mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaim

Lumpy reclaim is disruptive.  It reclaims a large number of pages and
ignores the age of the pages it reclaims.  This can incur significant
stalls and potentially increase the number of major faults.

Compaction has reached the point where it is considered reasonably stable
(meaning it has passed a lot of testing) and is a potential candidate for
displacing lumpy reclaim.  This patch introduces an alternative to lumpy
reclaim whe compaction is available called reclaim/compaction.  The basic
operation is very simple - instead of selecting a contiguous range of
pages to reclaim, a number of order-0 pages are reclaimed and then
compaction is later by either kswapd (compact_zone_order()) or direct
compaction (__alloc_pages_direct_compact()).

[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: use conventional task_struct naming]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index 5ac51552d908..2592883d862d 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -22,6 +22,9 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
 extern int fragmentation_index(struct zone *zone, unsigned int order);
 extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
                         int order, gfp_t gfp_mask, nodemask_t *mask);
+extern unsigned long compaction_suitable(struct zone *zone, int order);
+extern unsigned long compact_zone_order(struct zone *zone, int order,
+                                                gfp_t gfp_mask);
 
 /* Do not skip compaction more than 64 times */
 #define COMPACT_MAX_DEFER_SHIFT 6
@@ -59,6 +62,17 @@ static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
         return COMPACT_CONTINUE;
 }
 
+static inline unsigned long compaction_suitable(struct zone *zone, int order)
+{
+        return COMPACT_SKIPPED;
+}
+
+static inline unsigned long compact_zone_order(struct zone *zone, int order,
+                                                gfp_t gfp_mask)
+{
+        return 0;
+}
+
 static inline void defer_compaction(struct zone *zone)
 {
 }