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srcu: Document polling interfaces for Tree SRCU grace periods

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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 <kent.overstreet@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-11-18 16:01:32 -08:00
parent 5358c9fa54
commit ee7f4a87a1
1 changed files with 18 additions and 0 deletions
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Documentation/RCU/Design/Requirements/Requirements.rst
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@ -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
~~~~~~~~~