mm: fix proc_dointvec_userhz_jiffies "breakage"

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=9838

On i386, HZ=1000, jiffies_to_clock_t() converts time in a somewhat strange
way from the user's point of view:

	# echo 500 >/proc/sys/vm/dirty_writeback_centisecs
	# cat /proc/sys/vm/dirty_writeback_centisecs
	499

So, we have 5000 jiffies converted to only 499 clock ticks and reported
back.

TICK_NSEC = 999848
ACTHZ = 256039

Keeping in-kernel variable in units passed from userspace will fix issue
of course, but this probably won't be right for every sysctl.

[[email protected]: coding-style fixes]
Signed-off-by: Alexey Dobriyan <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Alexey Dobriyan

include/linux/writeback.h

@@ -109,8 +109,8 @@ extern int dirty_background_ratio;
 extern unsigned long dirty_background_bytes;
 extern int vm_dirty_ratio;
 extern unsigned long vm_dirty_bytes;
-extern int dirty_writeback_interval;
-extern int dirty_expire_interval;
+extern unsigned int dirty_writeback_interval;
+extern unsigned int dirty_expire_interval;
 extern int vm_highmem_is_dirtyable;
 extern int block_dump;
 extern int laptop_mode;

kernel/sysctl.c

@@ -1010,7 +1010,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &dirty_expire_interval,
 		.maxlen		= sizeof(dirty_expire_interval),
 		.mode		= 0644,
-		.proc_handler	= &proc_dointvec_userhz_jiffies,
+		.proc_handler	= &proc_dointvec,
 	},
 	{
 		.ctl_name	= VM_NR_PDFLUSH_THREADS,

mm/page-writeback.c

@@ -92,14 +92,14 @@ int vm_dirty_ratio = 20;
 unsigned long vm_dirty_bytes;
 
 /*
- * The interval between `kupdate'-style writebacks, in jiffies
+ * The interval between `kupdate'-style writebacks
  */
-int dirty_writeback_interval = 5 * HZ;
+unsigned int dirty_writeback_interval = 5 * 100; /* sentiseconds */
 
 /*
- * The longest number of jiffies for which data is allowed to remain dirty
+ * The longest time for which data is allowed to remain dirty
  */
-int dirty_expire_interval = 30 * HZ;
+unsigned int dirty_expire_interval = 30 * 100; /* sentiseconds */
 
 /*
  * Flag that makes the machine dump writes/reads and block dirtyings.
@@ -770,9 +770,9 @@ static void wb_kupdate(unsigned long arg)
 
 	sync_supers();
 
-	oldest_jif = jiffies - dirty_expire_interval;
+	oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval);
 	start_jif = jiffies;
-	next_jif = start_jif + dirty_writeback_interval;
+	next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10);
 	nr_to_write = global_page_state(NR_FILE_DIRTY) +
 			global_page_state(NR_UNSTABLE_NFS) +
 			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
@@ -801,9 +801,10 @@ static void wb_kupdate(unsigned long arg)
 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 	struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 {
-	proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
+	proc_dointvec(table, write, file, buffer, length, ppos);
 	if (dirty_writeback_interval)
-		mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
+		mod_timer(&wb_timer, jiffies +
+			msecs_to_jiffies(dirty_writeback_interval * 10));
 	else
 		del_timer(&wb_timer);
 	return 0;
@@ -905,7 +906,8 @@ void __init page_writeback_init(void)
 {
 	int shift;
 
-	mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
+	mod_timer(&wb_timer,
+		  jiffies + msecs_to_jiffies(dirty_writeback_interval * 10));
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);