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 B53E5C41514 for ; Wed, 4 Sep 2019 12:07:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E8002339E for ; Wed, 4 Sep 2019 12:07:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567598830; bh=HmJDD7dX1w2sXcAZ6BVqVp/dRNXg/8OjfveY9uKhejk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=lTWPR1UGr5Z8o0Aer7zhOVtjAE7ltgIS0DFMIQM6Y//n8O5k4MAYMCKXJVmOCeFj2 O2mZzU1JRYbzmnH+kU74QKBSHdfHZFyeEbgfa4D0Il0MLquu6Jm7l7PcAC9S4RrPNw rrU4DTrtb3gkjmB2S4ZEdJBO6OOFJRb8dtW4T9Hc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729864AbfIDMHJ (ORCPT ); Wed, 4 Sep 2019 08:07:09 -0400 Received: from mx2.suse.de ([195.135.220.15]:33924 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729316AbfIDMHJ (ORCPT ); Wed, 4 Sep 2019 08:07:09 -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 AA79EB66A; Wed, 4 Sep 2019 12:07:07 +0000 (UTC) Date: Wed, 4 Sep 2019 14:07:07 +0200 From: Michal Hocko To: Qian Cai Cc: Sergey Senozhatsky , 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: <20190904120707.GU3838@dhcp22.suse.cz> References: <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> <20190904082540.GI3838@dhcp22.suse.cz> <1567598357.5576.70.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1567598357.5576.70.camel@lca.pw> 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 07:59:17, Qian Cai wrote: > On Wed, 2019-09-04 at 10:25 +0200, Michal Hocko wrote: > > 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. > > The problem is when a system is under heavy memory pressure, everything is > becoming slower, so I don't know how to come up with a sane default for rate > limit parameters as a generic solution that would work for every machine out > there. Sure, it is possible to set a limit as low as possible that would work > for the majority of systems apart from people may complain that they are now > missing important warnings, but using __GFP_NOWARN in this code would work for > all systems. You could even argument there is even a separate benefit that it > could reduce the noise-level overall from those build_skb() allocation failures > as it has a fall-back mechanism anyway. As Vlastimil already pointed out, __GFP_NOWARN would hide that reserves might be configured too low. -- Michal Hocko SUSE Labs