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From: Roman Gushchin To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, ldufour@linux.ibm.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, tj@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, andreyknvl@gmail.com, keescook@chromium.org, ndesaulniers@google.com, gregkh@linuxfoundation.org, ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org Subject: Re: [PATCH 00/40] Memory allocation profiling Message-ID: References: <20230501165450.15352-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, May 01, 2023 at 11:08:05AM -0700, Suren Baghdasaryan wrote: > On Mon, May 1, 2023 at 10:47 AM Roman Gushchin wrote: > > > > On Mon, May 01, 2023 at 09:54:10AM -0700, Suren Baghdasaryan wrote: > > > Performance overhead: > > > To evaluate performance we implemented an in-kernel test executing > > > multiple get_free_page/free_page and kmalloc/kfree calls with allocation > > > sizes growing from 8 to 240 bytes with CPU frequency set to max and CPU > > > affinity set to a specific CPU to minimize the noise. Below is performance > > > comparison between the baseline kernel, profiling when enabled, profiling > > > when disabled (nomem_profiling=y) and (for comparison purposes) baseline > > > with CONFIG_MEMCG_KMEM enabled and allocations using __GFP_ACCOUNT: > > > > > > kmalloc pgalloc > > > Baseline (6.3-rc7) 9.200s 31.050s > > > profiling disabled 9.800 (+6.52%) 32.600 (+4.99%) > > > profiling enabled 12.500 (+35.87%) 39.010 (+25.60%) > > > memcg_kmem enabled 41.400 (+350.00%) 70.600 (+127.38%) > > > > Hm, this makes me think we have a regression with memcg_kmem in one of > > the recent releases. When I measured it a couple of years ago, the overhead > > was definitely within 100%. > > > > Do you understand what makes the your profiling drastically faster than kmem? > > I haven't profiled or looked into kmem overhead closely but I can do > that. I just wanted to see how the overhead compares with the existing > accounting mechanisms. It's a good idea and I generally think that +25-35% for kmalloc/pgalloc should be ok for the production use, which is great! In the reality, most workloads are not that sensitive to the speed of memory allocation. > > For kmalloc, the overhead is low because after we create the vector of > slab_ext objects (which is the same as what memcg_kmem does), memory > profiling just increments a lazy counter (which in many cases would be > a per-cpu counter). So does kmem (this is why I'm somewhat surprised by the difference). > memcg_kmem operates on cgroup hierarchy with > additional overhead associated with that. I'm guessing that's the > reason for the big difference between these mechanisms but, I didn't > look into the details to understand memcg_kmem performance. I suspect recent rt-related changes and also the wide usage of rcu primitives in the kmem code. I'll try to look closer as well. Thanks!