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>

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 7300ecdc480c93b3e2010fecb41b9ceefb680799..93445477f86a7cdfe8352e15e21fbad77d9f7f0a 100644 (file)
--- a/include/linux/writeback.h
+++ b/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;

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c5ef44ff850f5af111943d76a5484318d6a5bc35..2e490a389dd2313c4c0a5f17dbc38c2f933e97eb 100644 (file)
--- a/kernel/sysctl.c
+++ b/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,

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6aa92b03c74704f328d157d8e6e84c340e42d6c5..30351f0063acb125f4581f0a1c6197662254d8ab 100644 (file)
--- 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);