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Subject[patch 5/6] mm: bdi: allow setting a minimum for the bdi dirty limit
From: Peter Zijlstra <a.p.zijlstra@chello.nl>

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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/include/linux/backing-dev.h
===================================================================
--- linux.orig/include/linux/backing-dev.h 2008-01-29 14:40:35.000000000 +0100
+++ linux/include/linux/backing-dev.h 2008-01-29 15:35:34.000000000 +0100
@@ -51,6 +51,8 @@ struct backing_dev_info {
struct prop_local_percpu completions;
int dirty_exceeded;

+ unsigned int min_ratio;
+
struct device *dev;
};

@@ -136,6 +138,8 @@ static inline unsigned long bdi_stat_err
#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
Index: linux/mm/backing-dev.c
===================================================================
--- linux.orig/mm/backing-dev.c 2008-01-29 14:40:35.000000000 +0100
+++ linux/mm/backing-dev.c 2008-01-29 15:36:35.000000000 +0100
@@ -50,6 +50,24 @@ static inline unsigned long get_dirty(st
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[] = {
@@ -58,6 +76,7 @@ static struct device_attribute bdi_dev_a
__ATTR_RO(writeback_kb),
__ATTR_RO(dirty_kb),
__ATTR_RO(bdi_dirty_kb),
+ __ATTR_RW(min_ratio),
__ATTR_NULL,
};

@@ -116,6 +135,8 @@ int bdi_init(struct backing_dev_info *bd

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)
Index: linux/mm/page-writeback.c
===================================================================
--- linux.orig/mm/page-writeback.c 2008-01-29 14:40:35.000000000 +0100
+++ linux/mm/page-writeback.c 2008-01-29 15:35:34.000000000 +0100
@@ -247,6 +247,29 @@ static void task_dirty_limit(struct task
}

/*
+ *
+ */
+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.
*
@@ -334,7 +357,7 @@ get_dirty_limits(long *pbackground, long
*pdirty = dirty;

if (bdi) {
- u64 bdi_dirty = dirty;
+ u64 bdi_dirty;
long numerator, denominator;

/*
@@ -342,8 +365,10 @@ get_dirty_limits(long *pbackground, long
*/
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);
Index: linux/Documentation/ABI/testing/sysfs-class-bdi
===================================================================
--- linux.orig/Documentation/ABI/testing/sysfs-class-bdi 2008-01-29 14:40:35.000000000 +0100
+++ linux/Documentation/ABI/testing/sysfs-class-bdi 2008-01-29 15:37:24.000000000 +0100
@@ -48,3 +48,9 @@ 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
--


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