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Fri, 23 Jan 2026 12:47:05 -0800 (PST) Message-ID: Date: Fri, 23 Jan 2026 12:47:02 -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: [RFC PATCH bpf-next v3 09/12] selftests/bpf: Add tests for memcg_bpf_ops To: Hui Zhu , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , 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 , Peter Zijlstra , Miguel Ojeda , Nathan Chancellor , Kees Cook , Tejun Heo , Jeff Xu , mkoutny@suse.com, Jan Hendrik Farr , Christian Brauner , Randy Dunlap , Brian Gerst , Masahiro Yamada , davem@davemloft.net, Jakub Kicinski , Jesper Dangaard Brouer , Willem de Bruijn , Jason Xing , Paul Chaignon , Anton Protopopov , Amery Hung , Chen Ridong , Lance Yang , Jiayuan Chen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Hui Zhu , Geliang Tang References: Content-Language: en-US From: JP Kobryn In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Hui, On 1/23/26 1:00 AM, Hui Zhu wrote: > From: Hui Zhu > > Add a comprehensive selftest suite for the `memcg_bpf_ops` > functionality. These tests validate that BPF programs can correctly > influence memory cgroup throttling behavior by implementing the new > hooks. > > The test suite is added in `prog_tests/memcg_ops.c` and covers > several key scenarios: > > 1. `test_memcg_ops_over_high`: > Verifies that a BPF program can trigger throttling on a low-priority > cgroup by returning a delay from the `get_high_delay_ms` hook when a > high-priority cgroup is under pressure. > > 2. `test_memcg_ops_below_low_over_high`: > Tests the combination of the `below_low` and `get_high_delay_ms` > hooks, ensuring they work together as expected. > > 3. `test_memcg_ops_below_min_over_high`: > Validates the interaction between the `below_min` and > `get_high_delay_ms` hooks. > > The test framework sets up a cgroup hierarchy with high and low > priority groups, attaches BPF programs, runs memory-intensive > workloads, and asserts that the observed throttling (measured by > workload execution time) matches expectations. > > The BPF program (`progs/memcg_ops.c`) uses a tracepoint on > `memcg:count_memcg_events` (specifically PGFAULT) to detect memory > pressure and trigger the appropriate hooks in response. This test > suite provides essential validation for the new memory control > mechanisms. > > Signed-off-by: Geliang Tang > Signed-off-by: Hui Zhu > --- [..] > diff --git a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c > new file mode 100644 > index 000000000000..9a8d16296f2d > --- /dev/null > +++ b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c > @@ -0,0 +1,537 @@ [..] > + > +static void > +real_test_memcg_ops_child_work(const char *cgroup_path, > + char *data_filename, > + char *time_filename, > + int read_times) > +{ > + struct timeval start, end; > + double elapsed; > + FILE *fp; > + > + if (!ASSERT_OK(join_parent_cgroup(cgroup_path), "join_parent_cgroup")) > + goto out; > + > + if (env.verbosity >= VERBOSE_NORMAL) > + printf("%s %d begin\n", __func__, getpid()); > + > + gettimeofday(&start, NULL); > + > + if (!ASSERT_OK(write_file(data_filename), "write_file")) > + goto out; > + > + if (env.verbosity >= VERBOSE_NORMAL) > + printf("%s %d write_file done\n", __func__, getpid()); > + > + if (!ASSERT_OK(read_file(data_filename, read_times), "read_file")) > + goto out; > + > + gettimeofday(&end, NULL); > + > + elapsed = (end.tv_sec - start.tv_sec) + > + (end.tv_usec - start.tv_usec) / 1000000.0; > + > + if (env.verbosity >= VERBOSE_NORMAL) > + printf("%s %d end %.6f\n", __func__, getpid(), elapsed); > + > + fp = fopen(time_filename, "w"); > + if (!ASSERT_OK_PTR(fp, "fopen")) > + goto out; > + fprintf(fp, "%.6f", elapsed); > + fclose(fp); > + > +out: > + exit(0); > +} > + [..] > +static void real_test_memcg_ops(int read_times) > +{ > + int ret; > + char data_file1[] = "/tmp/test_data_XXXXXX"; > + char data_file2[] = "/tmp/test_data_XXXXXX"; > + char time_file1[] = "/tmp/test_time_XXXXXX"; > + char time_file2[] = "/tmp/test_time_XXXXXX"; > + pid_t pid1, pid2; > + double time1, time2; > + > + ret = mkstemp(data_file1); > + if (!ASSERT_GT(ret, 0, "mkstemp")) > + return; > + close(ret); > + ret = mkstemp(data_file2); > + if (!ASSERT_GT(ret, 0, "mkstemp")) > + goto cleanup_data_file1; > + close(ret); > + ret = mkstemp(time_file1); > + if (!ASSERT_GT(ret, 0, "mkstemp")) > + goto cleanup_data_file2; > + close(ret); > + ret = mkstemp(time_file2); > + if (!ASSERT_GT(ret, 0, "mkstemp")) > + goto cleanup_time_file1; > + close(ret); > + > + pid1 = fork(); > + if (!ASSERT_GE(pid1, 0, "fork")) > + goto cleanup; > + if (pid1 == 0) > + real_test_memcg_ops_child_work(CG_LOW_DIR, > + data_file1, > + time_file1, > + read_times); Would it be better to call exit() after real_test_memcg_ops_child_work() instead of within it? This way the fork/exit/wait logic is contained in the same scope making the lifetimes easier to track. I had to go back and search for the call to exit() since at a glance this function appears to proceed to call fork() and waitpid() from within both parent and child procs (though it really does not).