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Message-ID: <b90069a3-86b4-4fba-9ff3-fe5f6c4e425d@gmail.com>
Date: Fri, 23 Jan 2026 12:47:02 -0800
From: JP Kobryn <inwardvessel@...il.com>
To: Hui Zhu <hui.zhu@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>,
Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
<martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Miguel Ojeda <ojeda@...nel.org>,
Nathan Chancellor <nathan@...nel.org>, Kees Cook <kees@...nel.org>,
Tejun Heo <tj@...nel.org>, Jeff Xu <jeffxu@...omium.org>, mkoutny@...e.com,
Jan Hendrik Farr <kernel@...rr.cc>, Christian Brauner <brauner@...nel.org>,
Randy Dunlap <rdunlap@...radead.org>, Brian Gerst <brgerst@...il.com>,
Masahiro Yamada <masahiroy@...nel.org>, davem@...emloft.net,
Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
Willem de Bruijn <willemb@...gle.com>, Jason Xing
<kerneljasonxing@...il.com>, Paul Chaignon <paul.chaignon@...il.com>,
Anton Protopopov <a.s.protopopov@...il.com>, Amery Hung
<ameryhung@...il.com>, Chen Ridong <chenridong@...weicloud.com>,
Lance Yang <lance.yang@...ux.dev>, Jiayuan Chen <jiayuan.chen@...ux.dev>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, cgroups@...r.kernel.org,
bpf@...r.kernel.org, netdev@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: Hui Zhu <zhuhui@...inos.cn>, Geliang Tang <geliang@...nel.org>
Subject: Re: [RFC PATCH bpf-next v3 09/12] selftests/bpf: Add tests for
memcg_bpf_ops
Hi Hui,
On 1/23/26 1:00 AM, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@...inos.cn>
>
> 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 <geliang@...nel.org>
> Signed-off-by: Hui Zhu <zhuhui@...inos.cn>
> ---
[..]
> 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).
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