Commit 2450b78e authored by Zqiang's avatar Zqiang Committed by Joel Fernandes (Google)
Browse files

rcu: Register rcu-lazy shrinker only for CONFIG_RCU_LAZY=y kernels 



The lazy_rcu_shrink_count() shrinker function is registered even in
kernels built with CONFIG_RCU_LAZY=n, in which case this function
uselessly consumes cycles learning that no CPU has any lazy callbacks
queued.

This commit therefore registers this shrinker function only in the kernels
built with CONFIG_RCU_LAZY=y, where it might actually do something useful.

Signed-off-by: default avatarZqiang <qiang1.zhang@intel.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
parent db7b464d

kernel/rcu/tree_nocb.h

+4 −0
Original line number Diff line number Diff line
@@ -1312,6 +1312,7 @@ int rcu_nocb_cpu_offload(int cpu) 
}

EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);



#ifdef CONFIG_RCU_LAZY

static unsigned long

lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)

{
@@ -1360,6 +1361,7 @@ static struct shrinker lazy_rcu_shrinker = { 
	.batch = 0,

	.seeks = DEFAULT_SEEKS,

};

#endif // #ifdef CONFIG_RCU_LAZY



void __init rcu_init_nohz(void)

{
@@ -1391,8 +1393,10 @@ void __init rcu_init_nohz(void) 
	if (!rcu_state.nocb_is_setup)

		return;



#ifdef CONFIG_RCU_LAZY

	if (register_shrinker(&lazy_rcu_shrinker, "rcu-lazy"))

		pr_err("Failed to register lazy_rcu shrinker!\n");

#endif // #ifdef CONFIG_RCU_LAZY



	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {

		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");