From patchwork Thu Aug 30 18:18:22 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 11043 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id B713323EFE for ; Thu, 30 Aug 2012 18:19:29 +0000 (UTC) Received: from mail-iy0-f180.google.com (mail-iy0-f180.google.com [209.85.210.180]) by fiordland.canonical.com (Postfix) with ESMTP id 722E9A1818E for ; Thu, 30 Aug 2012 18:18:53 +0000 (UTC) Received: by mail-iy0-f180.google.com with SMTP id j25so3403526iaf.11 for ; Thu, 30 Aug 2012 11:19:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-forwarded-to:x-forwarded-for:delivered-to:received-spf:from:to:cc :subject:date:message-id:x-mailer:in-reply-to:references :x-content-scanned:x-cbid:x-gm-message-state; bh=O4P3yGZPS4Ue7Sb/2gnQBX6PUg5Y+u1C5u3OpwnDTlo=; b=o26NuLXMjvNTsllXihuQsIMIpU6xiAFAFcoIAj/jnIgDyBl4XMwjsNL9+qqpRlcisj cPp5D2arglNnehhSTyx2s38buqe/bUvWY0rDn3JdoqmNXb1PjyzZ3PU1nHbKiDyvC/Zc IhjXz72deMQTHZg4+0btqIk0pgr9dPRMNQlgwcV3y46Qy6l264S/gDn2/RFTLtlViX73 txXQWs0OdLb2z7/5RrxVoz9Ws3AQteJwWiKa0BdN/d6HbRlYCqmuc5Nm/M+KY3vL9nLh DSwplPEqeFKlfe/ZI9TpBDSCOA+bxUWlLs6zZyet6wKhtvtutZM/5bMgw39iTWe195xt aVgw== Received: by 10.50.207.106 with SMTP id lv10mr1904404igc.0.1346350769088; Thu, 30 Aug 2012 11:19:29 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.50.184.232 with SMTP id ex8csp24713igc; Thu, 30 Aug 2012 11:19:28 -0700 (PDT) Received: by 10.60.30.132 with SMTP id s4mr5594410oeh.6.1346350768527; Thu, 30 Aug 2012 11:19:28 -0700 (PDT) Received: from e39.co.us.ibm.com (e39.co.us.ibm.com. [32.97.110.160]) by mx.google.com with ESMTPS id ks5si3088144obb.98.2012.08.30.11.19.28 (version=TLSv1/SSLv3 cipher=OTHER); Thu, 30 Aug 2012 11:19:28 -0700 (PDT) Received-SPF: pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.110.160 as permitted sender) client-ip=32.97.110.160; Authentication-Results: mx.google.com; spf=pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.110.160 as permitted sender) smtp.mail=paulmck@linux.vnet.ibm.com Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 30 Aug 2012 12:19:28 -0600 Received: from d03dlp03.boulder.ibm.com (9.17.202.179) by e39.co.us.ibm.com (192.168.1.139) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Thu, 30 Aug 2012 12:19:24 -0600 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 3656819D804A; Thu, 30 Aug 2012 12:19:23 -0600 (MDT) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q7UIJATM068848; Thu, 30 Aug 2012 12:19:11 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q7UIIhCS018845; Thu, 30 Aug 2012 12:18:51 -0600 Received: from paulmck-ThinkPad-W500 (sig-9-77-132-62.mts.ibm.com [9.77.132.62]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q7UIIgD4018686; Thu, 30 Aug 2012 12:18:42 -0600 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 22D65EA82C; Thu, 30 Aug 2012 11:18:40 -0700 (PDT) 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: 12083018-4242-0000-0000-000002B997DF X-Gm-Message-State: ALoCoQlKFyawooOkAmRQfoFB5j3sokaXCghmXqDC5aERvdeipJ5vq7PHwXcK2QBHf+LdlnqQpSgL 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 Reviewed-by: Josh Triplett --- 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