linux-kernel - Re: [PATCH 1/2][v2] mm: add notifier in pageblock isolation for balloon drivers

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Message-Id: <20091008163449.00dce972.akpm@linux-foundation.org>
Date:	Thu, 8 Oct 2009 16:34:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Robert Jennings <rcj@...ux.vnet.ibm.com>
Cc:	Mel Gorman <mel@....ul.ie>, Ingo Molnar <mingo@...e.hu>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Brian King <brking@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linuxppc-dev@...abs.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/2][v2] mm: add notifier in pageblock isolation for
 balloon drivers

On Fri, 2 Oct 2009 13:44:58 -0500
Robert Jennings <rcj@...ux.vnet.ibm.com> wrote:

> Memory balloon drivers can allocate a large amount of memory which
> is not movable but could be freed to accomodate memory hotplug remove.
> 
> Prior to calling the memory hotplug notifier chain the memory in the
> pageblock is isolated.  If the migrate type is not MIGRATE_MOVABLE the
> isolation will not proceed, causing the memory removal for that page
> range to fail.
> 
> Rather than failing pageblock isolation if the the migrateteype is not
> MIGRATE_MOVABLE, this patch checks if all of the pages in the pageblock
> are owned by a registered balloon driver (or other entity) using a
> notifier chain.  If all of the non-movable pages are owned by a balloon,
> they can be freed later through the memory notifier chain and the range
> can still be isolated in set_migratetype_isolate().

The patch looks sane enough to me.

I expect that if the powerpc and s390 guys want to work on CMM over the
next couple of months, they'd like this patch merged into 2.6.32.  It's
a bit larger and more involved than one would like, but I guess we can
do that if suitable people (Mel?  Kamezawa?) have had a close look and
are OK with it.

What do people think?

Has it been carefully compile- and run-time tested with
CONFIG_MEMORY_HOTPLUG_SPARSE=n?

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