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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 4B2B2C3A5A7 for ; Wed, 4 Sep 2019 08:25:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2258422CED for ; Wed, 4 Sep 2019 08:25:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567585544; bh=3MXsX1wNTs81EHNS5ZGFUn1k6ztTJrUiZrlXFBvlQQA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=gQhrlNYCv70LcmZFv4zgL0+NmxB63pGbQdeaceX3aLmeyOMmOIKg9awnw7bsiUVuR K3tgJ3hxavb8S9fxGT1jfNNvbcO3GrS81IqKX5tREbfJNFYoEzQf8IcfW2OyvCsQ32 7k0SPrsEbhPx/oLDw2O93gQU3heC1Mg63BvWNlQM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729522AbfIDIZn (ORCPT ); Wed, 4 Sep 2019 04:25:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:41322 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726358AbfIDIZm (ORCPT ); Wed, 4 Sep 2019 04:25:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6FFC6AE89; Wed, 4 Sep 2019 08:25:41 +0000 (UTC) Date: Wed, 4 Sep 2019 10:25:40 +0200 From: Michal Hocko To: Sergey Senozhatsky Cc: Qian Cai , Eric Dumazet , davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Petr Mladek , Sergey Senozhatsky , Steven Rostedt Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure Message-ID: <20190904082540.GI3838@dhcp22.suse.cz> References: <6109dab4-4061-8fee-96ac-320adf94e130@gmail.com> <1567178728.5576.32.camel@lca.pw> <229ebc3b-1c7e-474f-36f9-0fa603b889fb@gmail.com> <20190903132231.GC18939@dhcp22.suse.cz> <1567525342.5576.60.camel@lca.pw> <20190903185305.GA14028@dhcp22.suse.cz> <1567546948.5576.68.camel@lca.pw> <20190904061501.GB3838@dhcp22.suse.cz> <20190904064144.GA5487@jagdpanzerIV> <20190904070042.GA11968@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904070042.GA11968@jagdpanzerIV> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 04-09-19 16:00:42, Sergey Senozhatsky wrote: > On (09/04/19 15:41), Sergey Senozhatsky wrote: > > But the thing is different in case of dump_stack() + show_mem() + > > some other output. Because now we ratelimit not a single printk() line, > > but hundreds of them. The ratelimit becomes - 10 * $$$ lines in 5 seconds > > (IOW, now we talk about thousands of lines). > > And on devices with slow serial consoles this can be somewhat close to > "no ratelimit". *Suppose* that warn_alloc() adds 700 lines each time. > Within 5 seconds we can call warn_alloc() 10 times, which will add 7000 > lines to the logbuf. If printk() can evict only 6000 lines in 5 seconds > then we have a growing number of pending logbuf messages. Yes, ratelimit is problematic when the ratelimited operation is slow. I guess that is a well known problem and we would need to rework both the api and the implementation to make it work in those cases as well. Essentially we need to make the ratelimit act as a gatekeeper to an operation section - something like a critical section except you can tolerate more code executions but not too many. So effectively start_throttle(rate, number); /* here goes your operation */ end_throttle(); one operation is not considered done until the whole section ends. Or something along those lines. In this particular case we can increase the rate limit parameters of course but I think that longterm we need a better api. -- Michal Hocko SUSE Labs