linux-kernel - Re: [RFCv3 0/5] enable migration of driver pages

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Date:	Tue, 7 Jul 2015 15:37:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gioh Kim <gioh.kim@....com>
Cc:	jlayton@...chiereds.net, bfields@...ldses.org, vbabka@...e.cz,
	iamjoonsoo.kim@....com, viro@...iv.linux.org.uk, mst@...hat.com,
	koct9i@...il.com, minchan@...nel.org, aquini@...hat.com,
	linux-fsdevel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-mm@...ck.org, gunho.lee@....com,
	Gioh Kim <gurugio@...mail.net>
Subject: Re: [RFCv3 0/5] enable migration of driver pages

On Tue,  7 Jul 2015 13:36:20 +0900 Gioh Kim <gioh.kim@....com> wrote:

> From: Gioh Kim <gurugio@...mail.net>
> 
> Hello,
> 
> This series try to enable migration of non-LRU pages, such as driver's page.
> 
> My ARM-based platform occured severe fragmentation problem after long-term
> (several days) test. Sometimes even order-3 page allocation failed. It has
> memory size 512MB ~ 1024MB. 30% ~ 40% memory is consumed for graphic processing
> and 20~30 memory is reserved for zram.
> 
> I found that many pages of GPU driver and zram are non-movable pages. So I
> reported Minchan Kim, the maintainer of zram, and he made the internal 
> compaction logic of zram. And I made the internal compaction of GPU driver.
> 
> They reduced some fragmentation but they are not enough effective.
> They are activated by its own interface, /sys, so they are not cooperative
> with kernel compaction. If there is too much fragmentation and kernel starts
> to compaction, zram and GPU driver cannot work with the kernel compaction.
>
> ...
>
> This patch set is tested:
> - turn on Ubuntu 14.04 with 1G memory on qemu.
> - do kernel building
> - after several seconds check more than 512MB is used with free command
> - command "balloon 512" in qemu monitor
> - check hundreds MB of pages are migrated

OK, but what happens if the balloon driver is not used to force
compaction?  Does your test machine successfully compact pages on
demand, so those order-3 allocations now succeed?

Why are your changes to the GPU driver not included in this patch series?


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