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([2620:10d:c090:500::2:84e7]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13b659c865asm13266118c88.11.2026.07.07.17.33.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 17:33:50 -0700 (PDT) Message-ID: <030dc01fa51430f4ac27d3f4eb4a6147322cb51d.camel@gmail.com> Subject: Re: [PATCH 0/3] selftests/bpf: compare BPF and memory.stat memcg stat readers From: Eduard Zingerman To: Shakeel Butt Cc: Ziyang Men , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Shuah Khan , Roman Gushchin , kernel-team@meta.com, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 07 Jul 2026 17:33:48 -0700 In-Reply-To: References: <20260704045617.487664-1-ziyang.meme@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) MIME-Version: 1.0 X-Stat-Signature: 4du19wr6of4ppsu97tst3y96xneg8qid X-Rspamd-Queue-Id: 31FC140002 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1783470832-132119 X-HE-Meta: U2FsdGVkX1+kQ0/kT0LJNZ1gYb5XbrLHysIh02x0RMjb6p2iKAVKS5NGStc3VBqHn3FBMmKNcDfFkZP+VMdt8M4WgIQJukz88lUIBDbdS23HD4oCa5Pd9OhZkTnCmRZVjI2XuLcW7lMxxMhX2J/x5qMpWcQjYGYIfse7HJ4Ge9hxTvASjB8JyhfsNourrHpRp/4wCFCi2N0PUt/sJTQhARTujsWKgiSaaNUMrpy4Z7f8V38RGpRuBhzgFwp6kOU2yc3NhMZVo/Qkcj/rfr1aiZoVHnWR/42FwtSJgw5JEZ8VIysF6T0t4XxeqsNUXjib5oLmnIXQn5DMLDR9Iwm0K2J/NXTQPkLvoESVcmZcMYpjRSixFVLrhYcICxmvyqufYZsSGyxqga9q5Q5nWTifkE2LSWbeYstID8KG7SRgTXMXv7wtwE6bO3P4buSq2eJlTaeVmJiLylKqIGrc+s885cBs7VyCbaGR0Kgf67XoIw3k8aDkEnkQXBcE7EeEDv4WnPSP4ejczcHJeJtbAKISeuHr/3qrdpqzGbj8HyFHCuG0n147TP8kHG6imaOmhoMIa8A8djycKQ2UhHmYXEWpqJsF83B6M2k5K+ZG0y84cbcGBqFv236DPpMqr6PWT5mUeUOUu51+aYyZu+/8SkmdalDrorM+/qrReKcd0FomjKVQyPBhxL+EVsy1KN1xGcyw6jEwv8sd7X1Y30bsLSXUwp/r6DgjSdeI0kQqEAM+D/kCffDSTby9zfLplPpmAMvVXuGTPiE+Vp/MVjcSSmhvwND6G/yqnYdrtSD7CqhsnUh7jrtEVgtcpcRKy4KbCQxKYg9J4dkC1o1vH0F4lz7XvVfqaNWnCKa8hCkKLPRq099pVu2cMjBMSt27+lapykhDtOYlfkgVa+tr7i1KCdXMVkDJ1V5EHPUg1lIC61abneb5ub6nt9+eCeRop8v0y6v2CK+qd8EjXmav7mJw4oT 4kC+XkB4 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2026-07-07 at 17:31 -0700, Shakeel Butt wrote: > On Tue, Jul 07, 2026 at 04:50:11PM -0700, Eduard Zingerman wrote: > > On Tue, 2026-07-07 at 16:27 -0700, Ziyang Men wrote: > > > But the patch also carries functional value: alongside that compariso= n, it > > > checks the correctness of the stats the kfuncs return. > > >=20 > > > Let me first answer the main question -- what these tests add over wh= at we > > > already have -- and then lay out a plan. > > >=20 > > > First, the static test (memcg_stat_reader) vs the existing cgroup_ite= r_memcg. > > >=20 > > > The existing test calls the kfuncs, but for each value it only checks= whether it > > > is greater than zero. For example, in prog_tests/cgroup_iter_memcg.c: > > >=20 > > > memset(map, 1, len); /* dirty some anon */ > > > if (!ASSERT_OK(read_stats(link), "read stats")) > > > goto cleanup; > > > ASSERT_GT(memcg_query->nr_anon_mapped, 0, "final anon mapped val= "); > > >=20 > > > It never checks the value is actually correct -- i.e. compares it aga= inst the > > > value in cgroupfs -- only that it is non-zero. > > >=20 > > > Besides, it also walks a single cgroup: > > >=20 > > > .cgroup.order =3D BPF_CGROUP_ITER_SELF_ONLY, > > >=20 > > > and reads only five fields. > >=20 > > Arguably one of the the cgroup_iter_memcg.c tests can be extended to > > allocate some mem and check if the value is reflected in the stats. > > But there is a line between MM tests and BPF tests. > > All BPF kfuncs except iterator logic itself are thin wrappers on > > top of the existing MM functionality. Hence, I don't think that > > BPF selftests are a place to stress-test these things. >=20 > That is actually a good discussion point. Where does such kind of tests (= i.e. > testing that bpf based memcg stats read functionality is equivalent to > traditional memcg stats reading). As more subsystems are exposed to bpf, = similar > questions would arise more often. >=20 > In this particular case, IIUC you want only tests for bpf related code (w= rappers > & iterator) to be present in bpf selftests, right? Yes, I think this makes most sense. > Personally I don't have strong opinion where this test should live. > Functionality wise as it is testing rstat infra, I think cgroup selftests= might > be better home for this.