linux-kernel - Re: CMA and zone watermarks

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Date:	Tue, 09 Oct 2012 05:12:21 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Rabin Vincent <rabin@....in>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: CMA and zone watermarks

Hello,

On 10/9/2012 5:10 AM, Minchan Kim wrote:

> On Mon, Oct 08, 2012 at 05:41:14PM +0200, Rabin Vincent wrote:
>> It appears that when CMA is enabled, the zone watermarks are not properly
>> respected, leading to for example GFP_NOWAIT allocations getting access to the
>> high pools.
>>
>> I ran the following test code which simply allocates pages with GFP_NOWAIT
>> until it fails, and then tries GFP_ATOMIC.  Without CMA, the GFP_ATOMIC
>> allocation succeeds, with CMA, it fails too.
>
> Good spot. By wrong zone_watermark_check, it can consume reserved memory pool.

That was the main reason for the Bartek's research.

>> Logs attached (includes my patch which prints the migration type in the failure
>> message http://marc.info/?l=linux-mm&m=134971041701306&w=2), taken on 3.6
>> kernel.
>>
>
> Fortunately, recently, Bart sent a patch about that.
> http://marc.info/?l=linux-mm&m=134763299016693&w=2
>
> Could you test above patches in your kernel?
> You have to apply [2/4], [3/4], [4/4] and don't need [1/4].

AFAIR without patch [1/4], free cma page counter will go below zero and 
weird thing will happen, so better apply the complete patchset.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center
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