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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 ECA8AC47247 for ; Tue, 5 May 2020 17:28:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAF6B206E6 for ; Tue, 5 May 2020 17:28:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588699734; bh=0tg/+4uFrc4NuN9+XaScDh76eyqdHaQjaxnbXP2fh3M=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=N/nzdjzEXAjeAcvyfEy4QkreAiBK6lLXxiMcASxOq+Nh3Yv5CqF/XXWsoQZ4nYPWC kHTYvcNeGyef7zE5YmAC5+V285pyI+Khn7kVbavRtJh7gboaFBMP5f+zRPmcpGI48E lgwFIrp64Kt6ljJkTVoz2OvuX8yzu25zmP5MW0V4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730069AbgEER2w (ORCPT ); Tue, 5 May 2020 13:28:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:33472 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726350AbgEER2w (ORCPT ); Tue, 5 May 2020 13:28:52 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1C6D9206A4; Tue, 5 May 2020 17:28:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588699731; bh=0tg/+4uFrc4NuN9+XaScDh76eyqdHaQjaxnbXP2fh3M=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=HsdR6gXMlQz9DTbySEUZnv96Ssw8gwFHsnjXhl5n41r3XsNos7ePFU7PaeB8cC06z vKtXku2yXZVkTNnShdzrDN32zETRTJDDsy59ylUZHDadRmA91ZhCCDWzf23/okw21g qzojrmYp1rnHMIVe2SigXCIOxZeQQ2m7ywYhfU6I= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id F00643522F5F; Tue, 5 May 2020 10:28:50 -0700 (PDT) Date: Tue, 5 May 2020 10:28:50 -0700 From: "Paul E. McKenney" To: Eric Dumazet Cc: SeongJae Park , Eric Dumazet , David Miller , Al Viro , Jakub Kicinski , Greg Kroah-Hartman , sj38.park@gmail.com, netdev , LKML , SeongJae Park , snu@amazon.com, amit@kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change Message-ID: <20200505172850.GD2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200505161302.547-1-sjpark@amazon.com> <05843a3c-eb9d-3a0d-f992-7e4b97cc1f19@gmail.com> <77124fc2-86b2-27f6-fd7c-4f1e86eb3fff@gmail.com> <67bdfac9-0d7d-0bbe-dc7a-d73979fd8ed9@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <67bdfac9-0d7d-0bbe-dc7a-d73979fd8ed9@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, May 05, 2020 at 09:37:42AM -0700, Eric Dumazet wrote: > > > On 5/5/20 9:31 AM, Eric Dumazet wrote: > > > > > > On 5/5/20 9:25 AM, Eric Dumazet wrote: > >> > >> > >> On 5/5/20 9:13 AM, SeongJae Park wrote: > >>> On Tue, 5 May 2020 09:00:44 -0700 Eric Dumazet wrote: > >>> > >>>> On Tue, May 5, 2020 at 8:47 AM SeongJae Park wrote: > >>>>> > >>>>> On Tue, 5 May 2020 08:20:50 -0700 Eric Dumazet wrote: > >>>>> > >>>>>> > >>>>>> > >>>>>> On 5/5/20 8:07 AM, SeongJae Park wrote: > >>>>>>> On Tue, 5 May 2020 07:53:39 -0700 Eric Dumazet wrote: > >>>>>>> > >>>>>> > >>>>>>>> Why do we have 10,000,000 objects around ? Could this be because of > >>>>>>>> some RCU problem ? > >>>>>>> > >>>>>>> Mainly because of a long RCU grace period, as you guess. I have no idea how > >>>>>>> the grace period became so long in this case. > >>>>>>> > >>>>>>> As my test machine was a virtual machine instance, I guess RCU readers > >>>>>>> preemption[1] like problem might affected this. > >>>>>>> > >>>>>>> [1] https://www.usenix.org/system/files/conference/atc17/atc17-prasad.pdf > >>>>>>> > >>>>>>>> > >>>>>>>> Once Al patches reverted, do you have 10,000,000 sock_alloc around ? > >>>>>>> > >>>>>>> Yes, both the old kernel that prior to Al's patches and the recent kernel > >>>>>>> reverting the Al's patches didn't reproduce the problem. > >>>>>>> > >>>>>> > >>>>>> I repeat my question : Do you have 10,000,000 (smaller) objects kept in slab caches ? > >>>>>> > >>>>>> TCP sockets use the (very complex, error prone) SLAB_TYPESAFE_BY_RCU, but not the struct socket_wq > >>>>>> object that was allocated in sock_alloc_inode() before Al patches. > >>>>>> > >>>>>> These objects should be visible in kmalloc-64 kmem cache. > >>>>> > >>>>> Not exactly the 10,000,000, as it is only the possible highest number, but I > >>>>> was able to observe clear exponential increase of the number of the objects > >>>>> using slabtop. Before the start of the problematic workload, the number of > >>>>> objects of 'kmalloc-64' was 5760, but I was able to observe the number increase > >>>>> to 1,136,576. > >>>>> > >>>>> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > >>>>> before: 5760 5088 88% 0.06K 90 64 360K kmalloc-64 > >>>>> after: 1136576 1136576 100% 0.06K 17759 64 71036K kmalloc-64 > >>>>> > >>>> > >>>> Great, thanks. > >>>> > >>>> How recent is the kernel you are running for your experiment ? > >>> > >>> It's based on 5.4.35. > >>> > >>>> > >>>> Let's make sure the bug is not in RCU. > >>> > >>> One thing I can currently say is that the grace period passes at last. I > >>> modified the benchmark to repeat not 10,000 times but only 5,000 times to run > >>> the test without OOM but easily observable memory pressure. As soon as the > >>> benchmark finishes, the memory were freed. > >>> > >>> If you need more tests, please let me know. > >>> > >> > >> I would ask Paul opinion on this issue, because we have many objects > >> being freed after RCU grace periods. > >> > >> If RCU subsystem can not keep-up, I guess other workloads will also suffer. > >> > >> Sure, we can revert patches there and there trying to work around the issue, > >> but for objects allocated from process context, we should not have these problems. > >> > > > > I wonder if simply adjusting rcu_divisor to 6 or 5 would help > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index d9a49cd6065a20936edbda1b334136ab597cde52..fde833bac0f9f81e8536211b4dad6e7575c1219a 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -427,7 +427,7 @@ module_param(qovld, long, 0444); > > static ulong jiffies_till_first_fqs = ULONG_MAX; > > static ulong jiffies_till_next_fqs = ULONG_MAX; > > static bool rcu_kick_kthreads; > > -static int rcu_divisor = 7; > > +static int rcu_divisor = 6; > > module_param(rcu_divisor, int, 0644); > > > > /* Force an exit from rcu_do_batch() after 3 milliseconds. */ > > > > To be clear, you can adjust the value without building a new kernel. > > echo 6 >/sys/module/rcutree/parameters/rcu_divisor Worth a try! If that helps significantly, I have some ideas for updating that heuristic, such as checking for sudden increases in the number of pending callbacks. But I would really also like to know whether there are long readers and whether v5.6 fares better. Thanx, Paul