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 95B28C0030B for ; Thu, 5 Sep 2019 14:20:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1C34206CD for ; Thu, 5 Sep 2019 14:20:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567693214; bh=Q/wop4+TbQrDGzkdGySYx4C8Obj8YD0BcMoje+4adYc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ZNi7XDZoteZqncvolUMoQjkvdMrJohNiCpe64vRNVfgw8DKAZ7u4ZiUFMYOWlkfly GvMi+57M28eCcJPJNr7awUEhOnTjHPbaQ1ESejmqFdzmOwWxQyMY00LG9xeWxT0CXc 1KdCa850clv4e9mARQLqnrR/LalnZtHD8Hah074k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388288AbfIEOUN (ORCPT ); Thu, 5 Sep 2019 10:20:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:47510 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725290AbfIEOUN (ORCPT ); Thu, 5 Sep 2019 10:20:13 -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 A5554AF92; Thu, 5 Sep 2019 14:20:11 +0000 (UTC) Date: Thu, 5 Sep 2019 16:20:10 +0200 From: Michal Hocko To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Tim Murray , carmenjackson@google.com, mayankgupta@google.com, dancol@google.com, rostedt@goodmis.org, minchan@kernel.org, akpm@linux-foundation.org, kernel-team@android.com, "Aneesh Kumar K.V" , Dan Williams , Jerome Glisse , linux-mm@kvack.org, Matthew Wilcox , Ralph Campbell , Vlastimil Babka Subject: Re: [PATCH v2] mm: emit tracepoint when RSS changes by threshold Message-ID: <20190905142010.GC3838@dhcp22.suse.cz> References: <20190903200905.198642-1-joel@joelfernandes.org> <20190904084508.GL3838@dhcp22.suse.cz> <20190904153258.GH240514@google.com> <20190904153759.GC3838@dhcp22.suse.cz> <20190904162808.GO240514@google.com> <20190905105424.GG3838@dhcp22.suse.cz> <20190905141452.GA26466@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190905141452.GA26466@google.com> 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 Thu 05-09-19 10:14:52, Joel Fernandes wrote: > On Thu, Sep 05, 2019 at 12:54:24PM +0200, Michal Hocko wrote: > > On Wed 04-09-19 12:28:08, Joel Fernandes wrote: > > > On Wed, Sep 4, 2019 at 11:38 AM Michal Hocko wrote: > > > > > > > > On Wed 04-09-19 11:32:58, Joel Fernandes wrote: > > > > > On Wed, Sep 04, 2019 at 10:45:08AM +0200, Michal Hocko wrote: > > > > > > On Tue 03-09-19 16:09:05, Joel Fernandes (Google) wrote: > > > > > > > Useful to track how RSS is changing per TGID to detect spikes in RSS and > > > > > > > memory hogs. Several Android teams have been using this patch in various > > > > > > > kernel trees for half a year now. Many reported to me it is really > > > > > > > useful so I'm posting it upstream. > > > > > > > > > > > > > > Initial patch developed by Tim Murray. Changes I made from original patch: > > > > > > > o Prevent any additional space consumed by mm_struct. > > > > > > > o Keep overhead low by checking if tracing is enabled. > > > > > > > o Add some noise reduction and lower overhead by emitting only on > > > > > > > threshold changes. > > > > > > > > > > > > Does this have any pre-requisite? I do not see trace_rss_stat_enabled in > > > > > > the Linus tree (nor in linux-next). > > > > > > > > > > No, this is generated automatically by the tracepoint infrastructure when a > > > > > tracepoint is added. > > > > > > > > OK, I was not aware of that. > > > > > > > > > > Besides that why do we need batching in the first place. Does this have a > > > > > > measurable overhead? How does it differ from any other tracepoints that we > > > > > > have in other hotpaths (e.g. page allocator doesn't do any checks). > > > > > > > > > > We do need batching not only for overhead reduction, > > > > > > > > What is the overhead? > > > > > > The overhead is occasionally higher without the threshold (that is if we > > > trace every counter change). I would classify performance benefit to be > > > almost the same and within the noise. > > > > OK, so the additional code is not really justified. > > It is really justified. Did you read the whole of the last email? Of course I have. The information that numbers are in noise with some outliers (without any details about the underlying reason) is simply showing that you are optimizing something probably not worth it. I would recommend adding a simple tracepoint. That should be pretty non controversial. And if you want to add an optimization on top then provide data to justify it. -- Michal Hocko SUSE Labs