linux-kernel - [PATCH 1/3] mm: page_isolation: remove redundant moving for isolated buddy pages

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Date:	Tue, 09 Dec 2014 15:50:35 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	iamjoonsoo.kim@....com
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>, mgorman@...e.de,
	'Rik van Riel' <riel@...hat.com>, vbabka@...e.cz,
	'Johannes Weiner' <hannes@...xchg.org>,
	'Minchan Kim' <minchan@...nel.org>,
	'Weijie Yang' <weijie.yang.kh@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 1/3] mm: page_isolation: remove redundant moving for isolated
 buddy pages

The commit ad53f92e(fix incorrect isolation behavior by rechecking migratetype)
patch series describe the race between page isolation and alloc/free path, and
fix the race.

Now, after the pageblock has been isolated, free buddy pages are already in
the free_list[MIGRATE_ISOLATE] and will not be allocated for usage. So the
current freepage_migratetype check is unnecessary and it will cause redundant
page move. That is to say, even if the buddy page's migratetype is not
MIGRATE_ISOLATE, the page is in free_list[MIGRATE_ISOLATE], we just move it
from free_list[MIGRATE_ISOLATE] to free_list[MIGRATE_ISOLATE].

This patch removes the unnecessary freepage_migratetype check and the
redundant page moving.

Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
---
 mm/page_isolation.c |   17 +----------------
 1 file changed, 1 insertion(+), 16 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c8778f7..6e5174d 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -221,23 +221,8 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 			continue;
 		}
 		page = pfn_to_page(pfn);
-		if (PageBuddy(page)) {
-			/*
-			 * 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;
-
-				end_page = page + (1 << page_order(page)) - 1;
-				move_freepages(page_zone(page), page, end_page,
-						MIGRATE_ISOLATE);
-			}
+		if (PageBuddy(page))
 			pfn += 1 << page_order(page);
-		}
 		else if (page_count(page) == 0 &&
 			get_freepage_migratetype(page) == MIGRATE_ISOLATE)
 			pfn += 1;
-- 
1.7.10.4


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