linux-kernel - [PATCH] memory hotplug: fix alignment check (Was Re: PROBLEM: __offline_isolated

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Message-Id: <20101217085714.5525793b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 17 Dec 2010 08:57:14 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Ingo Korb <ingo@...na.de>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, cl@...ux-foundation.org,
	yinghai@...nel.org, andi.kleen@...el.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH] memory hotplug: fix alignment check (Was Re: PROBLEM:
 __offline_isolated_pages may offline too many pages

On Thu, 16 Dec 2010 10:26:41 +0000
Mel Gorman <mel@....ul.ie> wrote:

> Other than the spelling mistakes in the changelog and the lack of a
> subject;
> 
> Acked-by: Mel Gorman <mel@....ul.ie>
> 
Thank you. fixed one.
==

offline_pages()'s sanity check of given range is wrong. It should
be aligned to MAX_ORDER. Current existing caller uses SECTION_SIZE
alignment, so this change has no influence to existing callers.

Reported-by: Ingo Korb <ingo@...na.de>
Acked-by: Mel Gorman <mel@....ul.ie>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/memory_hotplug.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Index: linux-2.6.37-rc5/mm/memory_hotplug.c
===================================================================
--- linux-2.6.37-rc5.orig/mm/memory_hotplug.c
+++ linux-2.6.37-rc5/mm/memory_hotplug.c
@@ -798,10 +798,14 @@ static int offline_pages(unsigned long s
 	struct memory_notify arg;
 
 	BUG_ON(start_pfn >= end_pfn);
-	/* at least, alignment against pageblock is necessary */
-	if (!IS_ALIGNED(start_pfn, pageblock_nr_pages))
+	/*
+	 * Considering Buddy system which joins nearby pages, the range
+	 * in offline should be aligned to MAX_ORDER. If not, isolated
+	 * page will be joined to other (not isolated) pages.
+	 */
+	if (!IS_ALIGNED(start_pfn, MAX_ORDER_NR_PAGES))
 		return -EINVAL;
-	if (!IS_ALIGNED(end_pfn, pageblock_nr_pages))
+	if (!IS_ALIGNED(end_pfn, MAX_ORDER_NR_PAGES))
 		return -EINVAL;
 	/* This makes hotplug much easier...and readable.
 	   we assume this for now. .*/
 

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