mm: migration: allow migration to operate asynchronously and avoid synchronous compaction in the faster path

Migration synchronously waits for writeback if the initial passes fails.
Callers of memory compaction do not necessarily want this behaviour if the
caller is latency sensitive or expects that synchronous migration is not
going to have a significantly better success rate.

This patch adds a sync parameter to migrate_pages() allowing the caller to
indicate if wait_on_page_writeback() is allowed within migration or not.
For reclaim/compaction, try_to_compact_pages() is first called
asynchronously, direct reclaim runs and then try_to_compact_pages() is
called synchronously as there is a greater expectation that it'll succeed.

[akpm@linux-foundation.org: build/merge fix]
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, 10 insertions, 4 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 8fe917ec7c11..47fca1069343 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -33,6 +33,7 @@ struct compact_control {
         unsigned long nr_migratepages;  /* Number of pages to migrate */
         unsigned long free_pfn;         /* isolate_freepages search base */
         unsigned long migrate_pfn;      /* isolate_migratepages search base */
+        bool sync;                      /* Synchronous migration */
 
         /* Account for isolated anon and file pages */
         unsigned long nr_anon;
@@ -455,7 +456,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 
                 nr_migrate = cc->nr_migratepages;
                 migrate_pages(&cc->migratepages, compaction_alloc,
-                                                (unsigned long)cc, 0);
+                                (unsigned long)cc, 0,
+                                cc->sync);
                 update_nr_listpages(cc);
                 nr_remaining = cc->nr_migratepages;
 
@@ -482,7 +484,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 }
 
 unsigned long compact_zone_order(struct zone *zone,
-                                                int order, gfp_t gfp_mask)
+                                                int order, gfp_t gfp_mask,
+                                                bool sync)
 {
         struct compact_control cc = {
                 .nr_freepages = 0,
@@ -490,6 +493,7 @@ unsigned long compact_zone_order(struct zone *zone,
                 .order = order,
                 .migratetype = allocflags_to_migratetype(gfp_mask),
                 .zone = zone,
+                .sync = sync,
         };
         INIT_LIST_HEAD(&cc.freepages);
         INIT_LIST_HEAD(&cc.migratepages);
@@ -505,11 +509,13 @@ int sysctl_extfrag_threshold = 500;
  * @order: The order of the current allocation
  * @gfp_mask: The GFP mask of the current allocation
  * @nodemask: The allowed nodes to allocate from
+ * @sync: Whether migration is synchronous or not
  *
  * This is the main entry point for direct page compaction.
  */
 unsigned long try_to_compact_pages(struct zonelist *zonelist,
-                        int order, gfp_t gfp_mask, nodemask_t *nodemask)
+                        int order, gfp_t gfp_mask, nodemask_t *nodemask,
+                        bool sync)
 {
         enum zone_type high_zoneidx = gfp_zone(gfp_mask);
         int may_enter_fs = gfp_mask & __GFP_FS;
@@ -533,7 +539,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
                                                                 nodemask) {
                 int status;
 
-                status = compact_zone_order(zone, order, gfp_mask);
+                status = compact_zone_order(zone, order, gfp_mask, sync);
                 rc = max(status, rc);
 
                 /* If a normal allocation would succeed, stop compacting */