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

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

Link: https://lkml.kernel.org/r/20221119005215.3052436-4-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 6d2a2fc..68b5d40 100644 (file)
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -56,6 +56,17 @@ Description:
        be trusted to play fair.
 
        (read-write)
+What:          /sys/class/bdi/<bdi>/strict_limit
+Date:          October 2022
+Contact:       Stefan Roesch <shr@devkernel.io>
+Description:
+       Forces per-BDI checks for the share of given device in the write-back
+       cache even before the global background dirty limit is reached. This
+       is useful in situations where the global limit is much higher than
+       affordable for given relatively slow (or untrusted) device. Turning
+       strictlimit on has no visible effect if max_ratio is equal to 100%.
+
+       (read-write)
 What:          /sys/class/bdi/<bdi>/stable_pages_required
 Date:          January 2008
 Contact:       Peter Zijlstra <a.p.zijlstra@chello.nl>