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Thu, 12 Feb 2026 16:38:56 -0800 (PST) Message-ID: <51bbd728-c712-4601-8a4a-7c602c67fe75@gmail.com> Date: Thu, 12 Feb 2026 16:38:54 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next 2/3] mm/memcontrol: Return error when accessing kmem with nokmem To: Hui Zhu , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Hui Zhu , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org References: <733422f72ccbac94126ae67b9e49f4a3d460b76a.1770883926.git.zhuhui@kylinos.cn> Content-Language: en-US From: "JP Kobryn (Meta)" In-Reply-To: <733422f72ccbac94126ae67b9e49f4a3d460b76a.1770883926.git.zhuhui@kylinos.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/12/26 12:23 AM, Hui Zhu wrote: > From: Hui Zhu > > When running tests on hosts with cgroup.memory=nokmem enabled for > performance reasons, test_kmem always gets a value of 0 for kmem > statistics. > > Since BPF programs cannot easily determine whether kmem is enabled, > add a check in memcg_stat_item_valid() to return an error when > attempting to access MEMCG_KMEM statistics while kmem accounting > is disabled via cgroup_memory_nokmem. > > This prevents BPF programs from silently receiving zero values and > allows them to properly handle the case where kmem accounting is > unavailable. > > Signed-off-by: Hui Zhu > --- > mm/memcontrol.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 129eed3ff5bb..4d8419623d1c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -667,7 +667,8 @@ unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx) > > bool memcg_stat_item_valid(int idx) > { > - if ((u32)idx >= MEMCG_NR_STAT) > + if ((u32)idx >= MEMCG_NR_STAT || > + (cgroup_memory_nokmem && (u32)idx == MEMCG_KMEM)) > return false; It's still a valid stat though, right? When it's disabled the value will just remain zero. I don't think this is necessary.