linux-kernel - [PATCH 2/2] Align ZONE_MOVABLE to a MAX_ORDER_NR

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Message-Id: <20070424180112.22005.34624.sendpatchset@skynet.skynet.ie>
Date:	Tue, 24 Apr 2007 19:01:12 +0100 (IST)
From:	Mel Gorman <mel@....ul.ie>
To:	akpm@...ux-foundation.org
Cc:	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, apw@...dowen.org, y-goto@...fujitsu.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: [PATCH 2/2] Align ZONE_MOVABLE to a MAX_ORDER_NR_PAGES boundary

The boot memory allocator makes assumptions on the alignment of zone
boundaries even though the buddy allocator has no requirements on the
alignment of zones. This may cause boot problems in situations where
ZONE_MOVABLE is populated because the bootmem allocator assumes zones are
at least order-log2(BITS_PER_LONG) aligned. As the two potential users
(huge pages and memory hot-remove) of ZONE_MOVABLE would prefer a higher
alignment, this patch aligns the start of the zone instead of fixing the
different assumptions made by the bootmem allocator.

This patch rounds the start of ZONE_MOVABLE in each node to a
MAX_ORDER_NR_PAGES boundary. If the rounding pushes the start of ZONE_MOVABLE
above the end of the node then the zone will contain no memory and will not
be used at runtime. The value is rounded up instead of down as it is
better to have the kernel-portion of memory larger than requested instead
of smaller. The impact is that the kernel-usable portion of memory because a
minimum guarantee instead of the exact size requested by the user.

Signed-off-by: Mel Gorman <mel@....ul.ie>
Acked-by: Andy Whitcroft <apw@...dowen.org>
---

 page_alloc.c |    5 +++++
 1 files changed, 5 insertions(+)

diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.21-rc6-mm1-002_commonparse/mm/page_alloc.c linux-2.6.21-rc6-mm1-003_alignmovable/mm/page_alloc.c
--- linux-2.6.21-rc6-mm1-002_commonparse/mm/page_alloc.c	2007-04-24 09:38:30.000000000 +0100
+++ linux-2.6.21-rc6-mm1-003_alignmovable/mm/page_alloc.c	2007-04-24 11:15:40.000000000 +0100
@@ -3642,6 +3642,11 @@ restart:
 	usable_nodes--;
 	if (usable_nodes && required_kernelcore > usable_nodes)
 		goto restart;
+	
+	/* Align start of ZONE_MOVABLE on all nids to MAX_ORDER_NR_PAGES */
+	for (nid = 0; nid < MAX_NUMNODES; nid++)
+		zone_movable_pfn[nid] =
+			roundup(zone_movable_pfn[nid], MAX_ORDER_NR_PAGES);
 }

 /**
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