linux-kernel - [PATCH] mm: reset migratetype if the range spans two pageblocks

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Date:	Fri, 16 Oct 2015 18:06:46 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
	<mhocko@...e.com>, <js1304@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	<alexander.h.duyck@...hat.com>, <zhongjiang@...wei.com>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] mm: reset migratetype if the range spans two pageblocks

__rmqueue_fallback() will change the migratetype of pageblock,
so it is possible that two continuous pageblocks have different
migratetypes.

When freeing all pages of the two blocks, they will be merged
to 4M, and added to the buddy list which the migratetype is the
first pageblock's.

If later alloc some pages and split the 4M, the second pageblock
will be added to the buddy list, and the migratetype is the first
pageblock's, so it is different from the its pageblock's.

That means the page in buddy list's migratetype is different from
the page in pageblock's migratetype. This will make confusion.

However,if we change the hotpath, it will be performance degradation,
so any better ideas?

Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 48aaf7b..5c91348 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -726,6 +726,9 @@ static inline void __free_one_page(struct page *page,
 	list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
 out:
 	zone->free_area[order].nr_free++;
+	/* If the range spans two pageblocks, reset the migratetype. */
+	if (order > pageblock_order)
+		change_pageblock_range(page, order, migratetype);
 }

 static inline int free_pages_check(struct page *page)
-- 
2.0.0

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