linux-kernel - Re: [PATCH 08/10] mm: cma: Contiguous Memory Allocator added

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Message-Id: <201106142030.07549.arnd@arndb.de>
Date:	Tue, 14 Jun 2011 20:30:07 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michal Nazarewicz" <mina86@...a86.com>
Cc:	"Marek Szyprowski" <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org,
	"'Kyungmin Park'" <kyungmin.park@...sung.com>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'KAMEZAWA Hiroyuki'" <kamezawa.hiroyu@...fujitsu.com>,
	"'Ankita Garg'" <ankita@...ibm.com>,
	"'Daniel Walker'" <dwalker@...eaurora.org>,
	"'Mel Gorman'" <mel@....ul.ie>,
	"'Jesse Barker'" <jesse.barker@...aro.org>
Subject: Re: [PATCH 08/10] mm: cma: Contiguous Memory Allocator added

On Tuesday 14 June 2011 18:58:35 Michal Nazarewicz wrote:
> On Tue, 14 Jun 2011 18:03:00 +0200, Arnd Bergmann wrote:
> > For all I know, that is something that is only true for a few very  
> > special Samsung devices,
> 
> Maybe.  I'm just answering your question. :)
> 
> Ah yes, I forgot that separate regions for different purposes could
> decrease fragmentation.

That is indeed a good point, but having a good allocator algorithm
could also solve this. I don't know too much about these allocation
algorithms, but there are probably multiple working approaches to this.

> > I would suggest going forward without having multiple regions:
> 
> Is having support for multiple regions a bad thing?  Frankly,
> removing this support will change code from reading context passed
> as argument to code reading context from global variable.  Nothing
> is gained; functionality is lost.

What is bad IMHO is making them the default, which forces the board
code to care about memory management details. I would much prefer
to have contiguous allocation parameters tuned automatically to just
work on most boards before we add ways to do board-specific hacks.

	Arnd
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