From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754705Ab2H3STk (ORCPT ); Thu, 30 Aug 2012 14:19:40 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:51154 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752648Ab2H3STi (ORCPT ); Thu, 30 Aug 2012 14:19:38 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate lazy RCU callbacks Date: Thu, 30 Aug 2012 11:18:22 -0700 Message-Id: <1346350718-30937-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8 In-Reply-To: <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20120830181811.GA29154@linux.vnet.ibm.com> <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12083018-1780-0000-0000-000008DEB0DA X-IBM-ISS-SpamDetectors: X-IBM-ISS-DetailInfo: BY=3.00000293; HX=3.00000196; KW=3.00000007; PH=3.00000001; SC=3.00000007; SDB=6.00169857; UDB=6.00038508; UTC=2012-08-30 18:19:35 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" 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 non-lazy callbacks has at least one non-lazy callback, in turn ensuring timely advancement for these callbacks. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Sasha Levin --- kernel/rcutree.h | 5 ++- kernel/rcutree_plugin.h | 80 +++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+), 1 deletions(-) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 117a150..effb273 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; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7f3244c..bac8cc1 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,6 +25,7 @@ */ #include +#include #define RCU_KTHREAD_PRIO 1 @@ -2112,6 +2113,85 @@ static void rcu_idle_count_callbacks_posted(void) __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 *flavor) +{ + struct rcu_state *rsp = flavor; + struct rcu_data *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. + */ +static int rcu_oom_notify(struct notifier_block *self, + unsigned long notused, void *nfreed) +{ + int cpu; + struct rcu_state *rsp; + + /* 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) + for_each_rcu_flavor(rsp) + smp_call_function_single(cpu, rcu_oom_notify_cpu, + rsp, 1); + put_online_cpus(); + + /* Unconditionally decrement: no need to wake ourselves up. */ + atomic_dec(&oom_callback_count); + + *(unsigned long *)nfreed = 1; + 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) */ #ifdef CONFIG_RCU_CPU_STALL_INFO -- 1.7.8