From bc835011afbea3957217ee716093d791fb2fe44f Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Thu, 13 Jan 2011 15:47:08 -0800
Subject: [PATCH] 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>
---
 mm/compaction.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

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);