[RFC PATCH v3 08/14] mm: add knob /sys/class/bdi/<bdi>/max_bytes

[Stefan Roesch <shr@devkernel.io>]

This adds the new knob max_bytes to specify a dirty memory limit for the
corresponding bdi. The specified bytes value is converted to a ratio.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/backing-dev.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 90fa517123dc..d5f9a8a45550 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -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 max_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_max_bytes(bdi));
+}
+
+static ssize_t max_bytes_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+	unsigned long long bytes;
+	ssize_t ret;
+
+	ret = kstrtoull(buf, 10, &bytes);
+	if (ret < 0)
+		return ret;
+
+	ret = bdi_set_max_bytes(bdi, bytes);
+	if (!ret)
+		ret = count;
+
+	return ret;
+}
+DEVICE_ATTR_RW(max_bytes);
+
 static ssize_t stable_pages_required_show(struct device *dev,
 					  struct device_attribute *attr,
 					  char *buf)
@@ -241,6 +269,7 @@ static struct attribute *bdi_dev_attrs[] = {
 	&dev_attr_read_ahead_kb.attr,
 	&dev_attr_min_ratio.attr,
 	&dev_attr_max_ratio.attr,
+	&dev_attr_max_bytes.attr,
 	&dev_attr_stable_pages_required.attr,
 	&dev_attr_strict_limit.attr,
 	NULL,
-- 
2.30.2