rcu: Provide OOM handler to motivate lazy RCU callbacks (b626c1b6) · Commits · 戴 / test

kernel/rcutree.h

+4 −1

Original line number	Original line	Diff line number	Diff line
	@@ -315,8 +315,11 @@ struct rcu_data {
	unsigned long n_rp_need_fqs;		unsigned long n_rp_need_fqs;
	unsigned long n_rp_need_nothing;		unsigned long n_rp_need_nothing;

	/* 6) _rcu_barrier() callback. */		/* 6) _rcu_barrier() and OOM callbacks. */
	struct rcu_head barrier_head;		struct rcu_head barrier_head;
			#ifdef CONFIG_RCU_FAST_NO_HZ
			struct rcu_head oom_head;
			#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */

	int cpu;		int cpu;
	struct rcu_state *rsp;		struct rcu_state *rsp;

kernel/rcutree_plugin.h

+83 −0

Original line number	Original line	Diff line number	Diff line
	@@ -25,6 +25,7 @@
	*/		*/

	#include <linux/delay.h>		#include <linux/delay.h>
			#include <linux/oom.h>

	#define RCU_KTHREAD_PRIO 1		#define RCU_KTHREAD_PRIO 1

	@@ -2112,6 +2113,88 @@ static void rcu_idle_count_callbacks_posted(void)
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);		__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
	}		}

			/*
			* Data for flushing lazy RCU callbacks at OOM time.
			*/
			static atomic_t oom_callback_count;
			static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);

			/*
			* RCU OOM callback -- decrement the outstanding count and deliver the
			* wake-up if we are the last one.
			*/
			static void rcu_oom_callback(struct rcu_head *rhp)
			{
			if (atomic_dec_and_test(&oom_callback_count))
			wake_up(&oom_callback_wq);
			}

			/*
			* Post an rcu_oom_notify callback on the current CPU if it has at
			* least one lazy callback. This will unnecessarily post callbacks
			* to CPUs that already have a non-lazy callback at the end of their
			* callback list, but this is an infrequent operation, so accept some
			* extra overhead to keep things simple.
			*/
			static void rcu_oom_notify_cpu(void *unused)
			{
			struct rcu_state *rsp;
			struct rcu_data *rdp;

			for_each_rcu_flavor(rsp) {
			rdp = __this_cpu_ptr(rsp->rda);
			if (rdp->qlen_lazy != 0) {
			atomic_inc(&oom_callback_count);
			rsp->call(&rdp->oom_head, rcu_oom_callback);
			}
			}
			}

			/*
			* If low on memory, ensure that each CPU has a non-lazy callback.
			* This will wake up CPUs that have only lazy callbacks, in turn
			* ensuring that they free up the corresponding memory in a timely manner.
			* Because an uncertain amount of memory will be freed in some uncertain
			* timeframe, we do not claim to have freed anything.
			*/
			static int rcu_oom_notify(struct notifier_block *self,
			unsigned long notused, void *nfreed)
			{
			int cpu;

			/* Wait for callbacks from earlier instance to complete. */
			wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);

			/*
			* Prevent premature wakeup: ensure that all increments happen
			* before there is a chance of the counter reaching zero.
			*/
			atomic_set(&oom_callback_count, 1);

			get_online_cpus();
			for_each_online_cpu(cpu) {
			smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
			cond_resched();
			}
			put_online_cpus();

			/* Unconditionally decrement: no need to wake ourselves up. */
			atomic_dec(&oom_callback_count);

			return NOTIFY_OK;
			}

			static struct notifier_block rcu_oom_nb = {
			.notifier_call = rcu_oom_notify
			};

			static int __init rcu_register_oom_notifier(void)
			{
			register_oom_notifier(&rcu_oom_nb);
			return 0;
			}
			early_initcall(rcu_register_oom_notifier);

	#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */		#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */

	#ifdef CONFIG_RCU_CPU_STALL_INFO		#ifdef CONFIG_RCU_CPU_STALL_INFO

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