mm: add comments to explain mm_struct fields

Add comments to explain the page statistics field in the mm_struct.

[akpm@linux-foundation.org: add missing ;]
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm_types.h

@@ -304,8 +304,15 @@ struct mm_struct {
 	unsigned long hiwater_rss;	/* High-watermark of RSS usage */
 	unsigned long hiwater_vm;	/* High-water virtual memory usage */
 
-	unsigned long total_vm, locked_vm, pinned_vm, shared_vm, exec_vm;
-	unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;
+	unsigned long total_vm;		/* Total pages mapped */
+	unsigned long locked_vm;	/* Pages that have PG_mlocked set */
+	unsigned long pinned_vm;	/* Refcount permanently increased */
+	unsigned long shared_vm;	/* Shared pages (files) */
+	unsigned long exec_vm;		/* VM_EXEC & ~VM_WRITE */
+	unsigned long stack_vm;		/* VM_GROWSUP/DOWN */
+	unsigned long reserved_vm;	/* VM_RESERVED|VM_IO pages */
+	unsigned long def_flags;
+	unsigned long nr_ptes;		/* Page table pages */
 	unsigned long start_code, end_code, start_data, end_data;
 	unsigned long start_brk, brk, start_stack;
 	unsigned long arg_start, arg_end, env_start, env_end;