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From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Date: Tue, 1 May 2012 14:14:57 -0400
Message-ID: <CAHGf_=o_R8k-ywaAodrrHcnnjad01kp1szw_AuA-5AiB19fLew@mail.gmail.com>
Subject: Re: [PATCH RFC 3/3] proc/smaps: show amount of hwpoison pages
To: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>
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On Tue, May 1, 2012 at 2:05 PM, Konstantin Khlebnikov
<khlebnikov@openvz.org> wrote:
> KOSAKI Motohiro wrote:
>>
>> On Mon, Apr 30, 2012 at 7:29 AM, Konstantin Khlebnikov
>> <khlebnikov@openvz.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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