linux-kernel - [PATCH] mm: Check if any page in a pageblock is reserved before marking it MIGRATE

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Date:	Mon,  5 Apr 2010 20:09:16 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	TAO HU <tghk48@...orola.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"Ye Yuan.Bo-A22116" <yuan-bo.ye@...orola.com>,
	Chang Qing-A21550 <Qing.Chang@...orola.com>,
	linux-arm-kernel@...ts.infradead.org,
	Arve Hjønnevåg <arve@...roid.com>
Subject: [PATCH] mm: Check if any page in a pageblock is reserved before marking it MIGRATE_RESERVE

This fixes a problem where the first pageblock got marked MIGRATE_RESERVE even
though it only had a few free pages. This in turn caused no contiguous memory
to be reserved and frequent kswapd wakeups that emptied the caches to get more
contiguous memory.

Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
---
 mm/page_alloc.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fb7df1d..46ade16 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2860,6 +2860,20 @@ static inline unsigned long wait_table_bits(unsigned long size)
 #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))
 
 /*
+ * Check if a pageblock contains reserved pages
+ */
+static int pageblock_is_reserved(unsigned long start_pfn)
+{
+	unsigned long end_pfn = start_pfn + pageblock_nr_pages;
+	unsigned long pfn;
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn++)
+		if (!pfn_valid_within(pfn) || PageReserved(pfn_to_page(pfn)))
+			return 1;
+	return 0;
+}
+
+/*
  * Mark a number of pageblocks as MIGRATE_RESERVE. The number
  * of blocks reserved is based on min_wmark_pages(zone). The memory within
  * the reserve will tend to store contiguous free pages. Setting min_free_kbytes
@@ -2898,7 +2912,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
 			continue;
 
 		/* Blocks with reserved pages will never free, skip them. */
-		if (PageReserved(page))
+		if (pageblock_is_reserved(pfn))
 			continue;
 
 		block_migratetype = get_pageblock_migratetype(page);
-- 
1.6.5.1

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