linux-kernel - Re: [RFC Patch 2/2] mm: Add parameters to limit a rate of outputting memory error messages

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Date:	Fri, 12 Apr 2013 22:30:28 +0900
From:	Mitsuhiro Tanino <mitsuhiro.tanino.gm@...achi.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andi Kleen <andi@...stfloor.org>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC Patch 2/2] mm: Add parameters to limit a rate of outputting
 memory error messages

(2013/04/11 23:47), Naoya Horiguchi wrote:
> On Thu, Apr 11, 2013 at 04:00:12PM +0200, Andi Kleen wrote:
>>> I don't think it's enough to do ratelimit only for me_pagecache_dirty().
>>> When tons of memory errors flood, all of printk()s in memory error handler
>>> can print out tons of messages.
>>
>> Note that when you really have a flood of uncorrected errors you'll
>> likely die soon anyways as something unrecoverable is very likely to
>> happen. Error memory recovery cannot fix large scale memory corruptions,
>> just the rare events that slip through all the other memory error correction
>> schemes.
>>
>> So I wouldn't worry too much about that.
> 
> I agree.
> My previous comment is valid only when we assume the flooding can happen
> (and I personally don't believe that can happen except for in testing.)
> 
> And for paranoid users, we can suggest that they set up mcelog script
> triggering to turn off vm.memory_failure_recovery when memory errors flood.
> Such users don't expect that memory error handling works fine in flooding,
> so just suppressing kernel messages is pointless.
> 
> Thanks,
> Naoya

Hi Andi, Horiguchi-san, Kosaki-san

Thank you for your comments. I agree with your opinions.
I think that occurrence of uncorrected error is rare event, too.

I introduced a limitation feature using ratelimit in my patch in honor
of the previous discussion a half year ago. In the discussion, Andrew-san
threw a concern of a flood of uncorrected error for the patch proposed by
Horiguchi-san.

I think that ratelimit can be removed to output all "important messages".

I will try to resend patches sepalately, 
one is for outputting error messages related to a corrupted file
and the other is for adding a panic knob to handle data lost of dirty cache
which is caused by both memory error and I/O error.

Regards,
Mitsuhiro Tanino

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