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: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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189d3c4a94
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6 changed files with 111 additions and 13 deletions
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@ -49,4 +49,11 @@ min_ratio (read-write)
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Minimal percentage of global dirty threshold allocated to this
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bdi. If the value written to this file would make the the sum
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of all min_ratio values exceed 100, then EINVAL is returned.
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The default is zero
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If min_ratio would become larger than the current max_ratio,
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then also EINVAL is returned. The default is zero
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max_ratio (read-write)
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Maximal percentage of global dirty threshold allocated to this
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bdi. If max_ratio would become smaller than the current
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min_ratio, then EINVAL is returned. The default is 100
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@ -52,6 +52,7 @@ struct backing_dev_info {
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int dirty_exceeded;
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unsigned int min_ratio;
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unsigned int max_ratio, max_prop_frac;
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struct device *dev;
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};
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@ -140,6 +141,7 @@ static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
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}
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int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
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int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
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/*
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* Flags in backing_dev_info::capability
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@ -77,6 +77,19 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
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local_irq_restore(flags);
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}
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/*
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* Limit the time part in order to ensure there are some bits left for the
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* cycle counter and fraction multiply.
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*/
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#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
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#define PROP_FRAC_SHIFT (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
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#define PROP_FRAC_BASE (1UL << PROP_FRAC_SHIFT)
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void __prop_inc_percpu_max(struct prop_descriptor *pd,
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struct prop_local_percpu *pl, long frac);
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/*
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* ----- SINGLE ------
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*/
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@ -73,12 +73,6 @@
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#include <linux/proportions.h>
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#include <linux/rcupdate.h>
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/*
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* Limit the time part in order to ensure there are some bits left for the
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* cycle counter.
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*/
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#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
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int prop_descriptor_init(struct prop_descriptor *pd, int shift)
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{
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int err;
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@ -267,6 +261,38 @@ void __prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
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prop_put_global(pd, pg);
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}
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/*
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* identical to __prop_inc_percpu, except that it limits this pl's fraction to
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* @frac/PROP_FRAC_BASE by ignoring events when this limit has been exceeded.
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*/
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void __prop_inc_percpu_max(struct prop_descriptor *pd,
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struct prop_local_percpu *pl, long frac)
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{
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struct prop_global *pg = prop_get_global(pd);
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prop_norm_percpu(pg, pl);
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if (unlikely(frac != PROP_FRAC_BASE)) {
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unsigned long period_2 = 1UL << (pg->shift - 1);
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unsigned long counter_mask = period_2 - 1;
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unsigned long global_count;
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long numerator, denominator;
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numerator = percpu_counter_read_positive(&pl->events);
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global_count = percpu_counter_read(&pg->events);
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denominator = period_2 + (global_count & counter_mask);
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if (numerator > ((denominator * frac) >> PROP_FRAC_SHIFT))
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goto out_put;
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}
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percpu_counter_add(&pl->events, 1);
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percpu_counter_add(&pg->events, 1);
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out_put:
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prop_put_global(pd, pg);
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}
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/*
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* Obtain a fraction of this proportion
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*
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@ -73,6 +73,24 @@ static ssize_t min_ratio_store(struct device *dev,
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}
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BDI_SHOW(min_ratio, bdi->min_ratio)
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static ssize_t max_ratio_store(struct device *dev,
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struct device_attribute *attr, const char *buf, size_t count)
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{
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struct backing_dev_info *bdi = dev_get_drvdata(dev);
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char *end;
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unsigned int ratio;
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ssize_t ret = -EINVAL;
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ratio = simple_strtoul(buf, &end, 10);
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if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
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ret = bdi_set_max_ratio(bdi, ratio);
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if (!ret)
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ret = count;
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}
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return ret;
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}
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BDI_SHOW(max_ratio, bdi->max_ratio)
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#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
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static struct device_attribute bdi_dev_attrs[] = {
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@ -82,6 +100,7 @@ static struct device_attribute bdi_dev_attrs[] = {
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__ATTR_RO(dirty_kb),
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__ATTR_RO(bdi_dirty_kb),
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__ATTR_RW(min_ratio),
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__ATTR_RW(max_ratio),
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__ATTR_NULL,
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};
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@ -147,6 +166,8 @@ int bdi_init(struct backing_dev_info *bdi)
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bdi->dev = NULL;
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bdi->min_ratio = 0;
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bdi->max_ratio = 100;
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bdi->max_prop_frac = PROP_FRAC_BASE;
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for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
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err = percpu_counter_init_irq(&bdi->bdi_stat[i], 0);
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@ -164,7 +164,8 @@ int dirty_ratio_handler(struct ctl_table *table, int write,
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*/
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static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
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{
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__prop_inc_percpu(&vm_completions, &bdi->completions);
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__prop_inc_percpu_max(&vm_completions, &bdi->completions,
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bdi->max_prop_frac);
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}
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static inline void task_dirty_inc(struct task_struct *tsk)
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@ -254,17 +255,43 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
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unsigned long flags;
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spin_lock_irqsave(&bdi_lock, flags);
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min_ratio -= bdi->min_ratio;
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if (bdi_min_ratio + min_ratio < 100) {
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bdi_min_ratio += min_ratio;
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bdi->min_ratio += min_ratio;
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} else
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if (min_ratio > bdi->max_ratio) {
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ret = -EINVAL;
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} else {
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min_ratio -= bdi->min_ratio;
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if (bdi_min_ratio + min_ratio < 100) {
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bdi_min_ratio += min_ratio;
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bdi->min_ratio += min_ratio;
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} else {
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ret = -EINVAL;
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}
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}
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spin_unlock_irqrestore(&bdi_lock, flags);
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return ret;
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}
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int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
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{
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unsigned long flags;
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int ret = 0;
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if (max_ratio > 100)
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return -EINVAL;
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spin_lock_irqsave(&bdi_lock, flags);
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if (bdi->min_ratio > max_ratio) {
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ret = -EINVAL;
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} else {
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bdi->max_ratio = max_ratio;
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bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
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}
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spin_unlock_irqrestore(&bdi_lock, flags);
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return ret;
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}
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EXPORT_SYMBOL(bdi_set_max_ratio);
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/*
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* Work out the current dirty-memory clamping and background writeout
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* thresholds.
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@ -365,6 +392,8 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
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bdi_dirty *= numerator;
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do_div(bdi_dirty, denominator);
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bdi_dirty += (dirty * bdi->min_ratio) / 100;
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if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
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bdi_dirty = dirty * bdi->max_ratio / 100;
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*pbdi_dirty = bdi_dirty;
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clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
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