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From: Roman Gushchin To: Yosry Ahmed Cc: Kent Overstreet , Michal Hocko , Mel Gorman , Peter Zijlstra , Suren Baghdasaryan , Andrew Morton , Vlastimil Babka , Johannes Weiner , dave@stgolabs.net, Matthew Wilcox , liam.howlett@oracle.com, void@manifault.com, juri.lelli@redhat.com, ldufour@linux.ibm.com, Peter Xu , David Hildenbrand , axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, Steven Rostedt , bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, Christoph Lameter , Pekka Enberg , Joonsoo Kim , 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, Shakeel Butt , Muchun Song , arnd@arndb.de, jbaron@akamai.com, David Rientjes , minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, Linux-MM , iommu@lists.linux.dev, kasan-dev@googlegroups.com, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-modules@vger.kernel.org, Linux Kernel Mailing List Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications Message-ID: References: <20220830214919.53220-1-surenb@google.com> <20220831084230.3ti3vitrzhzsu3fs@moria.home.lan> <20220831101948.f3etturccmp5ovkl@suse.de> <20220831190154.qdlsxfamans3ya5j@moria.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662071274; a=rsa-sha256; cv=none; b=PqGw5tS6xyKJ3WIj/jPakdMkEeGxx0DtYcfoQ68QUQPaM3dmwgBxbi6Qhll5Ylpa+yqoCi jMZD9XdESpSmp+NHuf2SUhIJ/IANcuujO06S6J6UomZAGtmJXBgp1nvJKh0mIrZnXVSYUU 2D/WB+ZRtcyJI/QjxIZIEs7DzwPRvM4= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=bPfcK47f; spf=pass (imf23.hostedemail.com: domain of roman.gushchin@linux.dev designates 188.165.223.204 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662071274; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=b1dqv/ByZCeKtjIN7qAh4WTPe6OgIYJaSbL14h63ejE=; b=VUZx2vhixfxrDy5+XpwLwW4MHiZwhiPr+80/KjLGpJuA3Glog77ifmMV3BTehbWbfgHVNx cDO1sWKQKzg6Y4E9lLuYp5We5broC776DWa9BQax3YGtQPmq/jB8F53EcxrVmWPnz7JYM/ DD05MHN7zADT7VZ2+Ue9bxuQh0Ziqp0= X-Rspam-User: X-Stat-Signature: 3bzbcgx7uynfdydmw44z5i1cm4ocepe3 X-Rspamd-Queue-Id: 1669E140053 X-Rspamd-Server: rspam06 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=bPfcK47f; spf=pass (imf23.hostedemail.com: domain of roman.gushchin@linux.dev designates 188.165.223.204 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev X-HE-Tag: 1662071273-370535 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 31, 2022 at 01:56:08PM -0700, Yosry Ahmed wrote: > On Wed, Aug 31, 2022 at 12:02 PM Kent Overstreet > wrote: > > > > On Wed, Aug 31, 2022 at 12:47:32PM +0200, Michal Hocko wrote: > > > On Wed 31-08-22 11:19:48, Mel Gorman wrote: > > > > Whatever asking for an explanation as to why equivalent functionality > > > > cannot not be created from ftrace/kprobe/eBPF/whatever is reasonable. > > > > > > Fully agreed and this is especially true for a change this size > > > 77 files changed, 3406 insertions(+), 703 deletions(-) > > > > In the case of memory allocation accounting, you flat cannot do this with ftrace > > - you could maybe do a janky version that isn't fully accurate, much slower, > > more complicated for the developer to understand and debug and more complicated > > for the end user. > > > > But please, I invite anyone who's actually been doing this with ftrace to > > demonstrate otherwise. > > > > Ftrace just isn't the right tool for the job here - we're talking about adding > > per callsite accounting to some of the fastest fast paths in the kernel. > > > > And the size of the changes for memory allocation accounting are much more > > reasonable: > > 33 files changed, 623 insertions(+), 99 deletions(-) > > > > The code tagging library should exist anyways, it's been open coded half a dozen > > times in the kernel already. > > > > And once we've got that, the time stats code is _also_ far simpler than doing it > > with ftrace would be. If anyone here has successfully debugged latency issues > > with ftrace, I'd really like to hear it. Again, for debugging latency issues you > > want something that can always be on, and that's not cheap with ftrace - and > > never mind the hassle of correlating start and end wait trace events, builting > > up histograms, etc. - that's all handled here. > > > > Cheap, simple, easy to use. What more could you want? > > > > This is very interesting work! Do you have any data about the overhead > this introduces, especially in a production environment? I am > especially interested in memory allocations tracking and detecting > leaks. +1 I think the question whether it indeed can be always turned on in the production or not is the main one. If not, the advantage over ftrace/bpf/... is not that obvious. Otherwise it will be indeed a VERY useful thing. Also, there is a lot of interesting stuff within this patchset, which might be useful elsewhere. So thanks to Kent and Suren for this work! Thanks!