Fix compile error
 fs/fs-writeback.c:515:33: error: ‘PAGE_CACHE_SHIFT’ undeclared (first use in this function)
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
 #include <linux/sched.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/pagemap.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/writeback.h>
 #include <linux/tracepoint.h>
 #include "internal.h"
 
+/*
+ * 4MB minimal write chunk size
+ */
+#define MIN_WRITEBACK_PAGES    (4096UL >> (PAGE_CACHE_SHIFT - 10))
+
 /*
  * Passed into wb_writeback(), essentially a subset of writeback_control
  */
 
 #define DIRTY_SCOPE            8
 #define DIRTY_FULL_SCOPE       (DIRTY_SCOPE / 2)
 
-/*
- * 4MB minimal write chunk size
- */
-#define MIN_WRITEBACK_PAGES    (4096UL >> (PAGE_CACHE_SHIFT - 10))
-
 struct backing_dev_info;
 
 /*