mm: compaction: fix return value of capture_free_page()

Commit ef6c5be ("fix incorrect NR_FREE_PAGES accounting (appears
like memory leak)") fixes a NR_FREE_PAGE accounting leak but missed the
return value which was also missed by this reviewer until today.

That return value is used by compaction when adding pages to a list of
isolated free pages and without this follow-up fix, there is a risk of
free list corruption.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Mel Gorman

mm/page_alloc.c

@@ -1422,7 +1422,7 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
 		}
 	}
 
-	return 1UL << order;
+	return 1UL << alloc_order;
 }
 
 /*