	Thu, 11 Apr 2013 11:23:08 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Mitsuhiro Tanino <mitsuhiro.tanino.gm@...achi.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC Patch 0/2] mm: Add parameters to make kernel behavior at
 memory error on dirty cache selectable

On Thu, Apr 11, 2013 at 03:49:16PM +0200, Andi Kleen wrote:
> > As a result, if the dirty cache includes user data, the data is lost,
> > and data corruption occurs if an application uses old data.
> 
> The application cannot use old data, the kernel code kills it if it
> would do that. And if it's IO data there is an EIO triggered.
> 
> iirc the only concern in the past was that the application may miss
> the asynchronous EIO because it's cleared on any fd access. 
> 
> This is a general problem not specific to memory error handling, 
> as these asynchronous IO errors can happen due to other reason
> (bad disk etc.) 
> 
> If you're really concerned about this case I think the solution
> is to make the EIO more sticky so that there is a higher chance
> than it gets returned.  This will make your data much more safe,
> as it will cover all kinds of IO errors, not just the obscure memory
> errors.

I'm interested in this topic, and in previous discussion, what I was said
is that we can't expect user applications to change their behaviors when
they get EIO, so globally changing EIO's stickiness is not a great approach.
I'm working on a new pagecache tag based mechanism to solve this.
But it needs time and more discussions.
So I guess Tanino-san suggests giving up on dirty pagecache errors
as a quick solution.

Thanks,
Naoya
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