mm: document /sys/class/bdi/<bdi>/min_ratio_fine knob

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

[akpm@linux-foundation.org: fix htmldocs warnings]
Link: https://lkml.kernel.org/r/20221119005215.3052436-21-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Cc: Chris Mason <clm@meta.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index e9c584d..0d2abd8 100644 (file)
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -44,6 +44,21 @@ Description:
 
        (read-write)
 
+What:          /sys/class/bdi/<bdi>/min_ratio_fine
+Date:          November 2022
+Contact:       Stefan Roesch <shr@devkernel.io>
+Description:
+       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_fine' parameter allows assigning a minimum reserve
+       of the write-back cache to a particular device. The value is
+       expressed as part of 1 million. For example, this is useful for
+       providing a minimum QoS.
+
+       (read-write)
+
 What:          /sys/class/bdi/<bdi>/max_ratio
 Date:          January 2008
 Contact:       Peter Zijlstra <a.p.zijlstra@chello.nl>