Commit 704503d8 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds
Browse files

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: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6a11f75b

include/linux/writeback.h

+2 −2
Original line number Diff line number Diff line
@@ -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

+1 −1
Original line number Diff line number Diff line
@@ -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

+11 −9
Original line number Diff line number Diff line
@@ -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);

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