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Commit 189d3c4a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
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mm: bdi: allow setting a minimum for the bdi dirty limit 



Under normal circumstances each device is given a part of the total write-back
cache that relates to its current avg writeout speed in relation to the other
devices.

min_ratio - allows one to assign a minimum portion of the write-back cache to
a particular device.  This is useful in situations where you might want to
provide a minimum QoS.  (One request for this feature came from flash based
storage people who wanted to avoid writing out at all costs - they of course
needed some pdflush hacks as well)

max_ratio - allows one to assign a maximum portion of the dirty limit to a
particular device.  This is useful in situations where you want to avoid one
device taking all or most of the write-back cache.  Eg.  an NFS mount that is
prone to get stuck, or a FUSE mount which you don't trust to play fair.

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

[mszeredi@suse.cz]

 - fix parsing in min_ratio_store()
 - 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 b6f2fcbc

Documentation/ABI/testing/sysfs-class-bdi

+6 −0
Original line number Diff line number Diff line
@@ -44,3 +44,9 @@ bdi_dirty_kb (read-only) 
	Current threshold on this BDI for reclaimable + writeback

	memory



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

include/linux/backing-dev.h

+4 −0
Original line number Diff line number Diff line
@@ -51,6 +51,8 @@ struct backing_dev_info { 
	struct prop_local_percpu completions;

	int dirty_exceeded;



	unsigned int min_ratio;



	struct device *dev;

};
@@ -137,6 +139,8 @@ static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi) 
#endif

}



int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);



/*

 * Flags in backing_dev_info::capability

 * - The first two flags control whether dirty pages will contribute to the

mm/backing-dev.c

+21 −0
Original line number Diff line number Diff line
@@ -55,6 +55,24 @@ static inline unsigned long get_dirty(struct backing_dev_info *bdi, int i) 
BDI_SHOW(dirty_kb, K(get_dirty(bdi, 1)))

BDI_SHOW(bdi_dirty_kb, K(get_dirty(bdi, 2)))



static ssize_t min_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_min_ratio(bdi, ratio);

		if (!ret)

			ret = count;

	}

	return ret;

}

BDI_SHOW(min_ratio, bdi->min_ratio)



#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)



static struct device_attribute bdi_dev_attrs[] = {
@@ -63,6 +81,7 @@ static struct device_attribute bdi_dev_attrs[] = { 
	__ATTR_RO(writeback_kb),

	__ATTR_RO(dirty_kb),

	__ATTR_RO(bdi_dirty_kb),

	__ATTR_RW(min_ratio),

	__ATTR_NULL,

};
@@ -127,6 +146,8 @@ int bdi_init(struct backing_dev_info *bdi) 


	bdi->dev = NULL;



	bdi->min_ratio = 0;



	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {

		err = percpu_counter_init_irq(&bdi->bdi_stat[i], 0);

		if (err)

mm/page-writeback.c

+26 −1
Original line number Diff line number Diff line
@@ -242,6 +242,29 @@ static void task_dirty_limit(struct task_struct *tsk, long *pdirty) 
	*pdirty = dirty;

}



/*

 *

 */

static DEFINE_SPINLOCK(bdi_lock);

static unsigned int bdi_min_ratio;



int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)

{

	int ret = 0;

	unsigned long flags;



	spin_lock_irqsave(&bdi_lock, flags);

	min_ratio -= bdi->min_ratio;

	if (bdi_min_ratio + min_ratio < 100) {

		bdi_min_ratio += min_ratio;

		bdi->min_ratio += min_ratio;

	} else

		ret = -EINVAL;

	spin_unlock_irqrestore(&bdi_lock, flags);



	return ret;

}



/*

 * Work out the current dirty-memory clamping and background writeout

 * thresholds.
@@ -330,7 +353,7 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty, 
	*pdirty = dirty;



	if (bdi) {

		u64 bdi_dirty = dirty;

		u64 bdi_dirty;

		long numerator, denominator;



		/*
@@ -338,8 +361,10 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty, 
		 */

		bdi_writeout_fraction(bdi, &numerator, &denominator);



		bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;

		bdi_dirty *= numerator;

		do_div(bdi_dirty, denominator);

		bdi_dirty += (dirty * bdi->min_ratio) / 100;



		*pbdi_dirty = bdi_dirty;

		clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);