[RFC PATCH v4 17/20] mm: document /sys/class/bdi/<bdi>/max_ratio_fine knob

[Stefan Roesch <shr@devkernel.io>]

This documents the new /sys/class/bdi/<bdi>/max_ratio_fine knob.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 Documentation/ABI/testing/sysfs-class-bdi | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index bec996e29565..34d2e5489c74 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -57,6 +57,19 @@ Description:
 
 	(read-write)
 
+What:		/sys/class/bdi/<bdi>/max_ratio_fine
+Date:		November 2022
+Contact:	Stefan Roesch <shr@devkernel.io>
+Description:
+	Allows limiting a particular device to use not more than the
+	given value of the write-back cache.  The value is given as part
+    of 1 million. 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.
+
+	(read-write)
+
 What:		/sys/class/bdi/<bdi>/min_bytes
 Date:		October 2022
 Contact:	Stefan Roesch <shr@devkernel.io>
-- 
2.30.2