[PATCH] Fix page_group_by_mobility_disabled breakage

[PATCH] Fix page_group_by_mobility_disabled breakage

[kosaki.motohiro]

From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Currently, set_pageblock_migratetype screw up MIGRATE_CMA and
MIGRATE_ISOLATE if page_group_by_mobility_disabled is true. It
rewrite the argument to MIGRATE_UNMOVABLE and we lost these attribute.

The problem was introduced commit 49255c619f (page allocator: move
check for disabled anti-fragmentation out of fastpath). So, 4 years
lived issue may mean that nobody uses page_group_by_mobility_disabled.

But anyway, this patch fixes the problem.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
---
 mm/page_alloc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dd886fa..ef44d95 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -234,8 +234,8 @@ int page_group_by_mobility_disabled __read_mostly;
 
 void set_pageblock_migratetype(struct page *page, int migratetype)
 {
-
-	if (unlikely(page_group_by_mobility_disabled))
+	if (unlikely(page_group_by_mobility_disabled &&
+		     migratetype < MIGRATE_PCPTYPES))
 		migratetype = MIGRATE_UNMOVABLE;
 
 	set_pageblock_flags_group(page, (unsigned long)migratetype,
-- 
1.7.1

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Re: [PATCH] Fix page_group_by_mobility_disabled breakage

[Mel Gorman]

On Fri, Oct 25, 2013 at 02:09:35PM -0400, kosaki.motohiro@gmail.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> Currently, set_pageblock_migratetype screw up MIGRATE_CMA and
> MIGRATE_ISOLATE if page_group_by_mobility_disabled is true. It
> rewrite the argument to MIGRATE_UNMOVABLE and we lost these attribute.
> 
> The problem was introduced commit 49255c619f (page allocator: move
> check for disabled anti-fragmentation out of fastpath). So, 4 years
> lived issue may mean that nobody uses page_group_by_mobility_disabled.
> 

Nobody uses page_group_by_mobility_disabled with CMA at least.
page_group_by_mobility_disabled only kicks in automatically for small
machines so it's possible the condition is very rarely encountered.

Anyway

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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