Commit a42dde04 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds

mm: bdi: allow setting a maximum for the bdi dirty limit

Add "max_ratio" to /sys/class/bdi.  This indicates the maximum percentage of
the global dirty threshold allocated to this bdi.

[mszeredi@suse.cz]

 - fix parsing in max_ratio_store().
 - export bdi_set_max_ratio() to modules
 - limit bdi_dirty with bdi->max_ratio
 - document new sysfs attribute
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 189d3c4a
......@@ -49,4 +49,11 @@ min_ratio (read-write)
Minimal percentage of global dirty threshold allocated to this
bdi. If the value written to this file would make the the sum
of all min_ratio values exceed 100, then EINVAL is returned.
The default is zero
If min_ratio would become larger than the current max_ratio,
then also EINVAL is returned. The default is zero
max_ratio (read-write)
Maximal percentage of global dirty threshold allocated to this
bdi. If max_ratio would become smaller than the current
min_ratio, then EINVAL is returned. The default is 100
......@@ -52,6 +52,7 @@ struct backing_dev_info {
int dirty_exceeded;
unsigned int min_ratio;
unsigned int max_ratio, max_prop_frac;
struct device *dev;
};
......@@ -140,6 +141,7 @@ static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
}
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
/*
* Flags in backing_dev_info::capability
......
......@@ -77,6 +77,19 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
local_irq_restore(flags);
}
/*
* Limit the time part in order to ensure there are some bits left for the
* cycle counter and fraction multiply.
*/
#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
#define PROP_FRAC_SHIFT (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
#define PROP_FRAC_BASE (1UL << PROP_FRAC_SHIFT)
void __prop_inc_percpu_max(struct prop_descriptor *pd,
struct prop_local_percpu *pl, long frac);
/*
* ----- SINGLE ------
*/
......
......@@ -73,12 +73,6 @@
#include <linux/proportions.h>
#include <linux/rcupdate.h>
/*
* Limit the time part in order to ensure there are some bits left for the
* cycle counter.
*/
#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
int prop_descriptor_init(struct prop_descriptor *pd, int shift)
{
int err;
......@@ -267,6 +261,38 @@ void __prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
prop_put_global(pd, pg);
}
/*
* identical to __prop_inc_percpu, except that it limits this pl's fraction to
* @frac/PROP_FRAC_BASE by ignoring events when this limit has been exceeded.
*/
void __prop_inc_percpu_max(struct prop_descriptor *pd,
struct prop_local_percpu *pl, long frac)
{
struct prop_global *pg = prop_get_global(pd);
prop_norm_percpu(pg, pl);
if (unlikely(frac != PROP_FRAC_BASE)) {
unsigned long period_2 = 1UL << (pg->shift - 1);
unsigned long counter_mask = period_2 - 1;
unsigned long global_count;
long numerator, denominator;
numerator = percpu_counter_read_positive(&pl->events);
global_count = percpu_counter_read(&pg->events);
denominator = period_2 + (global_count & counter_mask);
if (numerator > ((denominator * frac) >> PROP_FRAC_SHIFT))
goto out_put;
}
percpu_counter_add(&pl->events, 1);
percpu_counter_add(&pg->events, 1);
out_put:
prop_put_global(pd, pg);
}
/*
* Obtain a fraction of this proportion
*
......
......@@ -73,6 +73,24 @@ static ssize_t min_ratio_store(struct device *dev,
}
BDI_SHOW(min_ratio, bdi->min_ratio)
static ssize_t max_ratio_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
struct backing_dev_info *bdi = dev_get_drvdata(dev);
char *end;
unsigned int ratio;
ssize_t ret = -EINVAL;
ratio = simple_strtoul(buf, &end, 10);
if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
ret = bdi_set_max_ratio(bdi, ratio);
if (!ret)
ret = count;
}
return ret;
}
BDI_SHOW(max_ratio, bdi->max_ratio)
#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
static struct device_attribute bdi_dev_attrs[] = {
......@@ -82,6 +100,7 @@ static struct device_attribute bdi_dev_attrs[] = {
__ATTR_RO(dirty_kb),
__ATTR_RO(bdi_dirty_kb),
__ATTR_RW(min_ratio),
__ATTR_RW(max_ratio),
__ATTR_NULL,
};
......@@ -147,6 +166,8 @@ int bdi_init(struct backing_dev_info *bdi)
bdi->dev = NULL;
bdi->min_ratio = 0;
bdi->max_ratio = 100;
bdi->max_prop_frac = PROP_FRAC_BASE;
for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
err = percpu_counter_init_irq(&bdi->bdi_stat[i], 0);
......
......@@ -164,7 +164,8 @@ int dirty_ratio_handler(struct ctl_table *table, int write,
*/
static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
{
__prop_inc_percpu(&vm_completions, &bdi->completions);
__prop_inc_percpu_max(&vm_completions, &bdi->completions,
bdi->max_prop_frac);
}
static inline void task_dirty_inc(struct task_struct *tsk)
......@@ -254,16 +255,42 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
unsigned long flags;
spin_lock_irqsave(&bdi_lock, flags);
if (min_ratio > bdi->max_ratio) {
ret = -EINVAL;
} else {
min_ratio -= bdi->min_ratio;
if (bdi_min_ratio + min_ratio < 100) {
bdi_min_ratio += min_ratio;
bdi->min_ratio += min_ratio;
} else
} else {
ret = -EINVAL;
}
}
spin_unlock_irqrestore(&bdi_lock, flags);
return ret;
}
int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
{
unsigned long flags;
int ret = 0;
if (max_ratio > 100)
return -EINVAL;
spin_lock_irqsave(&bdi_lock, flags);
if (bdi->min_ratio > max_ratio) {
ret = -EINVAL;
} else {
bdi->max_ratio = max_ratio;
bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
}
spin_unlock_irqrestore(&bdi_lock, flags);
return ret;
}
EXPORT_SYMBOL(bdi_set_max_ratio);
/*
* Work out the current dirty-memory clamping and background writeout
......@@ -365,6 +392,8 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
bdi_dirty *= numerator;
do_div(bdi_dirty, denominator);
bdi_dirty += (dirty * bdi->min_ratio) / 100;
if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
bdi_dirty = dirty * bdi->max_ratio / 100;
*pbdi_dirty = bdi_dirty;
clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
......
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