[PATCH] Represent laptop_mode as jiffies internally

Make that the internal value for /proc/sys/vm/laptop_mode is stored as
jiffies instead of seconds.  Let the sysctl interface do the conversions,
instead of doing on-the-fly conversions every time the value is used.

Add a description of the fact that laptop_mode doubles as a flag and a
timeout to the comment above the laptop_mode variable.

Signed-off-by: Bart Samwel <bart@samwel.tk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sysctl.c

@@ -848,9 +848,8 @@ static ctl_table vm_table[] = {
 		.data		= &laptop_mode,
 		.maxlen		= sizeof(laptop_mode),
 		.mode		= 0644,
-		.proc_handler	= &proc_dointvec,
-		.strategy	= &sysctl_intvec,
-		.extra1		= &zero,
+		.proc_handler	= &proc_dointvec_jiffies,
+		.strategy	= &sysctl_jiffies,
 	},
 	{
 		.ctl_name	= VM_BLOCK_DUMP,

mm/page-writeback.c

@@ -88,7 +88,8 @@ int dirty_expire_interval = 30 * HZ;
 int block_dump;
 
 /*
- * Flag that puts the machine in "laptop mode".
+ * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
+ * a full sync is triggered after this time elapses without any disk activity.
  */
 int laptop_mode;
 
@@ -468,7 +469,7 @@ static void laptop_timer_fn(unsigned long unused)
  */
 void laptop_io_completion(void)
 {
-	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
+	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
 }
 
 /*