oom: prevent including sched.h in header file

It's not necessary to include all of linux/sched.h in linux/oom.h.  Instead,
simply include prototypes for the relevant structs and include linux/types.h
for gfp_t.

Cc: Andrea Arcangeli <[email protected]>
Cc: Christoph Lameter <[email protected]>
Acked-by: Alexey Dobriyan <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/oom.h

@@ -1,8 +1,6 @@
 #ifndef __INCLUDE_LINUX_OOM_H
 #define __INCLUDE_LINUX_OOM_H
 
-#include <linux/sched.h>
-
 /* /proc/<pid>/oom_adj set to -17 protects from the oom-killer */
 #define OOM_DISABLE (-17)
 /* inclusive */
@@ -11,6 +9,11 @@
 
 #ifdef __KERNEL__
 
+#include <linux/types.h>
+
+struct zonelist;
+struct notifier_block;
+
 /*
  * Types of limitations to the nodes from which allocations may occur
  */