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

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Message-Id: <20100827171639.83c8642c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 27 Aug 2010 17:16:39 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Michał Nazarewicz <m.nazarewicz@...sung.com>,
	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 18:36:24 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> On Thu, Aug 26, 2010 at 1:30 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > On Thu, 26 Aug 2010 13:06:28 +0900
> > Minchan Kim <minchan.kim@...il.com> wrote:
> >
> >> On Thu, Aug 26, 2010 at 12:44 PM, KAMEZAWA Hiroyuki
> >> <kamezawa.hiroyu@...fujitsu.com> wrote:
> >> > On Thu, 26 Aug 2010 11:50:17 +0900
> >> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> >> >
> >> >> 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.
> >> >>
> >> > Ah, I need to clarify what I want to say.
> >> >
> >> > With compaction, it's helpful, but you can't get contiguous memory larger
> >> > than MAX_ORDER, I think. To get memory larger than MAX_ORDER on demand,
> >> > memory hot-plug code has almost all necessary things.
> >>
> >> True. Doesn't patch's idea of Christoph helps this ?
> >> http://lwn.net/Articles/200699/
> >>
> >
> > yes, I think so. But, IIRC,  it's own purpose of Chirstoph's work is
> > for removing zones. please be careful what's really necessary.
> 
> Ahh. Sorry for missing point.
> You're right. The patch can't help our problem.
> 
> How about changing following this?
> The thing is MAX_ORDER is static. But we want to avoid too big
> MAX_ORDER of whole zones to support devices which requires big
> allocation chunk.
> So let's add MAX_ORDER into each zone and then, each zone can have
> different max order.
> For example, while DMA[32], NORMAL, HIGHMEM can have normal size 11,
> MOVABLE zone could have a 15.
> 
> This approach has a big side effect?
> 

Hm...need to check hard coded MAX_ORDER usages...I don't think
side-effect is big. Hmm. But I think enlarging MAX_ORDER isn't an
important thing. A code which strips contiguous chunks of pages from
buddy allocator is a necessaty thing, as..

What I can think of at 1st is...
==
	int steal_pages(unsigned long start_pfn, unsigned long end_pfn)
	{
		/* Be careful mutal execution with memory hotplug, because reusing code */

		split [start_pfn, end_pfn) to pageblock_order
		
		for each pageblock in the range {
			Mark this block as MIGRATE_ISOLATE
			try-to-free pages in the range or
			migrate pages in the range to somewhere.
			/* Here all pages in the range are on buddy allocator
			and free and never be allocated by anyone else. */
		}

		please see __rmqueue_fallback(). it selects migration-type at 1st.
		Then, if you can pass start_migratetype of MIGLATE_ISOLATE,
		you can automatically strip all MIGRATE_ISOLATE pages from free_area[].

		return chunk of pages.
	}
==

Thanks,
-Kame



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