From b626c1b689364859ccd2e86d5e043aeadfeb2cd4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 11 Jun 2012 17:39:43 -0700 Subject: rcu: Provide OOM handler to motivate lazy RCU callbacks In kernels built with CONFIG_RCU_FAST_NO_HZ=y, CPUs can accumulate a large number of lazy callbacks, which as the name implies will be slow to be invoked. This can be a problem on small-memory systems, where the default 6-second sleep for CPUs having only lazy RCU callbacks could well be fatal. This commit therefore installs an OOM hander that ensures that every CPU with lazy callbacks has at least one non-lazy callback, in turn ensuring timely advancement for these callbacks. Updated to fix bug that disabled OOM killing, noted by Lai Jiangshan. Updated to push the for_each_rcu_flavor() loop into rcu_oom_notify_cpu(), thus reducing the number of IPIs, as suggested by Steven Rostedt. Also to make the for_each_online_cpu() loop be preemptible. (Later, it might be good to use smp_call_function(), as suggested by Peter Zijlstra.) Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Sasha Levin Reviewed-by: Josh Triplett --- kernel/rcutree.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/rcutree.h') diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 117a15019e99..effb2733b7fc 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -315,8 +315,11 @@ struct rcu_data { unsigned long n_rp_need_fqs; unsigned long n_rp_need_nothing; - /* 6) _rcu_barrier() callback. */ + /* 6) _rcu_barrier() and OOM callbacks. */ 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; struct rcu_state *rsp; -- cgit v1.2.3