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mm: add /sys/class/bdi/<bdi>/min_bytes knob
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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/[email protected]
Signed-off-by: Stefan Roesch <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
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Stefan Roesch authored and akpm00 committed Nov 30, 2022
1 parent 803c980 commit 9c84819
Showing 1 changed file with 29 additions and 0 deletions.
29 changes: 29 additions & 0 deletions mm/backing-dev.c
Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down Expand Up @@ -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,
Expand Down

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