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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C058CECAAD3 for ; Thu, 1 Sep 2022 22:37:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235060AbiIAWhc (ORCPT ); Thu, 1 Sep 2022 18:37:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233598AbiIAWha (ORCPT ); Thu, 1 Sep 2022 18:37:30 -0400 Received: from out1.migadu.com (out1.migadu.com [IPv6:2001:41d0:2:863f::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D205C642C4; Thu, 1 Sep 2022 15:37:29 -0700 (PDT) Date: Thu, 1 Sep 2022 18:37:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1662071848; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=V/P7j4Y+xJUBAt6fEYfNoKfACstBZQ8E1OFd7bHElGY=; b=RyUvH2zz81kL6tcYdp2BW6QKmetndFvVS3i7VcCPOcaijLcz0TfOGgBaq909SL/Y1jdlP0 /Retvz17eFHQUiP5AcXQOlPHDOkvuT6UrIyhDdDGO5y36J1883WvsJluGTqXU9etuyqcdH dSwrFVK7mCUuYhH+U9EIxQUe3RmbsW8= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kent Overstreet To: Roman Gushchin Cc: Yosry Ahmed , 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: <20220901223720.e4gudprscjtwltif@moria.home.lan> 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 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Sep 01, 2022 at 03:27:27PM -0700, Roman Gushchin wrote: > On Wed, Aug 31, 2022 at 01:56:08PM -0700, Yosry Ahmed wrote: > > 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. Low enough overhead to run in production was my primary design goal. Stats are kept in a struct that's defined at the callsite. So this adds _no_ pointer chasing to the allocation path, unless we've switch to percpu counters at that callsite (see the lazy percpu counters patch), where we need to deref one percpu pointer to save an atomic. Then we need to stash a pointer to the alloc_tag, so that kfree() can find it. For slab allocations this uses the same storage area as memcg, so for allocations that are using that we won't be touching any additional cachelines. (I wanted the pointer to the alloc_tag to be stored inline with the allocation, but that would've caused alignment difficulties). Then there's a pointer deref introduced to the kfree() path, to get back to the original alloc_tag and subtract the allocation from that callsite. That one won't be free, and with percpu counters we've got another dependent load too - hmm, it might be worth benchmarking with just atomics, skipping the percpu counters. So the overhead won't be zero, I expect it'll show up in some synthetic benchmarks, but yes I do definitely expect this to be worth enabling in production in many scenarios.