From: Minchan Kim <minchan@kernel.org>
Date: Thu, 13 Sep 2012 00:59:00 +0000 (+1000)
Subject: memory-hotplug: fix pages missed by race rather than failing
X-Git-Tag: next-20120920~2^2~134
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=af76b7f5a5b3df06ccf80774edda8e1511caef25;p=karo-tx-linux.git

memory-hotplug: fix pages missed by race rather than failing

If race between allocation and isolation in memory-hotplug offline
happens, some pages could be in MIGRATE_MOVABLE of free_list although the
pageblock's migratetype of the page is MIGRATE_ISOLATE.

The race could be detected by get_freepage_migratetype in
__test_page_isolated_in_pageblock.  If it is detected, now EBUSY gets
bubbled all the way up and the hotplug operations fails.

But better idea is instead of returning and failing memory-hotremove, move
the free page to the correct list at the time it is detected.  It could
enhance memory-hotremove operation success ratio although the race is
really rare.

Suggested by Mel Gorman.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 105077aa7685..fca8c0a5c188 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -6,6 +6,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count);
 void set_pageblock_migratetype(struct page *page, int migratetype);
 int move_freepages_block(struct zone *zone, struct page *page,
 				int migratetype);
+int move_freepages(struct zone *zone,
+			  struct page *start_page, struct page *end_page,
+			  int migratetype);
+
 /*
  * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
  * If specified range includes migrate types other than MOVABLE or CMA,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d97ad0e72f26..dffa91eb0425 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -918,7 +918,7 @@ static int fallbacks[MIGRATE_TYPES][4] = {
  * Note that start_page and end_pages are not aligned on a pageblock
  * boundary. If alignment is required, use move_freepages_block()
  */
-static int move_freepages(struct zone *zone,
+int move_freepages(struct zone *zone,
 			  struct page *start_page, struct page *end_page,
 			  int migratetype)
 {
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 7ba740551d8c..a42fa8d49357 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -194,8 +194,19 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
 		}
 		page = pfn_to_page(pfn);
 		if (PageBuddy(page)) {
-			if (get_freepage_migratetype(page) != MIGRATE_ISOLATE)
-				break;
+			/*
+			 * If race between isolatation and allocation happens,
+			 * some free pages could be in MIGRATE_MOVABLE list
+			 * although pageblock's migratation type of the page
+			 * is MIGRATE_ISOLATE. Catch it and move the page into
+			 * MIGRATE_ISOLATE list.
+			 */
+			if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) {
+				struct page *end_page = page +
+						(1 << page_order(page)) - 1;
+				move_freepages(page_zone(page), page, end_page,
+						MIGRATE_ISOLATE);
+			}
 			pfn += 1 << page_order(page);
 		}
 		else if (page_count(page) == 0 &&