summaryrefslogtreecommitdiffstats
path: root/Documentation/ABI/testing/sysfs-class-bdi
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/ABI/testing/sysfs-class-bdi')
-rw-r--r--Documentation/ABI/testing/sysfs-class-bdi46
1 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
new file mode 100644
index 00000000000..5ac1e01bbd4
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -0,0 +1,46 @@
+What: /sys/class/bdi/<bdi>/
+Date: January 2008
+Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
+Description:
+
+Provide a place in sysfs for the backing_dev_info object. This allows
+setting and retrieving various BDI specific variables.
+
+The <bdi> identifier can be either of the following:
+
+MAJOR:MINOR
+
+ Device number for block devices, or value of st_dev on
+ non-block filesystems which provide their own BDI, such as NFS
+ and FUSE.
+
+default
+
+ The default backing dev, used for non-block device backed
+ filesystems which do not provide their own BDI.
+
+Files under /sys/class/bdi/<bdi>/
+---------------------------------
+
+read_ahead_kb (read-write)
+
+ Size of the read-ahead window in kilobytes
+
+min_ratio (read-write)
+
+ Under normal circumstances each device is given a part of the
+ total write-back cache that relates to its current average
+ writeout speed in relation to the other devices.
+
+ The 'min_ratio' parameter allows assigning a minimum
+ percentage of the write-back cache to a particular device.
+ For example, this is useful for providing a minimum QoS.
+
+max_ratio (read-write)
+
+ Allows limiting a particular device to use not more than the
+ given percentage of the write-back cache. This is useful in
+ situations where we want to avoid one device taking all or
+ most of the write-back cache. For example in case of an NFS
+ mount that is prone to get stuck, or a FUSE mount which cannot
+ be trusted to play fair.