Commit f6ef9438 authored by Bart Samwel's avatar Bart Samwel Committed by Linus Torvalds
Browse files

[PATCH] Represent dirty_*_centisecs as jiffies internally 



Make that the internal values for:

/proc/sys/vm/dirty_writeback_centisecs
/proc/sys/vm/dirty_expire_centisecs

are stored as jiffies instead of centiseconds.  Let the sysctl interface do
the conversions with full precision using clock_t_to_jiffies, instead of
doing overflow-sensitive on-the-fly conversions every time the values are
used.

Cons: apparent precision loss if HZ is not a multiple of 100, because of
conversion back and forth.  This is a common problem for all sysctl values
that use proc_dointvec_userhz_jiffies.  (There is only one other in-tree
use, in net/core/neighbour.c.)

Signed-off-by: default avatarBart Samwel <bart@samwel.tk>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 36f57413

include/linux/writeback.h

+2 −2
Original line number Diff line number Diff line
@@ -88,8 +88,8 @@ void throttle_vm_writeout(void); 
/* These are exported to sysctl. */

extern int dirty_background_ratio;

extern int vm_dirty_ratio;

extern int dirty_writeback_centisecs;

extern int dirty_expire_centisecs;

extern int dirty_writeback_interval;

extern int dirty_expire_interval;

extern int block_dump;

extern int laptop_mode;

kernel/sysctl.c

+5 −5
Original line number Diff line number Diff line
@@ -742,18 +742,18 @@ static ctl_table vm_table[] = { 
	{

		.ctl_name	= VM_DIRTY_WB_CS,

		.procname	= "dirty_writeback_centisecs",

		.data		= &dirty_writeback_centisecs,

		.maxlen		= sizeof(dirty_writeback_centisecs),

		.data		= &dirty_writeback_interval,

		.maxlen		= sizeof(dirty_writeback_interval),

		.mode		= 0644,

		.proc_handler	= &dirty_writeback_centisecs_handler,

	},

	{

		.ctl_name	= VM_DIRTY_EXPIRE_CS,

		.procname	= "dirty_expire_centisecs",

		.data		= &dirty_expire_centisecs,

		.maxlen		= sizeof(dirty_expire_centisecs),

		.data		= &dirty_expire_interval,

		.maxlen		= sizeof(dirty_expire_interval),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

		.proc_handler	= &proc_dointvec_userhz_jiffies,

	},

	{

		.ctl_name	= VM_NR_PDFLUSH_THREADS,

mm/page-writeback.c

+12 −12
Original line number Diff line number Diff line
@@ -75,12 +75,12 @@ int vm_dirty_ratio = 40; 
 * The interval between `kupdate'-style writebacks, in centiseconds

 * (hundredths of a second)

 */

int dirty_writeback_centisecs = 5 * 100;

int dirty_writeback_interval = 5 * HZ;



/*

 * The longest number of centiseconds for which data is allowed to remain dirty

 */

int dirty_expire_centisecs = 30 * 100;

int dirty_expire_interval = 30 * HZ;



/*

 * Flag that makes the machine dump writes/reads and block dirtyings.
@@ -380,8 +380,8 @@ static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0); 
 * just walks the superblock inode list, writing back any inodes which are

 * older than a specific point in time.

 *

 * Try to run once per dirty_writeback_centisecs.  But if a writeback event

 * takes longer than a dirty_writeback_centisecs interval, then leave a

 * Try to run once per dirty_writeback_interval.  But if a writeback event

 * takes longer than a dirty_writeback_interval interval, then leave a

 * one-second gap.

 *

 * older_than_this takes precedence over nr_to_write.  So we'll only write back
@@ -406,9 +406,9 @@ static void wb_kupdate(unsigned long arg) 
	sync_supers();



	get_writeback_state(&wbs);

	oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;

	oldest_jif = jiffies - dirty_expire_interval;

	start_jif = jiffies;

	next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;

	next_jif = start_jif + dirty_writeback_interval;

	nr_to_write = wbs.nr_dirty + wbs.nr_unstable +

			(inodes_stat.nr_inodes - inodes_stat.nr_unused);

	while (nr_to_write > 0) {
@@ -425,7 +425,7 @@ static void wb_kupdate(unsigned long arg) 
	}

	if (time_before(next_jif, jiffies + HZ))

		next_jif = jiffies + HZ;

	if (dirty_writeback_centisecs)

	if (dirty_writeback_interval)

		mod_timer(&wb_timer, next_jif);

}
@@ -435,10 +435,10 @@ 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(table, write, file, buffer, length, ppos);

	if (dirty_writeback_centisecs) {

	proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);

	if (dirty_writeback_interval) {

		mod_timer(&wb_timer,

			jiffies + (dirty_writeback_centisecs * HZ) / 100);

			jiffies + dirty_writeback_interval);

		} else {

		del_timer(&wb_timer);

	}
@@ -544,7 +544,7 @@ void __init page_writeback_init(void) 
		if (vm_dirty_ratio <= 0)

			vm_dirty_ratio = 1;

	}

	mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);

	mod_timer(&wb_timer, jiffies + dirty_writeback_interval);

	set_ratelimit();

	register_cpu_notifier(&ratelimit_nb);

}

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