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, 2 insertions, 2 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 11ff260fb282..9db274593086 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -935,7 +935,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
                 return PTR_ERR(vma);
 
         if (!list_empty(&pagelist)) {
-                err = migrate_pages(&pagelist, new_node_page, dest, 0);
+                err = migrate_pages(&pagelist, new_node_page, dest, 0, true);
                 if (err)
                         putback_lru_pages(&pagelist);
         }
@@ -1155,7 +1155,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 
                 if (!list_empty(&pagelist)) {
                         nr_failed = migrate_pages(&pagelist, new_vma_page,
-                                                (unsigned long)vma, 0);
+                                                (unsigned long)vma, 0, true);
                         if (nr_failed)
                                 putback_lru_pages(&pagelist);
                 }