linux-kernel - Re: [PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

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Date:	Thu, 26 Aug 2010 11:50:17 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michał Nazarewicz <m.nazarewicz@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Daniel Walker <dwalker@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Jonathan Corbet <corbet@....net>,
	Peter Zijlstra <peterz@...radead.org>,
	Pawel Osciak <p.osciak@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Zach Pfeffer <zpfeffer@...eaurora.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Mel Gorman <mel@....ul.ie>, linux-media@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

On Thu, 26 Aug 2010 04:12:10 +0200
Michał Nazarewicz <m.nazarewicz@...sung.com> wrote:

> On Thu, 26 Aug 2010 02:58:57 +0200, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > Hmm, you may not like this..but how about following kind of interface ?
> >
> > Now, memoyr hotplug supports following operation to free and _isolate_
> > memory region.
> > 	# echo offline > /sys/devices/system/memory/memoryX/state
> >
> > Then, a region of memory will be isolated. (This succeeds if there are free
> > memory.)
> >
> > Add a new interface.
> >
> > 	% echo offline > /sys/devices/system/memory/memoryX/state
> > 	# extract memory from System RAM and make them invisible from buddy allocator.
> >
> > 	% echo cma > /sys/devices/system/memory/memoryX/state
> > 	# move invisible memory to cma.
> 
> At this point I need to say that I have no experience with hotplug memory but
> I think that for this to make sense the regions of memory would have to be
> smaller.  Unless I'm misunderstanding something, the above would convert
> a region of sizes in order of GiBs to use for CMA.
> 

Now, x86's section size is 
==
#ifdef CONFIG_X86_32
# ifdef CONFIG_X86_PAE
#  define SECTION_SIZE_BITS     29
#  define MAX_PHYSADDR_BITS     36
#  define MAX_PHYSMEM_BITS      36
# else
#  define SECTION_SIZE_BITS     26
#  define MAX_PHYSADDR_BITS     32
#  define MAX_PHYSMEM_BITS      32
# endif
#else /* CONFIG_X86_32 */
# define SECTION_SIZE_BITS      27 /* matt - 128 is convenient right now */
# define MAX_PHYSADDR_BITS      44
# define MAX_PHYSMEM_BITS       46
#endif
==

128MB...too big ? But it's depend on config.

IBM's ppc guys used 16MB section, and recently, a new interface to shrink
the number of /sys files are added, maybe usable.

Something good with this approach will be you can create "cma" memory
before installing driver.

But yes, complicated and need some works.

Bye,
-Kame

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