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: <516E446B.5060006@gmail.com>
Date:	Wed, 17 Apr 2013 14:42:51 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	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

Hi Naoya,
On 04/11/2013 11:23 PM, Naoya Horiguchi wrote:
> 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.

The user applications will get EIO firstly or get SIG_KILL firstly?

> 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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