writeback: move MIN_WRITEBACK_PAGES to fs-writeback.c

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>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 92d353e069dc..22e2d42742a9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -20,6 +20,7 @@
 #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>
@@ -30,6 +31,11 @@
 #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
  */
 struct wb_writeback_work {