[PATCH 2/4] Make page-writeback timers 1 sec jiffy aligned

[PATCH 2/4] Make page-writeback timers 1 sec jiffy aligned

[Venki Pallipadi]

timer round_jiffies in page-writeback.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

Index: linux-2.6.22-rc-mm/mm/page-writeback.c
===================================================================
--- linux-2.6.22-rc-mm.orig/mm/page-writeback.c	2007-05-25 10:49:11.000000000 -0700
+++ linux-2.6.22-rc-mm/mm/page-writeback.c	2007-05-25 10:49:29.000000000 -0700
@@ -469,7 +469,7 @@
 	if (time_before(next_jif, jiffies + HZ))
 		next_jif = jiffies + HZ;
 	if (dirty_writeback_interval)
-		mod_timer(&wb_timer, next_jif);
+		mod_timer(&wb_timer, round_jiffies(next_jif));
 }
 
 /*
@@ -481,7 +481,7 @@
 	proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
 	if (dirty_writeback_interval) {
 		mod_timer(&wb_timer,
-			jiffies + dirty_writeback_interval);
+			round_jiffies(jiffies + dirty_writeback_interval));
 		} else {
 		del_timer(&wb_timer);
 	}
@@ -491,7 +491,8 @@
 static void wb_timer_fn(unsigned long unused)
 {
 	if (pdflush_operation(wb_kupdate, 0) < 0)
-		mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
+		mod_timer(&wb_timer, round_jiffies(jiffies + HZ));
+		/* delay 1 second */
 }
 
 static void laptop_flush(unsigned long unused)
@@ -511,7 +512,7 @@
  */
 void laptop_io_completion(void)
 {
-	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
+	mod_timer(&laptop_mode_wb_timer, round_jiffies(jiffies + laptop_mode));
 }
 
 /*
@@ -582,7 +583,7 @@
  */
 void __init page_writeback_init(void)
 {
-	mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
+	mod_timer(&wb_timer, round_jiffies(jiffies + dirty_writeback_interval));
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);
 }

Re: [PATCH 2/4] Make page-writeback timers 1 sec jiffy aligned

[Andrew Morton]

On Tue, 29 May 2007 10:59:51 -0700
Venki Pallipadi <venkatesh.pallipadi@intel.com> wrote:

> 
> 
> timer round_jiffies in page-writeback.
> 
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
> 
> Index: linux-2.6.22-rc-mm/mm/page-writeback.c
> ===================================================================
> --- linux-2.6.22-rc-mm.orig/mm/page-writeback.c	2007-05-25 10:49:11.000000000 -0700
> +++ linux-2.6.22-rc-mm/mm/page-writeback.c	2007-05-25 10:49:29.000000000 -0700
> @@ -469,7 +469,7 @@
>  	if (time_before(next_jif, jiffies + HZ))
>  		next_jif = jiffies + HZ;
>  	if (dirty_writeback_interval)
> -		mod_timer(&wb_timer, next_jif);
> +		mod_timer(&wb_timer, round_jiffies(next_jif));
>  }
>  
>  /*
> @@ -481,7 +481,7 @@
>  	proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
>  	if (dirty_writeback_interval) {
>  		mod_timer(&wb_timer,
> -			jiffies + dirty_writeback_interval);
> +			round_jiffies(jiffies + dirty_writeback_interval));
>  		} else {
>  		del_timer(&wb_timer);
>  	}

mutter.

These tunables are in units of centiseconds, so the user can indeed set the
writeback interval to, say, 0.2 seconds.  People have played with that sort
of thing.

I doubt if this patch will hurt anyone much, but it is an incompatible
user-visible change.

Probably a suitable heuristic for fixing this would be to only do the
rounding if dirty_writeback_interval is a multiple of HZ.  In the vast
majority of cases, that will be true.