linux-kernel - Re: [Linaro-mm-sig] [PATCH 02/10] lib: genalloc: Generic allocator improvements

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Date:	Tue, 14 Jun 2011 09:49:05 -0600
From:	Jordan Crouse <jcrouse@...eaurora.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Marek Szyprowski <m.szyprowski@...sung.com>,
	'Ankita Garg' <ankita@...ibm.com>,
	'Daniel Walker' <dwalker@...eaurora.org>,
	'Arnd Bergmann' <arnd@...db.de>,
	'Johan MOSSBERG' <johan.xx.mossberg@...ricsson.com>,
	'Jesse Barker' <jesse.barker@...aro.org>,
	'Mel Gorman' <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	'Michal Nazarewicz' <mina86@...a86.com>,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	'Kyungmin Park' <kyungmin.park@...sung.com>,
	'KAMEZAWA Hiroyuki' <kamezawa.hiroyu@...fujitsu.com>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [Linaro-mm-sig] [PATCH 02/10] lib: genalloc: Generic allocator
 improvements

On 06/10/2011 06:52 AM, Alan Cox wrote:
>> I plan to replace it with lib/bitmap.c bitmap_* based allocator (similar like
>> it it is used by dma_declare_coherent_memory() and friends in
>> drivers/base/dma-coherent.c). We need something really simple for CMA area
>> management.
>>
>> IMHO allocate_resource and friends a bit too heavy here, but good to know
>> that such allocator also exists.
>
> Not sure I'd class allocate_resource as heavyweight but providing it's
> using something that already exists rather than inventing yet another
> allocator.
>
> This wants dealing with before it goes upstream though so the chaneges in
> lib/*c etc never have to reach mainline and then get changed back.

Even if CMA doesn't end up using genalloc, there are existing consumers of
the API and I think the _aligned function has value.

I agree that allocate_resource isn't overly heavy, but comparatively genalloc
is really simple and lightweight for a driver to manage a contiguous address
space without a lot of extra thought. I think both APIs serve slightly
different masters, but if somebody thought about it long enough there could
be some consolidation (same goes for the internal guts of
dma_declare_coherent_memory).

I agree with Michal - if genalloc goes deprecated, then so be it, but as
long as it lives, I think its useful to get these functions upstream.

Jordan
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