mm: fix warnings regarding enum migrate_mode

sparc64 allmodconfig:

In file included from include/linux/compat.h:15,
                 from /usr/src/25/arch/sparc/include/asm/siginfo.h:19,
                 from include/linux/signal.h:5,
                 from include/linux/sched.h:73,
                 from arch/sparc/kernel/asm-offsets.c:13:
include/linux/fs.h:618: warning: parameter has incomplete type

It seems that my sparc64 compiler (gcc-3.4.5) doesn't like the forward
declaration of enums.

Fix this by moving the "enum migrate_mode" definition into its own header
file.
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andy Isaacson <adi@hexapodia.org>
Cc: Nai Xia <nai.xia@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fs.h

@@ -10,6 +10,7 @@
 #include <linux/ioctl.h>
 #include <linux/blk_types.h>
 #include <linux/types.h>
+#include <linux/migrate_mode.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -526,7 +527,6 @@ enum positive_aop_returns {
 struct page;
 struct address_space;
 struct writeback_control;
-enum migrate_mode;
 
 struct iov_iter {
 	const struct iovec *iov;

include/linux/migrate.h

@@ -3,22 +3,10 @@
 
 #include <linux/mm.h>
 #include <linux/mempolicy.h>
+#include <linux/migrate_mode.h>
 
 typedef struct page *new_page_t(struct page *, unsigned long private, int **);
 
-/*
- * MIGRATE_ASYNC means never block
- * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
- *	on most operations but not ->writepage as the potential stall time
- *	is too significant
- * MIGRATE_SYNC will block when migrating pages
- */
-enum migrate_mode {
-	MIGRATE_ASYNC,
-	MIGRATE_SYNC_LIGHT,
-	MIGRATE_SYNC,
-};
-
 #ifdef CONFIG_MIGRATION
 #define PAGE_MIGRATION 1
 

include/linux/migrate_mode.h

+#ifndef MIGRATE_MODE_H_INCLUDED
+#define MIGRATE_MODE_H_INCLUDED
+/*
+ * MIGRATE_ASYNC means never block
+ * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
+ *	on most operations but not ->writepage as the potential stall time
+ *	is too significant
+ * MIGRATE_SYNC will block when migrating pages
+ */
+enum migrate_mode {
+	MIGRATE_ASYNC,
+	MIGRATE_SYNC_LIGHT,
+	MIGRATE_SYNC,
+};
+
+#endif		/* MIGRATE_MODE_H_INCLUDED */