thp: transhuge isolate_migratepages()

It's not worth migrating transparent hugepages during compaction.  Those
hugepages don't create fragmentation.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index b0fbfdfad298..da25b5a2e476 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -295,10 +295,25 @@ static unsigned long isolate_migratepages(struct zone *zone,
                         continue;
                 }
 
+                if (!PageLRU(page))
+                        continue;
+
+                /*
+                 * PageLRU is set, and lru_lock excludes isolation,
+                 * splitting and collapsing (collapsing has already
+                 * happened if PageLRU is set).
+                 */
+                if (PageTransHuge(page)) {
+                        low_pfn += (1 << compound_order(page)) - 1;
+                        continue;
+                }
+
                 /* Try isolate the page */
                 if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
                         continue;
 
+                VM_BUG_ON(PageTransCompound(page));
+
                 /* Successfully isolated */
                 del_page_from_lru_list(zone, page, page_lru(page));
                 list_add(&page->lru, migratelist);