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Wed, 31 Aug 2022 13:56:44 -0700 (PDT) MIME-Version: 1.0 References: <20220830214919.53220-1-surenb@google.com> <20220831084230.3ti3vitrzhzsu3fs@moria.home.lan> <20220831101948.f3etturccmp5ovkl@suse.de> <20220831190154.qdlsxfamans3ya5j@moria.home.lan> In-Reply-To: <20220831190154.qdlsxfamans3ya5j@moria.home.lan> From: Yosry Ahmed Date: Wed, 31 Aug 2022 13:56:08 -0700 Message-ID: Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications To: Kent Overstreet Cc: Michal Hocko , Mel Gorman , Peter Zijlstra , Suren Baghdasaryan , Andrew Morton , Vlastimil Babka , Johannes Weiner , Roman Gushchin , 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 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. (Sorry if you already posted this kind of data somewhere that I missed)