Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754051AbbLJXbV (ORCPT ); Thu, 10 Dec 2015 18:31:21 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:47753 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751222AbbLJXbT (ORCPT ); Thu, 10 Dec 2015 18:31:19 -0500 Date: Thu, 10 Dec 2015 15:31:18 -0800 From: Andrew Morton To: Christoph Lameter Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, penguin-kernel@I-love.SAKURA.ne.jp Subject: Re: vmstat: make vmstat_updater deferrable again and shut down on idle Message-Id: <20151210153118.4f39d6a4f04c96189ce015c9@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1654 Lines: 43 On Thu, 10 Dec 2015 14:45:02 -0600 (CST) Christoph Lameter wrote: > Currently the vmstat updater is not deferrable as a result of commit > ba4877b9ca51f80b5d30f304a46762f0509e1635. This in turn can cause multiple > interruptions of the applications because the vmstat updater may run at > different times than tick processing. No good. > > Make vmstate_update deferrable again and provide a function that > folds the differentials when the processor is going to idle mode thus > addressing the issue of the above commit in a clean way. > > Note that the shepherd thread will continue scanning the differentials > from another processor and will reenable the vmstat workers if it > detects any changes. > > Fixes: ba4877b9ca51f80b5d30f304a46762f0509e1635 (do not use deferrable delay) > Signed-off-by: Christoph Lameter > > ... > > /* > + * Switch off vmstat processing and then fold all the remaining differentials > + * until the diffs stay at zero. The function is used by NOHZ and can only be > + * invoked when tick processing is not active. > + */ > +void quiet_vmstat(void) > +{ > + do { > + if (!cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off)) > + cancel_delayed_work(this_cpu_ptr(&vmstat_work)); > + > + } while (refresh_cpu_vm_stats(false)); > +} How do we know this will terminate in a reasonable amount of time if other CPUs are pounding away? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/