linux-kernel - Re: [PATCH 04/11] Allow CONFIG_MIGRATION to be set without CONFIG

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Message-ID: <20100319101651.GT12388@csn.ul.ie>
Date:	Fri, 19 Mar 2010 10:16:51 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 04/11] Allow CONFIG_MIGRATION to be set without
	CONFIG_NUMA or memory hot-remove

On Fri, Mar 19, 2010 at 03:21:20PM +0900, KOSAKI Motohiro wrote:
> > On Thu, Mar 18, 2010 at 08:56:23AM +0900, KOSAKI Motohiro wrote:
> > > > On Wed, 17 Mar 2010, Mel Gorman wrote:
> > > > 
> > > > > > If select MIGRATION works, we can remove "depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE"
> > > > > > line from config MIGRATION.
> > > > > >
> > > > >
> > > > > I'm not quite getting why this would be an advantage. COMPACTION
> > > > > requires MIGRATION but conceivable both NUMA and HOTREMOVE can work
> > > > > without it.
> > > > 
> > > > Avoids having to add additional CONFIG_XXX on the page migration "depends"
> > > > line in the future.
> > > 
> > > Yes, Kconfig mess freqently shot ourself in past days. if we have a chance
> > > to remove unnecessary dependency, we should do. that's my intention of the last mail.
> > > 
> > 
> > But if the depends line is removed, it could be set without NUMA, memory
> > hot-remove or compaction enabled. That wouldn't be very useful. I'm
> > missing something obvious.
> 
> Perhaps I'm missing something. 
> 
> my point is, force enabling useless config is not good idea (yes, i agree). but config 
> selectability doesn't cause any failure. IOW, usefulness and dependency aren't 
> related so much. personally I dislike _unnecessary_ dependency.
> 
> If my opinion cause any bad thing, I'll withdraw it. of course.
> 

I've changed the MIGRATION entry to

config MIGRATION
        bool "Page migration"
        def_bool y
        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE 

i.e. it no longer depends on COMPACTION because the "select MIGRATION"
in that line is enough.

I've left NUMA and HOTREMOVE because migration is an optional feature
for those configurations.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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