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>

diff --git a/mm/compaction.c b/mm/compaction.c
index b0fbfdf..da25b5a 100644 (file)
--- 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);