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Message-ID: <874iu1mt5h.fsf@linux.dev>
Date: Wed, 20 Aug 2025 17:10:18 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: linux-mm@...ck.org, bpf@...r.kernel.org, Suren Baghdasaryan
<surenb@...gle.com>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko
<mhocko@...e.com>, David Rientjes <rientjes@...gle.com>, Matt Bobrowski
<mattbobrowski@...gle.com>, Song Liu <song@...nel.org>, Kumar Kartikeya
Dwivedi <memxor@...il.com>, Alexei Starovoitov <ast@...nel.org>, Andrew
Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 10/14] bpf: selftests: bpf OOM handler test
Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
> On Mon, Aug 18, 2025 at 10:05 AM Roman Gushchin
> <roman.gushchin@...ux.dev> wrote:
>>
>> Implement a pseudo-realistic test for the OOM handling
>> functionality.
>>
>> The OOM handling policy which is implemented in bpf is to
>> kill all tasks belonging to the biggest leaf cgroup, which
>> doesn't contain unkillable tasks (tasks with oom_score_adj
>> set to -1000). Pagecache size is excluded from the accounting.
>>
>> The test creates a hierarchy of memory cgroups, causes an
>> OOM at the top level, checks that the expected process will be
>> killed and checks memcg's oom statistics.
>>
>> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
>> ---
>> .../selftests/bpf/prog_tests/test_oom.c | 229 ++++++++++++++++++
>> tools/testing/selftests/bpf/progs/test_oom.c | 108 +++++++++
>> 2 files changed, 337 insertions(+)
>> create mode 100644 tools/testing/selftests/bpf/prog_tests/test_oom.c
>> create mode 100644 tools/testing/selftests/bpf/progs/test_oom.c
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/test_oom.c b/tools/testing/selftests/bpf/prog_tests/test_oom.c
>> new file mode 100644
>> index 000000000000..eaeb14a9d18f
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/test_oom.c
>> @@ -0,0 +1,229 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +#include <test_progs.h>
>> +#include <bpf/btf.h>
>> +#include <bpf/bpf.h>
>> +
>> +#include "cgroup_helpers.h"
>> +#include "test_oom.skel.h"
>> +
>> +struct cgroup_desc {
>> + const char *path;
>> + int fd;
>> + unsigned long long id;
>> + int pid;
>> + size_t target;
>> + size_t max;
>> + int oom_score_adj;
>> + bool victim;
>> +};
>> +
>> +#define MB (1024 * 1024)
>> +#define OOM_SCORE_ADJ_MIN (-1000)
>> +#define OOM_SCORE_ADJ_MAX 1000
>> +
>> +static struct cgroup_desc cgroups[] = {
>> + { .path = "/oom_test", .max = 80 * MB},
>> + { .path = "/oom_test/cg1", .target = 10 * MB,
>> + .oom_score_adj = OOM_SCORE_ADJ_MAX },
>> + { .path = "/oom_test/cg2", .target = 40 * MB,
>> + .oom_score_adj = OOM_SCORE_ADJ_MIN },
>> + { .path = "/oom_test/cg3" },
>> + { .path = "/oom_test/cg3/cg4", .target = 30 * MB,
>> + .victim = true },
>> + { .path = "/oom_test/cg3/cg5", .target = 20 * MB },
>> +};
>> +
>> +static int spawn_task(struct cgroup_desc *desc)
>> +{
>> + char *ptr;
>> + int pid;
>> +
>> + pid = fork();
>> + if (pid < 0)
>> + return pid;
>> +
>> + if (pid > 0) {
>> + /* parent */
>> + desc->pid = pid;
>> + return 0;
>> + }
>> +
>> + /* child */
>> + if (desc->oom_score_adj) {
>> + char buf[64];
>> + int fd = open("/proc/self/oom_score_adj", O_WRONLY);
>> +
>> + if (fd < 0)
>> + return -1;
>> +
>> + snprintf(buf, sizeof(buf), "%d", desc->oom_score_adj);
>> + write(fd, buf, sizeof(buf));
>> + close(fd);
>> + }
>> +
>> + ptr = (char *)malloc(desc->target);
>> + if (!ptr)
>> + return -ENOMEM;
>> +
>> + memset(ptr, 'a', desc->target);
>> +
>> + while (1)
>> + sleep(1000);
>> +
>> + return 0;
>> +}
>> +
>> +static void setup_environment(void)
>> +{
>> + int i, err;
>> +
>> + err = setup_cgroup_environment();
>> + if (!ASSERT_OK(err, "setup_cgroup_environment"))
>> + goto cleanup;
>> +
>> + for (i = 0; i < ARRAY_SIZE(cgroups); i++) {
>> + cgroups[i].fd = create_and_get_cgroup(cgroups[i].path);
>> + if (!ASSERT_GE(cgroups[i].fd, 0, "create_and_get_cgroup"))
>> + goto cleanup;
>> +
>> + cgroups[i].id = get_cgroup_id(cgroups[i].path);
>> + if (!ASSERT_GT(cgroups[i].id, 0, "get_cgroup_id"))
>> + goto cleanup;
>> +
>> + /* Freeze the top-level cgroup */
>> + if (i == 0) {
>> + /* Freeze the top-level cgroup */
>> + err = write_cgroup_file(cgroups[i].path, "cgroup.freeze", "1");
>> + if (!ASSERT_OK(err, "freeze cgroup"))
>> + goto cleanup;
>> + }
>> +
>> + /* Recursively enable the memory controller */
>> + if (!cgroups[i].target) {
>> +
>> + err = write_cgroup_file(cgroups[i].path, "cgroup.subtree_control",
>> + "+memory");
>> + if (!ASSERT_OK(err, "enable memory controller"))
>> + goto cleanup;
>> + }
>> +
>> + /* Set memory.max */
>> + if (cgroups[i].max) {
>> + char buf[256];
>> +
>> + snprintf(buf, sizeof(buf), "%lu", cgroups[i].max);
>> + err = write_cgroup_file(cgroups[i].path, "memory.max", buf);
>> + if (!ASSERT_OK(err, "set memory.max"))
>> + goto cleanup;
>> +
>> + snprintf(buf, sizeof(buf), "0");
>> + write_cgroup_file(cgroups[i].path, "memory.swap.max", buf);
>> +
>> + }
>> +
>> + /* Spawn tasks creating memory pressure */
>> + if (cgroups[i].target) {
>> + char buf[256];
>> +
>> + err = spawn_task(&cgroups[i]);
>> + if (!ASSERT_OK(err, "spawn task"))
>> + goto cleanup;
>> +
>> + snprintf(buf, sizeof(buf), "%d", cgroups[i].pid);
>> + err = write_cgroup_file(cgroups[i].path, "cgroup.procs", buf);
>> + if (!ASSERT_OK(err, "put child into a cgroup"))
>> + goto cleanup;
>> + }
>> + }
>> +
>> + return;
>> +
>> +cleanup:
>> + cleanup_cgroup_environment();
>> +}
>> +
>> +static int run_and_wait_for_oom(void)
>> +{
>> + int ret = -1;
>> + bool first = true;
>> + char buf[4096] = {};
>> + size_t size;
>> +
>> + /* Unfreeze the top-level cgroup */
>> + ret = write_cgroup_file(cgroups[0].path, "cgroup.freeze", "0");
>> + if (!ASSERT_OK(ret, "freeze cgroup"))
>> + return -1;
>> +
>> + for (;;) {
>> + int i, status;
>> + pid_t pid = wait(&status);
>> +
>> + if (pid == -1) {
>> + if (errno == EINTR)
>> + continue;
>> + /* ECHILD */
>> + break;
>> + }
>> +
>> + if (!first)
>> + continue;
>> +
>> + first = false;
>> +
>> + /* Check which process was terminated first */
>> + for (i = 0; i < ARRAY_SIZE(cgroups); i++) {
>> + if (!ASSERT_OK(cgroups[i].victim !=
>> + (pid == cgroups[i].pid),
>> + "correct process was killed")) {
>> + ret = -1;
>> + break;
>> + }
>> +
>> + if (!cgroups[i].victim)
>> + continue;
>> +
>> + /* Check the memcg oom counter */
>> + size = read_cgroup_file(cgroups[i].path,
>> + "memory.events",
>> + buf, sizeof(buf));
>> + if (!ASSERT_OK(size <= 0, "read memory.events")) {
>> + ret = -1;
>> + break;
>> + }
>> +
>> + if (!ASSERT_OK(strstr(buf, "oom_kill 1") == NULL,
>> + "oom_kill count check")) {
>> + ret = -1;
>> + break;
>> + }
>> + }
>> +
>> + /* Kill all remaining tasks */
>> + for (i = 0; i < ARRAY_SIZE(cgroups); i++)
>> + if (cgroups[i].pid && cgroups[i].pid != pid)
>> + kill(cgroups[i].pid, SIGKILL);
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +void test_oom(void)
>> +{
>> + struct test_oom *skel;
>> + int err;
>> +
>> + setup_environment();
>> +
>> + skel = test_oom__open_and_load();
>> + err = test_oom__attach(skel);
>> + if (CHECK_FAIL(err))
>> + goto cleanup;
>> +
>> + /* Unfreeze all child tasks and create the memory pressure */
>> + err = run_and_wait_for_oom();
>> + CHECK_FAIL(err);
>> +
>> +cleanup:
>> + cleanup_cgroup_environment();
>> + test_oom__destroy(skel);
>> +}
>> diff --git a/tools/testing/selftests/bpf/progs/test_oom.c b/tools/testing/selftests/bpf/progs/test_oom.c
>> new file mode 100644
>> index 000000000000..ca83563fc9a8
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/test_oom.c
>> @@ -0,0 +1,108 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +#include "vmlinux.h"
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +#define OOM_SCORE_ADJ_MIN (-1000)
>> +
>> +void bpf_rcu_read_lock(void) __ksym;
>> +void bpf_rcu_read_unlock(void) __ksym;
>> +struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
>> +void bpf_task_release(struct task_struct *p) __ksym;
>> +struct mem_cgroup *bpf_get_root_mem_cgroup(void) __ksym;
>> +struct mem_cgroup *bpf_get_mem_cgroup(struct cgroup_subsys_state *css) __ksym;
>> +void bpf_put_mem_cgroup(struct mem_cgroup *memcg) __ksym;
>> +int bpf_oom_kill_process(struct oom_control *oc, struct task_struct *task,
>> + const char *message__str) __ksym;
>
> These declarations should come from vmlinux.h, if you don't get them,
> you might not have recent enough pahole.
Indeed. Fixed, thanks!
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