linux-kernel - Re: [PATCH RFC 3/3] proc/smaps: show amount of hwpoison pages

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Message-ID: <CAHGf_=o_R8k-ywaAodrrHcnnjad01kp1szw_AuA-5AiB19fLew@mail.gmail.com>
Date:	Tue, 1 May 2012 14:14:57 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH RFC 3/3] proc/smaps: show amount of hwpoison pages

On Tue, May 1, 2012 at 2:05 PM, Konstantin Khlebnikov
<khlebnikov@...nvz.org> wrote:
> KOSAKI Motohiro wrote:
>>
>> On Mon, Apr 30, 2012 at 7:29 AM, Konstantin Khlebnikov
>> <khlebnikov@...nvz.org>  wrote:
>>>
>>> This patch adds line "HWPoinson:<size>  kB" into /proc/pid/smaps if
>>> CONFIG_MEMORY_FAILURE=y and some HWPoison pages were found.
>>> This may be useful for searching applications which use a broken memory.
>>
>>
>> I dislike "maybe useful" claim. If we don't know exact motivation of a
>> feature,
>> we can't maintain them especially when a bugfix can't avoid ABI change.
>>
>> Please write down exact use case.
>
> I don't know how to exactly use this hw-poison stuff, but smaps suppose to
> export state of ptes in vma. It seems to rational to show also hw-poisoned
> ptes,
> since kernel has this feature and pte can be in hw-poisoned state.
>
> and now everyone can easily find them:
> # sudo grep HWPoison /proc/*/smaps

First, I don't think "we can expose it" is good reason. Second, hw-poisoned mean
such process is going to be killed at next page touch. But I can't
imagine anyone can
use its information because it's racy against process kill. I think
admin should use mce log.

So, until we find a good use case, I don't ack this.
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