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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>
This commit is contained in:
Alexey Dobriyan 2009-03-31 15:23:18 -07:00 committed by Linus Torvalds
parent 6a11f75b6a
commit 704503d836
3 changed files with 14 additions and 12 deletions
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4
include/linux/writeback.h
View File

@ -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;

2
kernel/sysctl.c
View File

@ -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,

20
mm/page-writeback.c
View File

@ -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);