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: <51680F97.3020407@hitachi.com>
Date:	Fri, 12 Apr 2013 22:43:51 +0900
From:	Mitsuhiro Tanino <mitsuhiro.tanino.gm@...achi.com>
To:	Ric Mason <ric.masonn@...il.com>
Cc:	Simon Jeons <simon.jeons@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	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

(2013/04/11 22:00), Ric Mason wrote:
> Hi Mitsuhiro,
> On 04/11/2013 08:51 PM, Mitsuhiro Tanino wrote:
>> (2013/04/11 12:53), Simon Jeons wrote:
>>> One question against mce instead of the patchset. ;-)
>>>
>>> When check memory is bad? Before memory access? Is there a process scan it period?
>> Hi Simon-san,
>>
>> Yes, there is a process to scan memory periodically.
>>
>> At Intel Nehalem-EX and CPUs after Nehalem-EX generation, MCA recovery
>> is supported. MCA recovery provides error detection and isolation
>> features to work together with OS.
>> One of the MCA Recovery features is Memory Scrubbing. It periodically
>> checks memory in the background of OS.
> 
> Memory Scrubbing is a kernel thread? Where is the codes of memory scrubbing?

Hi Ric,

No. One of the MCA Recovery features is Memory Scrubbing.
And Memory Scrubbing is a hardware feature of Intel CPU.

OS has a hwpoison feature which is included at mm/memory-failure.c.
A main function is memory_failure().

If Memory Scrubbing finds a memory error, MCA recovery notifies SRAO error
into OS and OS handles the SRAO error using hwpoison function.


>> If Memory Scrubbing find an uncorrectable error on a memory before
>> OS accesses the memory bit, MCA recovery notifies SRAO error into OS
> 
> It maybe can't find memory error timely since it is sleeping when memory error occur, can this case happened?

Memory Scrubbing seems to be operated periodically but I don't have
information about how oftern it is executed.

Regards,
Mitsuhiro Tanino

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