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.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 9 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6aa92b03c747..30351f0063ac 100644
--- a/mm/page-writeback.c
+++ b/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);