Message-ID: <aecf051c-6f56-b799-bbc9-148892b584b6@bytedance.com>
Date:   Wed, 16 Aug 2023 22:34:26 +0800
From:   Chuyi Zhou <zhouchuyi@...edance.com>
To:     Alan Maguire <alan.maguire@...cle.com>, hannes@...xchg.org,
        mhocko@...nel.org, roman.gushchin@...ux.dev, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, muchun.song@...ux.dev
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        wuyun.abel@...edance.com, robin.lu@...edance.com
Subject: Re: [RFC PATCH v2 4/5] bpf: Add a OOM policy test

Hello,

在 2023/8/16 21:49, Alan Maguire 写道:
> On 16/08/2023 13:31, Chuyi Zhou wrote:
>> Hello,
>>
>> 在 2023/8/16 19:53, Alan Maguire 写道:
>>> On 10/08/2023 09:13, Chuyi Zhou wrote:
>>>> This patch adds a test which implements a priority-based policy through
>>>> bpf_oom_evaluate_task.
>>>>
>>>> The BPF program, oom_policy.c, compares the cgroup priority of two tasks
>>>> and select the lower one. The userspace program test_oom_policy.c
>>>> maintains a priority map by using cgroup id as the keys and priority as
>>>> the values. We could protect certain cgroups from oom-killer by setting
>>>> higher priority.
>>>>
>>>> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
>>>> ---
>>>>    .../bpf/prog_tests/test_oom_policy.c          | 140 ++++++++++++++++++
>>>>    .../testing/selftests/bpf/progs/oom_policy.c  | 104 +++++++++++++
>>>>    2 files changed, 244 insertions(+)
>>>>    create mode 100644
>>>> tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
>>>>    create mode 100644 tools/testing/selftests/bpf/progs/oom_policy.c
>>>>
>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
>>>> b/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
>>>> new file mode 100644
>>>> index 000000000000..bea61ff22603
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
>>>> @@ -0,0 +1,140 @@
>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>> +#define _GNU_SOURCE
>>>> +
>>>> +#include <stdio.h>
>>>> +#include <fcntl.h>
>>>> +#include <unistd.h>
>>>> +#include <stdlib.h>
>>>> +#include <signal.h>
>>>> +#include <sys/stat.h>
>>>> +#include <test_progs.h>
>>>> +#include <bpf/btf.h>
>>>> +#include <bpf/bpf.h>
>>>> +
>>>> +#include "cgroup_helpers.h"
>>>> +#include "oom_policy.skel.h"
>>>> +
>>>> +static int map_fd;
>>>> +static int cg_nr;
>>>> +struct {
>>>> +    const char *path;
>>>> +    int fd;
>>>> +    unsigned long long id;
>>>> +} cgs[] = {
>>>> +    { "/cg1" },
>>>> +    { "/cg2" },
>>>> +};
>>>> +
>>>> +
>>>> +static struct oom_policy *open_load_oom_policy_skel(void)
>>>> +{
>>>> +    struct oom_policy *skel;
>>>> +    int err;
>>>> +
>>>> +    skel = oom_policy__open();
>>>> +    if (!ASSERT_OK_PTR(skel, "skel_open"))
>>>> +        return NULL;
>>>> +
>>>> +    err = oom_policy__load(skel);
>>>> +    if (!ASSERT_OK(err, "skel_load"))
>>>> +        goto cleanup;
>>>> +
>>>> +    return skel;
>>>> +
>>>> +cleanup:
>>>> +    oom_policy__destroy(skel);
>>>> +    return NULL;
>>>> +}
>>>> +
>>>> +static void run_memory_consume(unsigned long long consume_size, int
>>>> idx)
>>>> +{
>>>> +    char *buf;
>>>> +
>>>> +    join_parent_cgroup(cgs[idx].path);
>>>> +    buf = malloc(consume_size);
>>>> +    memset(buf, 0, consume_size);
>>>> +    sleep(2);
>>>> +    exit(0);
>>>> +}
>>>> +
>>>> +static int set_cgroup_prio(unsigned long long cg_id, int prio)
>>>> +{
>>>> +    int err;
>>>> +
>>>> +    err = bpf_map_update_elem(map_fd, &cg_id, &prio, BPF_ANY);
>>>> +    ASSERT_EQ(err, 0, "update_map");
>>>> +    return err;
>>>> +}
>>>> +
>>>> +static int prepare_cgroup_environment(void)
>>>> +{
>>>> +    int err;
>>>> +
>>>> +    err = setup_cgroup_environment();
>>>> +    if (err)
>>>> +        goto clean_cg_env;
>>>> +    for (int i = 0; i < cg_nr; i++) {
>>>> +        err = cgs[i].fd = create_and_get_cgroup(cgs[i].path);
>>>> +        if (!ASSERT_GE(cgs[i].fd, 0, "cg_create"))
>>>> +            goto clean_cg_env;
>>>> +        cgs[i].id = get_cgroup_id(cgs[i].path);
>>>> +    }
>>>> +    return 0;
>>>> +clean_cg_env:
>>>> +    cleanup_cgroup_environment();
>>>> +    return err;
>>>> +}
>>>> +
>>>> +void test_oom_policy(void)
>>>> +{
>>>> +    struct oom_policy *skel;
>>>> +    struct bpf_link *link;
>>>> +    int err;
>>>> +    int victim_pid;
>>>> +    unsigned long long victim_cg_id;
>>>> +
>>>> +    link = NULL;
>>>> +    cg_nr = ARRAY_SIZE(cgs);
>>>> +
>>>> +    skel = open_load_oom_policy_skel();
>>>> +    err = oom_policy__attach(skel);
>>>> +    if (!ASSERT_OK(err, "oom_policy__attach"))
>>>> +        goto cleanup;
>>>> +
>>>> +    map_fd = bpf_object__find_map_fd_by_name(skel->obj, "cg_map");
>>>> +    if (!ASSERT_GE(map_fd, 0, "find map"))
>>>> +        goto cleanup;
>>>> +
>>>> +    err = prepare_cgroup_environment();
>>>> +    if (!ASSERT_EQ(err, 0, "prepare cgroup env"))
>>>> +        goto cleanup;
>>>> +
>>>> +    write_cgroup_file("/", "memory.max", "10M");
>>>> +
>>>> +    /*
>>>> +     * Set higher priority to cg2 and lower to cg1, so we would select
>>>> +     * task under cg1 as victim.(see oom_policy.c)
>>>> +     */
>>>> +    set_cgroup_prio(cgs[0].id, 10);
>>>> +    set_cgroup_prio(cgs[1].id, 50);
>>>> +
>>>> +    victim_cg_id = cgs[0].id;
>>>> +    victim_pid = fork();
>>>> +
>>>> +    if (victim_pid == 0)
>>>> +        run_memory_consume(1024 * 1024 * 4, 0);
>>>> +
>>>> +    if (fork() == 0)
>>>> +        run_memory_consume(1024 * 1024 * 8, 1);
>>>> +
>>>> +    while (wait(NULL) > 0)
>>>> +        ;
>>>> +
>>>> +    ASSERT_EQ(skel->bss->victim_pid, victim_pid, "victim_pid");
>>>> +    ASSERT_EQ(skel->bss->victim_cg_id, victim_cg_id, "victim_cgid");
>>>> +    ASSERT_EQ(skel->bss->failed_cnt, 1, "failed_cnt");
>>>> +cleanup:
>>>> +    bpf_link__destroy(link);
>>>> +    oom_policy__destroy(skel);
>>>> +    cleanup_cgroup_environment();
>>>> +}
>>>> diff --git a/tools/testing/selftests/bpf/progs/oom_policy.c
>>>> b/tools/testing/selftests/bpf/progs/oom_policy.c
>>>> new file mode 100644
>>>> index 000000000000..fc9efc93914e
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/bpf/progs/oom_policy.c
>>>> @@ -0,0 +1,104 @@
>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>> +#include <vmlinux.h>
>>>> +#include <bpf/bpf_tracing.h>
>>>> +#include <bpf/bpf_helpers.h>
>>>> +
>>>> +char _license[] SEC("license") = "GPL";
>>>> +
>>>> +struct {
>>>> +    __uint(type, BPF_MAP_TYPE_HASH);
>>>> +    __type(key, int);
>>>> +    __type(value, int);
>>>> +    __uint(max_entries, 24);
>>>> +} cg_map SEC(".maps");
>>>> +
>>>> +unsigned int victim_pid;
>>>> +u64 victim_cg_id;
>>>> +int failed_cnt;
>>>> +
>>>> +#define    EOPNOTSUPP    95
>>>> +
>>>> +enum {
>>>> +    NO_BPF_POLICY,
>>>> +    BPF_EVAL_ABORT,
>>>> +    BPF_EVAL_NEXT,
>>>> +    BPF_EVAL_SELECT,
>>>> +};
>>>
>>> When I built a kernel using this series and tried building the
>>> associated test for that kernel I saw:
>>>
>>> progs/oom_policy.c:22:2: error: redefinition of enumerator
>>> 'NO_BPF_POLICY'
>>>           NO_BPF_POLICY,
>>>           ^
>>> /home/opc/src/bpf-next/tools/testing/selftests/bpf/tools/include/vmlinux.h:75894:2:
>>> note: previous definition is here
>>>           NO_BPF_POLICY = 0,
>>>           ^
>>> progs/oom_policy.c:23:2: error: redefinition of enumerator
>>> 'BPF_EVAL_ABORT'
>>>           BPF_EVAL_ABORT,
>>>           ^
>>> /home/opc/src/bpf-next/tools/testing/selftests/bpf/tools/include/vmlinux.h:75895:2:
>>> note: previous definition is here
>>>           BPF_EVAL_ABORT = 1,
>>>           ^
>>> progs/oom_policy.c:24:2: error: redefinition of enumerator
>>> 'BPF_EVAL_NEXT'
>>>           BPF_EVAL_NEXT,
>>>           ^
>>> /home/opc/src/bpf-next/tools/testing/selftests/bpf/tools/include/vmlinux.h:75896:2:
>>> note: previous definition is here
>>>           BPF_EVAL_NEXT = 2,
>>>           ^
>>> progs/oom_policy.c:  CLNG-BPF [test_maps] tailcall_bpf2bpf4.bpf.o
>>> 25:2: error: redefinition of enumerator 'BPF_EVAL_SELECT'
>>>           BPF_EVAL_SELECT,
>>>           ^
>>> /home/opc/src/bpf-next/tools/testing/selftests/bpf/tools/include/vmlinux.h:75897:2:
>>> note: previous definition is here
>>>           BPF_EVAL_SELECT = 3,
>>>           ^
>>> 4 errors generated.
>>>
>>>
>>> So you shouldn't need the enum definition since it already makes it into
>>> vmlinux.h.
>>> OK. It seems my vmlinux.h doesn't contain these enum...
>>> I also ran into test failures when I removed the above (and compilation
>>> succeeded):
>>>
>>>
>>> test_oom_policy:PASS:prepare cgroup env 0 nsec
>>> (cgroup_helpers.c:130: errno: No such file or directory) Opening
>>> /mnt/cgroup-test-work-dir23054//memory.max
>>> set_cgroup_prio:PASS:update_map 0 nsec
>>> set_cgroup_prio:PASS:update_map 0 nsec
>>> test_oom_policy:FAIL:victim_pid unexpected victim_pid: actual 0 !=
>>> expected 23058
>>> test_oom_policy:FAIL:victim_cgid unexpected victim_cgid: actual 0 !=
>>> expected 68
>>> test_oom_policy:FAIL:failed_cnt unexpected failed_cnt: actual 0 !=
>>> expected 1
>>> #154     oom_policy:FAIL
>>> Summary: 1/0 PASSED, 0 SKIPPED, 1 FAILED
>>>
>>> So it seems that because my system was using the cgroupv1 memory
>>> controller, it could not be used for v2 unless I rebooted with
>>>
>>> systemd.unified_cgroup_hierarchy=1
>>>
>>> ...on the boot commandline. It would be good to note any such
>>> requirements for this test in the selftests/bpf/README.rst.
>>> Might also be worth adding
>>>
>>> write_cgroup_file("", "cgroup.subtree_control", "+memory");
>>>
>>> ...to ensure the memory controller is enabled for the root cgroup.
>>>
>>> At that point the test still failed:
>>>
>>> set_cgroup_prio:PASS:update_map 0 nsec
>>> test_oom_policy:FAIL:victim_pid unexpected victim_pid: actual 0 !=
>>> expected 12649
>>> test_oom_policy:FAIL:victim_cgid unexpected victim_cgid: actual 0 !=
>>> expected 9583
>>> test_oom_policy:FAIL:failed_cnt unexpected failed_cnt: actual 0 !=
>>> expected 1
>>> #154     oom_policy:FAIL
>>> Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
>>> Successfully unloaded bpf_testmod.ko.
>>>
>>>
>> It seems that OOM is not invoked in your environment(you can check it in
>> demsg). If the memcg OOM is invoked by the test, we would record the
>> *victim_pid* and *victim_cgid* and they would not be zero. I guess the
>> reason is memory_control is not enabled in cgroup
>> "/mnt/cgroup-test-work-dir23054/", because I see the error message:
>> (cgroup_helpers.c:130: errno: No such file or directory) Opening
>>> /mnt/cgroup-test-work-dir23054//memory.max
> 
> Right, but after I set up unified cgroup hierarchy and rebooted, that
> message disappeared and cgroup setup succeeded, _but_ the test still
> failed with 0 victim_pid/cgid.  I see nothing OOM-related in dmesg, but
> the toplevel cgroupv2 cgroup.controllers file contains:
> 
> cpuset cpu io memory hugetlb pids rdma
>

Dose the toplevel cgroupv2's *cgroup.subtree_control* looks like that?
/sys/fs/cgroup$ cat cgroup.subtree_control

	cpuset cpu io memory hugetlb pids

This prog test would mkdir a test cgroup dir under the toplevel's 
cgroupv2 and rmdir after the test finishing. In my env, the test cgroup 
path looks like:

/sys/fs/cgroup/cgroup-test-work-dirxxx/

This test would run in cgroup-test-work-dirxxx.

If we want to enable memory controller in cgroup-test-work-dirxxx, we 
should guarantee that /sys/fs/cgroup/cgroup.subtree_control contanins
"memory".


> Is there something else that needs to be done to enable OOM scanning?
> I see the oom_reaper process:
> 
> root          72       2  0 11:30 ?        00:00:00 [oom_reaper]
> 
> 
> This test will need to pass BPF CI, so any assumptions about
> configuration need to be ironed out. For example, I think you should
> probably have
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
> b/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
> index bea61ff22603..54fdb8a59816 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_oom_policy.c
> @@ -109,6 +109,7 @@ void test_oom_policy(void)
>          if (!ASSERT_EQ(err, 0, "prepare cgroup env"))
>                  goto cleanup;
> 
> +       write_cgroup_file("/", "cgroup.subtree_control", "+memory");
>          write_cgroup_file("/", "memory.max", "10M");

Yes, you are right. We do need something to guarantee that the memory 
controller is enabled in cgroup-test-work-dir.
	write_cgroup_file("/", "cgroup.subtree_control", "+memory");
This code actually dose something like:

echo "+memory" > /sys/fs/cgroup/cgroup-test-work-dir/cgroup.subtree_control

What we need actually is
echo "+memory" > /sys/fs/cgroup/cgroup.subtree_control

Thanks!
>
>          /*
> 
> ...to be safe, since
> 
> https://docs.kernel.org/admin-guide/cgroup-v2.html#organizing-processes-and-threads
> 
> ...says
> 
> "No controller is enabled by default. Controllers can be enabled and
> disabled by writing to the "cgroup.subtree_control" file:
> 
> # echo "+cpu +memory -io" > cgroup.subtree_control
> 
> "
> 
> Are there any other aspects of configuration like that which might
> explain why the test passes for you but fails for me?
> 
> Alan

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