From: Arnd Bergmann <arnd@arndb.de>
To: "Michal Nazarewicz" <mina86@mina86.com>
Subject: Re: [PATCH 08/10] mm: cma: Contiguous Memory Allocator added
Date: Tue, 14 Jun 2011 20:30:07 +0200
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Cc: "Marek Szyprowski" <m.szyprowski@samsung.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-media@vger.kernel.org, linux-mm@kvack.org,
        linaro-mm-sig@lists.linaro.org,
        "'Kyungmin Park'" <kyungmin.park@samsung.com>,
        "'Andrew Morton'" <akpm@linux-foundation.org>,
        "'KAMEZAWA Hiroyuki'" <kamezawa.hiroyu@jp.fujitsu.com>,
        "'Ankita Garg'" <ankita@in.ibm.com>,
        "'Daniel Walker'" <dwalker@codeaurora.org>,
        "'Mel Gorman'" <mel@csn.ul.ie>,
        "'Jesse Barker'" <jesse.barker@linaro.org>
References: <1307699698-29369-1-git-send-email-m.szyprowski@samsung.com> <201106141803.00876.arnd@arndb.de> <op.vw2r3xrj3l0zgt@mnazarewicz-glaptop>
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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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