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From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
	Heesub Shin <heesub.shin@samsung.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Dongjun Shin <d.j.shin@samsung.com>,
	Sunghwan Yun <sunghwan.yun@samsung.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Michal Nazarewicz <mina86@mina86.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>
Subject: [PATCH 1/2] mm/compaction: make isolate_freepages start at pageblock boundary
Date: Tue, 15 Apr 2014 11:18:26 +0200	[thread overview]
Message-ID: <1397553507-15330-1-git-send-email-vbabka@suse.cz> (raw)
In-Reply-To: <5342BA34.8050006@suse.cz>

The compaction freepage scanner implementation in isolate_freepages() starts
by taking the current cc->free_pfn value as the first pfn. In a for loop, it
scans from this first pfn to the end of the pageblock, and then subtracts
pageblock_nr_pages from the first pfn to obtain the first pfn for the next
for loop iteration.

This means that when cc->free_pfn starts at offset X rather than being aligned
on pageblock boundary, the scanner will start at offset X in all scanned
pageblock, ignoring potentially many free pages. Currently this can happen when
a) zone's end pfn is not pageblock aligned, or
b) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE enabled and
   a hole spanning the beginning of a pageblock

This patch fixes the problem by aligning the initial pfn in isolate_freepages()
to pageblock boundary. This also allows to replace the end-of-pageblock
alignment within the for loop with a simple pageblock_nr_pages increment.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Heesub Shin <heesub.shin@samsung.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
---
 mm/compaction.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 37f9762..627dc2e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -671,16 +671,20 @@ static void isolate_freepages(struct zone *zone,
 				struct compact_control *cc)
 {
 	struct page *page;
-	unsigned long high_pfn, low_pfn, pfn, z_end_pfn, end_pfn;
+	unsigned long high_pfn, low_pfn, pfn, z_end_pfn;
 	int nr_freepages = cc->nr_freepages;
 	struct list_head *freelist = &cc->freepages;
 
 	/*
 	 * Initialise the free scanner. The starting point is where we last
-	 * scanned from (or the end of the zone if starting). The low point
-	 * is the end of the pageblock the migration scanner is using.
+	 * successfully isolated from, zone-cached value, or the end of the
+	 * zone when isolating for the first time. We need this aligned to
+	 * the pageblock boundary, because we do pfn -= pageblock_nr_pages
+	 * in the for loop.
+	 * The low boundary is the end of the pageblock the migration scanner
+	 * is using.
 	 */
-	pfn = cc->free_pfn;
+	pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
 	low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
 
 	/*
@@ -700,6 +704,7 @@ static void isolate_freepages(struct zone *zone,
 	for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
 					pfn -= pageblock_nr_pages) {
 		unsigned long isolated;
+		unsigned long end_pfn;
 
 		/*
 		 * This can iterate a massively long zone without finding any
@@ -734,13 +739,10 @@ static void isolate_freepages(struct zone *zone,
 		isolated = 0;
 
 		/*
-		 * As pfn may not start aligned, pfn+pageblock_nr_page
-		 * may cross a MAX_ORDER_NR_PAGES boundary and miss
-		 * a pfn_valid check. Ensure isolate_freepages_block()
-		 * only scans within a pageblock
+		 * Take care when isolating in last pageblock of a zone which
+		 * ends in the middle of a pageblock.
 		 */
-		end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
-		end_pfn = min(end_pfn, z_end_pfn);
+		end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);
 		isolated = isolate_freepages_block(cc, pfn, end_pfn,
 						   freelist, false);
 		nr_freepages += isolated;
-- 
1.8.4.5

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  reply	other threads:[~2014-04-15  9:18 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-03  8:57 [PATCH 1/2] mm/compaction: clean up unused code lines Heesub Shin
2014-04-03  8:57 ` [PATCH 2/2] mm/compaction: fix to initialize free scanner properly Heesub Shin
2014-04-07 14:46   ` Vlastimil Babka
2014-04-15  9:18     ` Vlastimil Babka [this message]
2014-04-15  9:18       ` [PATCH 2/2] mm/compaction: cleanup isolate_freepages() Vlastimil Babka
2014-04-16  1:53         ` Joonsoo Kim
2014-04-16 15:49         ` Rik van Riel
2014-04-17  0:07         ` Minchan Kim
2014-04-21 19:41           ` Andrew Morton
2014-04-21 21:43             ` Vlastimil Babka
2014-04-21 23:53               ` Minchan Kim
2014-04-22  6:33                 ` Vlastimil Babka
2014-04-22  6:52                   ` Minchan Kim
2014-04-22 13:17                     ` Vlastimil Babka
2014-04-23  2:58                       ` Joonsoo Kim
2014-04-23  7:30                         ` Vlastimil Babka
2014-04-23 13:54                           ` Joonsoo Kim
2014-04-23 14:31                             ` Vlastimil Babka
2014-04-25  8:29                               ` Joonsoo Kim
2014-04-29  8:40                                 ` Vlastimil Babka
2014-05-01  1:58                                 ` Michal Nazarewicz
2014-04-16  1:52       ` [PATCH 1/2] mm/compaction: make isolate_freepages start at pageblock boundary Joonsoo Kim
2014-04-16 15:47       ` Rik van Riel
2014-04-16 23:43       ` Minchan Kim
2014-04-07 14:40 ` [PATCH 1/2] mm/compaction: clean up unused code lines Vlastimil Babka

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