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Date: Thu, 28 Aug 2014 19:35:00 +0100
From: Mel Gorman <mgorman@...e.de>
To: Jiri Slaby <jslaby@...e.cz>
Cc: Linux-Stable <stable@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 52/97] mm/compaction: cleanup isolate_freepages()
From: Vlastimil Babka <vbabka@...e.cz>
commit c96b9e508f3d06ddb601dcc9792d62c044ab359e upstream.
isolate_freepages() is currently somewhat hard to follow thanks to many
looks like it is related to the 'low_pfn' variable, but in fact it is not.
This patch renames the 'high_pfn' variable to a hopefully less confusing name,
and slightly changes its handling without a functional change. A comment made
obsolete by recent changes is also updated.
[akpm@...ux-foundation.org: comment fixes, per Minchan]
[iamjoonsoo.kim@....com: cleanups]
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc: Michal Nazarewicz <mina86@...a86.com>
Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Dongjun Shin <d.j.shin@...sung.com>
Cc: Sunghwan Yun <sunghwan.yun@...sung.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
mm/compaction.c | 56 +++++++++++++++++++++++++++-----------------------------
1 file changed, 27 insertions(+), 29 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index c5f2f18..43d37cd 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -663,7 +663,10 @@ static void isolate_freepages(struct zone *zone,
struct compact_control *cc)
{
struct page *page;
- unsigned long high_pfn, low_pfn, pfn, z_end_pfn;
+ unsigned long block_start_pfn; /* start of current pageblock */
+ unsigned long block_end_pfn; /* end of current pageblock */
+ unsigned long low_pfn; /* lowest pfn scanner is able to scan */
+ unsigned long next_free_pfn; /* start pfn for scaning at next round */
int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;
@@ -671,32 +674,33 @@ static void isolate_freepages(struct zone *zone,
* Initialise the free scanner. The starting point is where we last
* 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 pageblock boundary, because we do
+ * block_start_pfn -= pageblock_nr_pages in the for loop.
+ * For ending point, take care when isolating in last pageblock of a
+ * a zone which ends in the middle of a pageblock.
* The low boundary is the end of the pageblock the migration scanner
* is using.
*/
- pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
+ block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
+ block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
+ zone_end_pfn(zone));
low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
/*
- * Take care that if the migration scanner is at the end of the zone
- * that the free scanner does not accidentally move to the next zone
- * in the next isolation cycle.
+ * If no pages are isolated, the block_start_pfn < low_pfn check
+ * will kick in.
*/
- high_pfn = min(low_pfn, pfn);
-
- z_end_pfn = zone_end_pfn(zone);
+ next_free_pfn = 0;
/*
* Isolate free pages until enough are available to migrate the
* pages on cc->migratepages. We stop searching if the migrate
* and free page scanners meet or enough free pages are isolated.
*/
- for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
- pfn -= pageblock_nr_pages) {
+ for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
+ block_end_pfn = block_start_pfn,
+ block_start_pfn -= pageblock_nr_pages) {
unsigned long isolated;
- unsigned long end_pfn;
/*
* This can iterate a massively long zone without finding any
@@ -705,7 +709,7 @@ static void isolate_freepages(struct zone *zone,
*/
cond_resched();
- if (!pfn_valid(pfn))
+ if (!pfn_valid(block_start_pfn))
continue;
/*
@@ -715,7 +719,7 @@ static void isolate_freepages(struct zone *zone,
* i.e. it's possible that all pages within a zones range of
* pages do not belong to a single zone.
*/
- page = pfn_to_page(pfn);
+ page = pfn_to_page(block_start_pfn);
if (page_zone(page) != zone)
continue;
@@ -728,14 +732,8 @@ static void isolate_freepages(struct zone *zone,
continue;
/* Found a block suitable for isolating free pages from */
-
- /*
- * Take care when isolating in last pageblock of a zone which
- * ends in the middle of a pageblock.
- */
- end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);
- isolated = isolate_freepages_block(cc, pfn, end_pfn,
- freelist, false);
+ isolated = isolate_freepages_block(cc, block_start_pfn,
+ block_end_pfn, freelist, false);
nr_freepages += isolated;
/*
@@ -743,9 +741,9 @@ static void isolate_freepages(struct zone *zone,
* looking for free pages, the search will restart here as
* page migration may have returned some pages to the allocator
*/
- if (isolated) {
+ if (isolated && next_free_pfn == 0) {
cc->finished_update_free = true;
- high_pfn = max(high_pfn, pfn);
+ next_free_pfn = block_start_pfn;
}
}
@@ -756,10 +754,10 @@ static void isolate_freepages(struct zone *zone,
* If we crossed the migrate scanner, we want to keep it that way
* so that compact_finished() may detect this
*/
- if (pfn < low_pfn)
- cc->free_pfn = max(pfn, zone->zone_start_pfn);
- else
- cc->free_pfn = high_pfn;
+ if (block_start_pfn < low_pfn)
+ next_free_pfn = cc->migrate_pfn;
+
+ cc->free_pfn = next_free_pfn;
cc->nr_freepages = nr_freepages;
}
--
1.8.4.5
--
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