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, 15 insertions, 6 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 03a66a31bfcd..0fd486467b4b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1812,7 +1812,8 @@ static struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
         struct zonelist *zonelist, enum zone_type high_zoneidx,
         nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
-        int migratetype, unsigned long *did_some_progress)
+        int migratetype, unsigned long *did_some_progress,
+        bool sync_migration)
 {
         struct page *page;
         struct task_struct *tsk = current;
@@ -1822,7 +1823,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 
         tsk->flags |= PF_MEMALLOC;
         *did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
-                                                                nodemask);
+                                                nodemask, sync_migration);
         tsk->flags &= ~PF_MEMALLOC;
         if (*did_some_progress != COMPACT_SKIPPED) {
 
@@ -1859,7 +1860,8 @@ static inline struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
         struct zonelist *zonelist, enum zone_type high_zoneidx,
         nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
-        int migratetype, unsigned long *did_some_progress)
+        int migratetype, unsigned long *did_some_progress,
+        bool sync_migration)
 {
         return NULL;
 }
@@ -2001,6 +2003,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
         unsigned long pages_reclaimed = 0;
         unsigned long did_some_progress;
         struct task_struct *p = current;
+        bool sync_migration = false;
 
         /*
          * In the slowpath, we sanity check order to avoid ever trying to
@@ -2063,14 +2066,19 @@ rebalance:
         if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
                 goto nopage;
 
-        /* Try direct compaction */
+        /*
+         * Try direct compaction. The first pass is asynchronous. Subsequent
+         * attempts after direct reclaim are synchronous
+         */
         page = __alloc_pages_direct_compact(gfp_mask, order,
                                         zonelist, high_zoneidx,
                                         nodemask,
                                         alloc_flags, preferred_zone,
-                                        migratetype, &did_some_progress);
+                                        migratetype, &did_some_progress,
+                                        sync_migration);
         if (page)
                 goto got_pg;
+        sync_migration = true;
 
         /* Try direct reclaim and then allocating */
         page = __alloc_pages_direct_reclaim(gfp_mask, order,
@@ -2134,7 +2142,8 @@ rebalance:
                                         zonelist, high_zoneidx,
                                         nodemask,
                                         alloc_flags, preferred_zone,
-                                        migratetype, &did_some_progress);
+                                        migratetype, &did_some_progress,
+                                        sync_migration);
                 if (page)
                         goto got_pg;
         }