diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index e8c84fcc0507..93a189ae8592 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -2600,6 +2600,24 @@ also includes ``DEFINE_SRCU()``, ``DEFINE_STATIC_SRCU()``, and
 ``init_srcu_struct()`` APIs for defining and initializing
 ``srcu_struct`` structures.
 
+More recently, the SRCU API has added polling interfaces:
+
+#. start_poll_synchronize_srcu() returns a cookie identifying
+   the completion of a future SRCU grace period and ensures
+   that this grace period will be started.
+#. poll_state_synchronize_srcu() returns ``true`` iff the
+   specified cookie corresponds to an already-completed
+   SRCU grace period.
+#. get_state_synchronize_srcu() returns a cookie just like
+   start_poll_synchronize_srcu() does, but differs in that
+   it does nothing to ensure that any future SRCU grace period
+   will be started.
+
+These functions are used to avoid unnecessary SRCU grace periods in
+certain types of buffer-cache algorithms having multi-stage age-out
+mechanisms.  The idea is that by the time the block has aged completely
+from the cache, an SRCU grace period will be very likely to have elapsed.
+
 Tasks RCU
 ~~~~~~~~~