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Subject[PATCH tip/core/rcu 2/2] rcu: Allow TREE_PREEMPT_RCU on UP systems
From: "Paul E. McKenney" <>

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

Signed-off-by: Paul E. McKenney <>
init/Kconfig | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index a5e90e1..fb19b46 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -453,7 +453,7 @@ config TREE_RCU

bool "Preemptible tree-based hierarchical RCU"
- depends on PREEMPT && SMP
+ depends on PREEMPT
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

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