Commit b17c7035 authored Sep 06, 2012 by Paul E. McKenney

rcu: Shrink RCU based on number of CPUs



Currently, rcu_init_geometry() only reshapes RCU's combining trees
if the leaf fanout is changed at boot time.  This means that by
default, kernels compiled with (say) NR_CPUS=4096 will keep oversized
data structures, even when running on systems with (say) four CPUs.

This commit therefore checks to see if the maximum number of CPUs on
the actual running system (nr_cpu_ids) differs from NR_CPUS, and if so
reshapes the combining trees accordingly.

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 4dbd6bb3

kernel/rcutree.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2821,7 +2821,8 @@ static void __init rcu_init_geometry(void)
		int rcu_capacity[MAX_RCU_LVLS + 1];

		/* If the compile-time values are accurate, just leave. */
		if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF)
		if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
		nr_cpu_ids == NR_CPUS)
		return;

		/*