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block: Convert BDI proportion calculations to flexible proportions
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Convert calculations of proportion of writeback each bdi does to new flexible
proportion code. That allows us to use aging period of fixed wallclock time
which gives better proportion estimates given the hugely varying throughput of
different devices.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
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@jankara
jankara authored and Fengguang Wu committed Jun 8, 2012
1 parent e78d483 commit eb608e3
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Showing 3 changed files with 69 additions and 44 deletions.
4 changes: 2 additions & 2 deletions include/linux/backing-dev.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@

#include <linux/percpu_counter.h>
#include <linux/log2.h>
#include <linux/proportions.h>
#include <linux/flex_proportions.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/sched.h>
Expand Down Expand Up @@ -89,7 +89,7 @@ struct backing_dev_info {
unsigned long dirty_ratelimit;
unsigned long balanced_dirty_ratelimit;

struct prop_local_percpu completions;
struct fprop_local_percpu completions;
int dirty_exceeded;

unsigned int min_ratio;
Expand Down
6 changes: 3 additions & 3 deletions mm/backing-dev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -677,7 +677,7 @@ int bdi_init(struct backing_dev_info *bdi)

bdi->min_ratio = 0;
bdi->max_ratio = 100;
bdi->max_prop_frac = PROP_FRAC_BASE;
bdi->max_prop_frac = FPROP_FRAC_BASE;
spin_lock_init(&bdi->wb_lock);
INIT_LIST_HEAD(&bdi->bdi_list);
INIT_LIST_HEAD(&bdi->work_list);
Expand All @@ -700,7 +700,7 @@ int bdi_init(struct backing_dev_info *bdi)
bdi->write_bandwidth = INIT_BW;
bdi->avg_write_bandwidth = INIT_BW;

err = prop_local_init_percpu(&bdi->completions);
err = fprop_local_init_percpu(&bdi->completions);

if (err) {
err:
Expand Down Expand Up @@ -744,7 +744,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
percpu_counter_destroy(&bdi->bdi_stat[i]);

prop_local_destroy_percpu(&bdi->completions);
fprop_local_destroy_percpu(&bdi->completions);
}
EXPORT_SYMBOL(bdi_destroy);

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103 changes: 64 additions & 39 deletions mm/page-writeback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@
#include <linux/syscalls.h>
#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
#include <linux/pagevec.h>
#include <linux/timer.h>
#include <trace/events/writeback.h>

/*
Expand Down Expand Up @@ -135,7 +136,20 @@ unsigned long global_dirty_limit;
* measured in page writeback completions.
*
*/
static struct prop_descriptor vm_completions;
static struct fprop_global writeout_completions;

static void writeout_period(unsigned long t);
/* Timer for aging of writeout_completions */
static struct timer_list writeout_period_timer =
TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
static unsigned long writeout_period_time = 0;

/*
* Length of period for aging writeout fractions of bdis. This is an
* arbitrarily chosen number. The longer the period, the slower fractions will
* reflect changes in current writeout rate.
*/
#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)

/*
* Work out the current dirty-memory clamping and background writeout
Expand Down Expand Up @@ -322,34 +336,6 @@ bool zone_dirty_ok(struct zone *zone)
zone_page_state(zone, NR_WRITEBACK) <= limit;
}

/*
* couple the period to the dirty_ratio:
*
* period/2 ~ roundup_pow_of_two(dirty limit)
*/
static int calc_period_shift(void)
{
unsigned long dirty_total;

if (vm_dirty_bytes)
dirty_total = vm_dirty_bytes / PAGE_SIZE;
else
dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
100;
return 2 + ilog2(dirty_total - 1);
}

/*
* update the period when the dirty threshold changes.
*/
static void update_completion_period(void)
{
int shift = calc_period_shift();
prop_change_shift(&vm_completions, shift);

writeback_set_ratelimit();
}

int dirty_background_ratio_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
Expand Down Expand Up @@ -383,7 +369,7 @@ int dirty_ratio_handler(struct ctl_table *table, int write,

ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
update_completion_period();
writeback_set_ratelimit();
vm_dirty_bytes = 0;
}
return ret;
Expand All @@ -398,21 +384,41 @@ int dirty_bytes_handler(struct ctl_table *table, int write,

ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
update_completion_period();
writeback_set_ratelimit();
vm_dirty_ratio = 0;
}
return ret;
}

static unsigned long wp_next_time(unsigned long cur_time)
{
cur_time += VM_COMPLETIONS_PERIOD_LEN;
/* 0 has a special meaning... */
if (!cur_time)
return 1;
return cur_time;
}

/*
* Increment the BDI's writeout completion count and the global writeout
* completion count. Called from test_clear_page_writeback().
*/
static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
{
__inc_bdi_stat(bdi, BDI_WRITTEN);
__prop_inc_percpu_max(&vm_completions, &bdi->completions,
bdi->max_prop_frac);
__fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
bdi->max_prop_frac);
/* First event after period switching was turned off? */
if (!unlikely(writeout_period_time)) {
/*
* We can race with other __bdi_writeout_inc calls here but
* it does not cause any harm since the resulting time when
* timer will fire and what is in writeout_period_time will be
* roughly the same.
*/
writeout_period_time = wp_next_time(jiffies);
mod_timer(&writeout_period_timer, writeout_period_time);
}
}

void bdi_writeout_inc(struct backing_dev_info *bdi)
Expand All @@ -431,10 +437,32 @@ EXPORT_SYMBOL_GPL(bdi_writeout_inc);
static void bdi_writeout_fraction(struct backing_dev_info *bdi,
long *numerator, long *denominator)
{
prop_fraction_percpu(&vm_completions, &bdi->completions,
fprop_fraction_percpu(&writeout_completions, &bdi->completions,
numerator, denominator);
}

/*
* On idle system, we can be called long after we scheduled because we use
* deferred timers so count with missed periods.
*/
static void writeout_period(unsigned long t)
{
int miss_periods = (jiffies - writeout_period_time) /
VM_COMPLETIONS_PERIOD_LEN;

if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
writeout_period_time = wp_next_time(writeout_period_time +
miss_periods * VM_COMPLETIONS_PERIOD_LEN);
mod_timer(&writeout_period_timer, writeout_period_time);
} else {
/*
* Aging has zeroed all fractions. Stop wasting CPU on period
* updates.
*/
writeout_period_time = 0;
}
}

/*
* bdi_min_ratio keeps the sum of the minimum dirty shares of all
* registered backing devices, which, for obvious reasons, can not
Expand Down Expand Up @@ -475,7 +503,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
ret = -EINVAL;
} else {
bdi->max_ratio = max_ratio;
bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
}
spin_unlock_bh(&bdi_lock);

Expand Down Expand Up @@ -1606,13 +1634,10 @@ static struct notifier_block __cpuinitdata ratelimit_nb = {
*/
void __init page_writeback_init(void)
{
int shift;

writeback_set_ratelimit();
register_cpu_notifier(&ratelimit_nb);

shift = calc_period_shift();
prop_descriptor_init(&vm_completions, shift);
fprop_global_init(&writeout_completions);
}

/**
Expand Down

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