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

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Message-ID: <AANLkTikS9Bc1NmCCO5w=pT+LBLaeSyk2PBnAry+oDxM8@mail.gmail.com>
Date:	Thu, 26 Aug 2010 19:21:55 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <m.nazarewicz@...sung.com>,
	linux-mm@...ck.org, Daniel Walker <dwalker@...eaurora.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Hans Verkuil <hverkuil@...all.nl>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Pawel Osciak <p.osciak@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Zach Pfeffer <zpfeffer@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

On Thu, Aug 26, 2010 at 7:06 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2010-08-26 at 18:29 +0900, Minchan Kim wrote:
>> As I said following mail, I said about free space problem.
>> Of course, compaction could move anon pages into somewhere.
>> What's is somewhere? At last, it's same zone.
>> It can prevent fragment problem but not size of free space.
>> So I mean it would be better to move it into another zone(ex, HIGHMEM)
>> rather than OOM kill.
>
> Real machines don't have highmem, highmem sucks!! /me runs

It's another topic.
I agree highmem isn't a gorgeous. But my desktop isn't real machine?
Important thing is that we already have a highmem and many guys
include you(kmap stacking patch :))try to improve highmem problems. :)

>
> Does cross zone movement really matter, I though these crappy devices
> were mostly used on crappy hardware with very limited memory, so pretty
> much everything would be in zone_normal.. no?

No. Until now, many embedded devices have used to small memory. In
that case, only there is a DMA zone in system. But as I know, mobile
phone starts to use big(?) memory like 1G or above sooner or later. So
they starts to use HIGHMEM. Otherwise, 2G/2G space configuration.
Some embedded device uses many thread model to port easily from RTOS.
In that case, they don't have enough address space for application if
it uses 2G/2G model.

So we should care of HIGHMEM in embedded system from now on.

>
> But sure, if there's really a need we can look at maybe doing cross zone
> movement.
>


-- 
Kind regards,
Minchan Kim
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