[RFC PATCH v2 5/5] docs: cgroup-v2: document io.cost model=<name> binding

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

Document the named-model binding of io.cost.model in the
io.cost.model section of the cgroup v2 documentation: the binding
and restore syntax, the unknown-name rejection, the full-replacement
semantics of a bound model and the unregister lifetime.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 Documentation/admin-guide/cgroup-v2.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 8d2603751c51..a6910ad7c2d0 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2124,6 +2124,17 @@ IO Interface Files
 	parameters are written to, "ctrl" become "user" and the
 	automatic changes are disabled.
 
+	When CONFIG_BLK_CGROUP_IOCOST_BPF is enabled, "model" also accepts
+	the name of a registered iocost_model_ops BPF struct_ops model:
+	"model=<name>" binds the model to the device and the model fully
+	replaces the builtin linear pricing, for every operation including
+	flushes; "model=linear" (or "ctrl=auto/user") restores the builtin
+	model.  Writing an unknown name fails with ENOENT.  Unregistering
+	a model removes its name; devices already bound keep using it
+	until switched back to the builtin model, following the lifetime
+	model of TCP congestion control.  See include/linux/blk-iocost.h
+	for the model interface.
+
 	When "model" is "linear", the following model parameters are
 	defined.
 
-- 
2.43.0