[PATCH 2/2] mm/compaction: cleanup isolate_freepages()

Vlastimil Babka
2014-04-15T09:18:56Z

isolate_freepages() is currently somewhat hard to follow thanks to many
different pfn variables. Especially misleading is the name 'high_pfn' which
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.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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 | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 627dc2e..169c7b2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -671,7 +671,7 @@ 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 pfn, low_pfn, next_free_pfn, z_end_pfn;
int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;

@@ -688,11 +688,10 @@ static void isolate_freepages(struct zone *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.
+ * Seed the value for max(next_free_pfn, pfn) updates. If there are
+ * none, the pfn < low_pfn check will kick in.
*/
- high_pfn = min(low_pfn, pfn);
+ next_free_pfn = 0;

z_end_pfn = zone_end_pfn(zone);

@@ -754,7 +753,7 @@ static void isolate_freepages(struct zone *zone,
*/
if (isolated) {
cc->finished_update_free = true;
- high_pfn = max(high_pfn, pfn);
+ next_free_pfn = max(next_free_pfn, pfn);
}
}

@@ -766,9 +765,9 @@ static void isolate_freepages(struct zone *zone,
* 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;
+ next_free_pfn = max(pfn, zone->zone_start_pfn);
+
+ cc->free_pfn = next_free_pfn;
cc->nr_freepages = nr_freepages;
}

--
1.8.4.5