Commit 9c84819b authored by Stefan Roesch's avatar Stefan Roesch Committed by Andrew Morton
Browse files

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: default avatarStefan Roesch <shr@devkernel.io>
Cc: Chris Mason <clm@meta.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 803c9805

mm/backing-dev.c

+29 −0
Original line number Diff line number Diff line
@@ -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,