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 671FEC3A5A7 for ; Wed, 4 Sep 2019 15:38:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D5C222CEA for ; Wed, 4 Sep 2019 15:38:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567611483; bh=AKawEZgQyjTKSRtTHeHh9Xyr+24+V3DlM/zrWOKaALU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=GMSWisYIxrRuMAxJzFndE6vDds86ZwKJbk9argzld6hIb4Zj0TTG4dferf3AxCOPo hs1O2g7sf9l73lh1M5pluIMQ+GZ0b1W2pnb06r01tBpkc2C8A4SA5XAOIMFvaOcWmH oHTjUtsQ7NN7kmRkJ5PhUwV8UjDQMnz3olzaoiYg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731360AbfIDPiC (ORCPT ); Wed, 4 Sep 2019 11:38:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:45060 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725965AbfIDPiB (ORCPT ); Wed, 4 Sep 2019 11:38:01 -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 50AEAB01E; Wed, 4 Sep 2019 15:38:00 +0000 (UTC) Date: Wed, 4 Sep 2019 17:37:59 +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: <20190904153759.GC3838@dhcp22.suse.cz> References: <20190903200905.198642-1-joel@joelfernandes.org> <20190904084508.GL3838@dhcp22.suse.cz> <20190904153258.GH240514@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904153258.GH240514@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 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? > but also for reducing > tracing noise. Flooding the traces makes it less useful for long traces and > post-processing of traces. IOW, the overhead reduction is a bonus. This is not really anything special for this tracepoint though. Basically any tracepoint in a hot path is in the same situation and I do not see a point why each of them should really invent its own way to throttle. Maybe there is some way to do that in the tracing subsystem directly. -- Michal Hocko SUSE Labs