rcu: Allow TREE_PREEMPT_RCU on UP systems

The TINY_PREEMPT_RCU is complex, does not provide that much memory
savings, and therefore TREE_PREEMPT_RCU should be used instead.  The
systems where the difference between TINY_PREEMPT_RCU and TREE_PREEMPT_RCU
are quite small compared to the memory footprint of CONFIG_PREEMPT.

This commit therefore takes a first step towards eliminating
TINY_PREEMPT_RCU by allowing TREE_PREEMPT_RCU to be configured on !SMP
systems.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/init/Kconfig b/init/Kconfig
index a5e90e1..fb19b46 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -453,7 +453,7 @@ config TREE_RCU
 
 config TREE_PREEMPT_RCU
        bool "Preemptible tree-based hierarchical RCU"
-       depends on PREEMPT && SMP
+       depends on PREEMPT
        help
          This option selects the RCU implementation that is
          designed for very large SMP systems with hundreds or
@@ -461,6 +461,8 @@ config TREE_PREEMPT_RCU
          is also required.  It also scales down nicely to
          smaller systems.
 
+         Select this option if you are unsure.
+
 config TINY_RCU
        bool "UP-only small-memory-footprint RCU"
        depends on !PREEMPT && !SMP