From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6902C433FF for ; Fri, 9 Aug 2019 20:26:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BBC5214C6 for ; Fri, 9 Aug 2019 20:26:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="HYxy1KIX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726053AbfHIU0t (ORCPT ); Fri, 9 Aug 2019 16:26:49 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:40000 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725980AbfHIU0s (ORCPT ); Fri, 9 Aug 2019 16:26:48 -0400 Received: by mail-pf1-f195.google.com with SMTP id p184so46615595pfp.7 for ; Fri, 09 Aug 2019 13:26:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=xOuW1vgX9GzFRp2BRQ/iIfg703Hr+CMx7KleXDC/WG4=; b=HYxy1KIX9AuqfYtuDEcK2vFQoVptOaJM58zzimG166ZRrQaEFEojoAYysKO/VsTDrh MqlcfLIELyedo0vYqOdQC/mYWTZwklODssnIqVaGJZix716kdil2q8mwtxz6HM6o5Lq2 T7Is3OfxzNcKg8aO4oPDsFaLmt9QMk+8wnAPU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=xOuW1vgX9GzFRp2BRQ/iIfg703Hr+CMx7KleXDC/WG4=; b=cakkBmpbx1nL8fPGQIhqlsMWLbfh1K6RiDS1+MYt80jcQN75oZBboYvcEgRFkcX0w4 y6Co9Xj8PDWeEJrV81Su1LXotqiBoJhS8HEiliUCsxNHI5AzW1EM5iiqXYm3VXQ+kZZx FlofB8w7i3Ftfy2GFt2em2mQLoVTrrDfCTFt9udkHzykcUvRQ3F1Kj2xadyDSs5BjpMi UvTTaK+ABdrWYyezchOAbbp5z8nBwmeidE3RBF05qaNYE1182am3it2r2YiiXGyE05XW cBNUMH1JAdaRydcUqSEjiwFi6M2EnlZ80E5KBDW8LLXICKHVm61KSyBe3dQxWTf+1DS8 qFpQ== X-Gm-Message-State: APjAAAV569QFQlre2vVuX5bDz2ZurdrXe4HyHgoGx5gQjVhvTo2cU5/z nY/kKsccqE88YN/nFYgvnvvWMA== X-Google-Smtp-Source: APXvYqxMFNtQ4nA4/C5aiCp3MykTBQtEBdXrVMvA9Oy0yBPLQQVU2L/dsI00+DZBW/BXrZ5W2n6f7Q== X-Received: by 2002:a62:1941:: with SMTP id 62mr6792441pfz.188.1565382407972; Fri, 09 Aug 2019 13:26:47 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id v14sm21317794pgi.79.2019.08.09.13.26.46 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 09 Aug 2019 13:26:46 -0700 (PDT) Date: Fri, 9 Aug 2019 16:26:45 -0400 From: Joel Fernandes To: "Paul E. McKenney" Cc: Byungchul Park , linux-kernel@vger.kernel.org, Rao Shoaib , max.byungchul.park@gmail.com, Davidlohr Bueso , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching Message-ID: <20190809202645.GD255533@google.com> References: <20190806235631.GU28441@linux.ibm.com> <20190807094504.GB169551@google.com> <20190807175215.GE28441@linux.ibm.com> <20190808095232.GA30401@X58A-UD3R> <20190808125607.GB261256@google.com> <20190808233014.GA184373@google.com> <20190809151619.GD28441@linux.ibm.com> <20190809153924.GB211412@google.com> <20190809163346.GF28441@linux.ibm.com> <20190809202226.GC255533@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190809202226.GC255533@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Aug 09, 2019 at 04:22:26PM -0400, Joel Fernandes wrote: > On Fri, Aug 09, 2019 at 09:33:46AM -0700, Paul E. McKenney wrote: > > On Fri, Aug 09, 2019 at 11:39:24AM -0400, Joel Fernandes wrote: > > > On Fri, Aug 09, 2019 at 08:16:19AM -0700, Paul E. McKenney wrote: > > > > On Thu, Aug 08, 2019 at 07:30:14PM -0400, Joel Fernandes wrote: > > > [snip] > > > > > > But I could make it something like: > > > > > > 1. Letting ->head grow if ->head_free busy > > > > > > 2. If head_free is busy, then just queue/requeue the monitor to try again. > > > > > > > > > > > > This would even improve performance, but will still risk going out of memory. > > > > > > > > > > It seems I can indeed hit an out of memory condition once I changed it to > > > > > "letting list grow" (diff is below which applies on top of this patch) while > > > > > at the same time removing the schedule_timeout(2) and replacing it with > > > > > cond_resched() in the rcuperf test. I think the reason is the rcuperf test > > > > > starves the worker threads that are executing in workqueue context after a > > > > > grace period and those are unable to get enough CPU time to kfree things fast > > > > > enough. But I am not fully sure about it and need to test/trace more to > > > > > figure out why this is happening. > > > > > > > > > > If I add back the schedule_uninterruptibe_timeout(2) call, the out of memory > > > > > situation goes away. > > > > > > > > > > Clearly we need to do more work on this patch. > > > > > > > > > > In the regular kfree_rcu_no_batch() case, I don't hit this issue. I believe > > > > > that since the kfree is happening in softirq context in the _no_batch() case, > > > > > it fares better. The question then I guess is how do we run the rcu_work in a > > > > > higher priority context so it is not starved and runs often enough. I'll > > > > > trace more. > > > > > > > > > > Perhaps I can also lower the priority of the rcuperf threads to give the > > > > > worker thread some more room to run and see if anything changes. But I am not > > > > > sure then if we're preparing the code for the real world with such > > > > > modifications. > > > > > > > > > > Any thoughts? > > > > > > > > Several! With luck, perhaps some are useful. ;-) > > > > > > > > o Increase the memory via kvm.sh "--memory 1G" or more. The > > > > default is "--memory 500M". > > > > > > Thanks, this definitely helped. > > Also, I can go back to 500M if I just keep KFREE_DRAIN_JIFFIES at HZ/50. So I > am quite happy about that. I think I can declare that the "let list grow > indefinitely" design works quite well even with an insanely heavily loaded > case of every CPU in a 16CPU system with 500M memory, indefinitely doing > kfree_rcu()in a tight loop with appropriate cond_resched(). And I am like > thinking - wow how does this stuff even work at such insane scales :-D Oh, and I should probably also count whether there are any 'total number of grace periods' reduction, due to the batching! thanks, - Joel