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mm: add /sys/class/bdi/<bdi>/min_bytes knob 

bdi has two existing knobs to limit the amount of dirty memory:
min_ratio and max_ratio. However the granularity of the knobs is limited
and often it is more convenient to specify limits in terms of bytes.
This change adds the min_bytes knob.

It does not store the min_bytes value, instead it converts the max_bytes
value to a ratio. The value is therefore more an approximation than an
absolute value.

It also maintains the sum over all the bdi min_ratio values stored in
the variable bdi_min_ratio.

Link: https://lkml.kernel.org/r/20221119005215.3052436-14-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Cc: Chris Mason <clm@meta.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Stefan Roesch 2022-11-18 16:52:08 -08:00 committed by Andrew Morton
parent 803c980505
commit 9c84819bd6
1 changed files with 29 additions and 0 deletions
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29
mm/backing-dev.c
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@ -199,6 +199,34 @@ static ssize_t max_ratio_store(struct device *dev,
}
BDI_SHOW(max_ratio, bdi->max_ratio / BDI_RATIO_SCALE)
static ssize_t min_bytes_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct backing_dev_info *bdi = dev_get_drvdata(dev);
return sysfs_emit(buf, "%llu\n", bdi_get_min_bytes(bdi));
}
static ssize_t min_bytes_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
struct backing_dev_info *bdi = dev_get_drvdata(dev);
u64 bytes;
ssize_t ret;
ret = kstrtoull(buf, 10, &bytes);
if (ret < 0)
return ret;
ret = bdi_set_min_bytes(bdi, bytes);
if (!ret)
ret = count;
return ret;
}
DEVICE_ATTR_RW(min_bytes);
static ssize_t max_bytes_show(struct device *dev,
struct device_attribute *attr,
char *buf)
@ -269,6 +297,7 @@ static struct attribute *bdi_dev_attrs[] = {
&dev_attr_read_ahead_kb.attr,
&dev_attr_min_ratio.attr,
&dev_attr_max_ratio.attr,
&dev_attr_min_bytes.attr,
&dev_attr_max_bytes.attr,
&dev_attr_stable_pages_required.attr,
&dev_attr_strict_limit.attr,