linux-kernel - [PATCH 2/7] mm/balloon_compaction: keep ballooned pages away from normal migration path

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Date:	Wed, 20 Aug 2014 19:04:40 +0400
From:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>
To:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Rafael Aquini <aquini@...hat.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] mm/balloon_compaction: keep ballooned pages away from
 normal migration path

Proper testing shows yet another problem in balloon migration: it works only
once for each page. balloon_page_movable() check page flags and page_count.
In __unmap_and_move page is locked, reference counter is elevated, so
balloon_page_movable() _always_ fails here. As result in __unmap_and_move()
migration goes to the normal migration path.

Balloon ->migratepage() is so special, it returns MIGRATEPAGE_BALLOON_SUCCESS
instead of MIGRATEPAGE_SUCCESS. After that in move_to_new_page() successfully
migrated page got NULL into its mapping pointer and loses connectivity with
balloon and ability for further migration.

It's safe to use __is_movable_balloon_page here: page is isolated and pinned.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@...sung.com>
Cc: stable <stable@...r.kernel.org> # v3.8
---
 mm/migrate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index f78ec9b..161d044 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -873,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 		}
 	}

-	if (unlikely(balloon_page_movable(page))) {
+	if (unlikely(__is_movable_balloon_page(page))) {
 		/*
 		 * A ballooned page does not need any special attention from
 		 * physical to virtual reverse mapping procedures.

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