linux-kernel - Re: [RFC][PATCH] CMA: drivers/base/Kconfig: restrict CMA size to non-zero value

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Date:	Tue, 20 May 2014 11:26:55 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Michal Nazarewicz <mina86@...a86.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Minchan Kim <minchan.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Laura Abbott <lauraa@...eaurora.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Heesub Shin <heesub.shin@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	이건호 <gunho.lee@....com>, gurugio@...il.com
Subject: Re: [RFC][PATCH] CMA: drivers/base/Kconfig: restrict CMA size to
 non-zero value


2014-05-20 오전 10:28, Michal Nazarewicz 쓴 글:
> On Mon, May 19 2014, Gioh Kim wrote:
>> If CMA option is not selected, __alloc_from_contiguous would not be
>> called.  We don't need to the fallback allocation.
>>
>> And if CMA option is selected and initialized correctly,
>> the cma allocation can fail in case of no-CMA-memory situation.
>> I thinks in that case we don't need to the fallback allocation also,
>> because it is normal case.
>>
>> Therefore I think the restriction of CMA size option and make CMA work
>> can cover every cases.
>
> Wait, you just wrote that if CMA is not initialised correctly, it's fine
> for atomic pool initialisation to fail, but if CMA size is initialised
> correctly but too small, this is somehow worse situation?  I'm a bit
> confused to be honest.

I'm sorry to confuse you.
Please forgive my poor English.
My point is atomic_pool should be able to work with/without CMA.


>
> IMO, cma=0 command line argument should be supported, as should having
> the default CMA size zero.  If CMA size is set to zero, kernel should
> behave as if CMA was not enabled at compile time.

It's also good if atomic_pool can work well with zero CMA size.

I can give up my patch.
But Joonsoo's patch should be applied.

Joonsoo, can you please send the full patch to maintainers?

>
>
>
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