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

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

Documentation/ABI/testing/sysfs-class-bdi

+8 −1
Original line number Diff line number Diff line
@@ -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

include/linux/backing-dev.h

+2 −0
Original line number Diff line number Diff line
@@ -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

include/linux/proportions.h

+13 −0
Original line number Diff line number Diff line
@@ -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 ------

 */

lib/proportions.c

+32 −6
Original line number Diff line number Diff line
@@ -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

 *

mm/backing-dev.c

+21 −0
Original line number Diff line number Diff line
@@ -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);