linux-kernel - [PATCH 3/3] mm: page_alloc: remove redundant set_freepage

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Message-id: <000301d01385$45554a60$cfffdf20$%yang@samsung.com>
Date:	Tue, 09 Dec 2014 15:51:49 +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 3/3] mm: page_alloc: remove redundant
 set_freepage_migratetype() calls

The freepage_migratetype is a temporary cached value which represents
the free page's pageblock migratetype. Now we use it in two scenarios:

1. Use it as a cached value in page freeing path. This cached value
is temporary and non-100% update, which help us decide which pcp
freelist and buddy freelist the page should go rather than using
get_pfnblock_migratetype() to save some instructions.
When there is race between page isolation and free path, we need use
additional method to get a accurate value to put the free pages to
the correct freelist and get a precise free pages statistics.

2. Use it in page alloc path to update NR_FREE_CMA_PAGES statistics.

This patch aims at the scenario 1 and removes two redundant
set_freepage_migratetype() calls, which will make sense in the hot path.

Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
---
 mm/page_alloc.c |    2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 616a2c9..99af01a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -775,7 +775,6 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	migratetype = get_pfnblock_migratetype(page, pfn);
 	local_irq_save(flags);
 	__count_vm_events(PGFREE, 1 << order);
-	set_freepage_migratetype(page, migratetype);
 	free_one_page(page_zone(page), page, pfn, order, migratetype);
 	local_irq_restore(flags);
 }
@@ -1024,7 +1023,6 @@ int move_freepages(struct zone *zone,
 		order = page_order(page);
 		list_move(&page->lru,
 			  &zone->free_area[order].free_list[migratetype]);
-		set_freepage_migratetype(page, migratetype);
 		page += 1 << order;
 		pages_moved += 1 << order;
 	}
-- 
1.7.10.4

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