linux-kernel - Re: [RFC] CMA page migration failure due to buffers on bh

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Date:	Tue, 01 Jul 2014 10:07:06 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Laura Abbott <lauraa@...eaurora.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>, Mel Gorman <mgorman@...e.de>,
	이건호 <gunho.lee@....com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC] CMA page migration failure due to buffers on bh_lru

Hi,Laura.

I have a question.

Does the __evict_bh_lru() not need bh_lru_lock()?
The get_cpu_var() has already preenpt_disable() and can prevent other thread.
But get_cpu_var cannot prevent IRQ context such like page-fault.
I think if a page-fault occured and a file is read in IRQ context it can change cpu-lru.

Is my concern correct?


2014-06-30 오전 4:49, Laura Abbott 쓴 글:
> (cc-ing Hugh since he had comments on the patch before)
>
> On 6/26/2014 4:23 PM, Gioh Kim wrote:
>>
>>
>> 2014-06-27 오전 12:57, Michal Nazarewicz 쓴 글:
>>> On Tue, Jun 24 2014, Gioh Kim <gioh.kim@....com> wrote:
>>>> Hello,
>>>>
>>>> I am trying to apply CMA feature for my platform.
>>>> My kernel version, 3.10.x, is not allocating memory from CMA area so that I applied
>>>> a Joonsoo Kim's patch (https://lkml.org/lkml/2014/5/28/64).
>>>> Now my platform can use CMA area effectively.
>>>>
>>>> But I have many failures to allocate memory from CMA area.
>>>> I found the same situation to Laura Abbott's patch descrbing,
>>>> https://lkml.org/lkml/2012/8/31/313,
>>>> that releases buffer-heads attached at CPU's LRU list.
>>>>
>>>> If Joonsoo's patch is applied and/or CMA feature is applied more and more,
>>>> buffer-heads problem is going to be serious definitely.
>>>>
>>>> Please look into the Laura's patch again.
>>>> I think it must be applied with Joonsoo's patch.
>>>
>>> Just to make sure I understood you correctly, you're saying Laura's
>>> patch at <https://lkml.org/lkml/2012/8/31/313> fixes your issue?
>>>
>>
>> Yes, it is.
>
> I submitted this before and it was suggested that this was more
> related to filesystems
>
> http://marc.info/?l=linaro-mm-sig&m=137645770708817&w=2
>
> I never saw more discussion and pushed this into the 'CMA hacks' pile.
> So far we've been keeping the patch out of tree and it's useful to know
> that others have found the same problem. I'm willing to resubmit the
> patch for further discussion.
>
> Thanks,
> Laura
>
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