From: Paul E. McKenney Date: Thu, 19 Nov 2020 00:01:32 +0000 (-0800) Subject: srcu: Document polling interfaces for Tree SRCU grace periods X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ee7f4a87a18cd3bb141b38e2ef0c3e53253cdf63;p=linux.git srcu: Document polling interfaces for Tree SRCU grace periods This commit adds requirements documentation for the get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() functions. Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ Reported-by: Kent Overstreet Reviewed-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index e8c84fcc05071..93a189ae85924 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 ~~~~~~~~~