linux-kernel - Re: [PATCH 0/4] enable migration of driver pages

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Message-ID: <20150729121614.GA19352@techsingularity.net>
Date:	Wed, 29 Jul 2015 13:16:14 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Gioh Kim <gioh.kim@....com>, 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, dri-devel@...ts.freedesktop.org,
	akpm@...ux-foundation.org, Gioh Kim <gurugio@...mail.net>
Subject: Re: [PATCH 0/4] enable migration of driver pages

On Wed, Jul 29, 2015 at 12:55:54PM +0200, Daniel Vetter wrote:
> On Wed, Jul 29, 2015 at 11:49:45AM +0100, Mel Gorman wrote:
> > On Mon, Jul 13, 2015 at 05:35:15PM +0900, Gioh Kim wrote:
> > > 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.
> > > 
> > 
> > The primary motivation of this series is to reduce fragmentation by allowing
> > more kernel pages to be moved. Conceptually that is a worthwhile goal but
> > there should be at least one major in-kernel user and while balloon
> > pages were a good starting point, I think we really need to see what the
> > zram changes look like at the same time.
> 
> I think gpu drivers really would be the perfect candidate for compacting
> kernel page allocations. And this also seems the primary motivation for
> this patch series, so I think that's really what we should use to judge
> these patches.
> 
> Of course then there's the seemingly eternal chicken/egg problem of
> upstream gpu drivers for SoCs :(

I recognised that the driver he had modified was not an in-tree user so
it did not really help the review or the design. I did not think it was
very fair to ask that an in-tree GPU driver be converted when it would not
help the embedded platform of interest. Converting zram is both a useful
illustration of the aops requirements and is expected to be beneficial on
the embedded platform. Now, if a GPU driver author was willing to convert
theirs as an example then that would be useful!

-- 
Mel Gorman
SUSE Labs
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