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>

1 files changed, 3 insertions, 1 deletions

diff --git a/init/Kconfig b/init/Kconfig
index a5e90e139ba5..fb19b46c0042 100644
--- 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