mm: compaction: introduce map_pages()

This commit creates a map_pages() function which map pages freed
using split_free_pages().  This merely moves some code from
isolate_freepages() so that it can be reused in other places.
Signed-off-by: NMichal Nazarewicz <mina86@mina86.com>
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: NRobert Nelson <robertcnelson@gmail.com>
Tested-by: NBarry Song <Baohua.Song@csr.com>

mm/compaction.c

@@ -127,6 +127,16 @@ static bool suitable_migration_target(struct page *page)
 	return false;
 }
 
+static void map_pages(struct list_head *list)
+{
+	struct page *page;
+
+	list_for_each_entry(page, list, lru) {
+		arch_alloc_page(page, 0);
+		kernel_map_pages(page, 1, 1);
+	}
+}
+
 /*
  * Based on information in the current compact_control, find blocks
  * suitable for isolating free pages from and then isolate them.
@@ -206,10 +216,7 @@ static void isolate_freepages(struct zone *zone,
 	}
 
 	/* split_free_page does not map the pages */
-	list_for_each_entry(page, freelist, lru) {
-		arch_alloc_page(page, 0);
-		kernel_map_pages(page, 1, 1);
-	}
+	map_pages(freelist);
 
 	cc->free_pfn = high_pfn;
 	cc->nr_freepages = nr_freepages;