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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Tue, 28 Jun 2022 00:14:33 -0700
Message-ID: <CAJD7tkZ3AEPEUD9V-5nxUgmS5SLc6qp50ZyrRoAQgdzPM=a-Hg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 8/8] bpf: add a selftest for cgroup
 hierarchical stats collection
To:     Yonghong Song <yhs@fb.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        David Rientjes <rientjes@google.com>,
        Stanislav Fomichev <sdf@google.com>,
        Greg Thelen <gthelen@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>
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On Mon, Jun 27, 2022 at 11:47 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Mon, Jun 27, 2022 at 11:14 PM Yonghong Song <yhs@fb.com> wrote:
> >
> >
> >
> > On 6/10/22 12:44 PM, Yosry Ahmed wrote:
> > > Add a selftest that tests the whole workflow for collecting,
> > > aggregating (flushing), and displaying cgroup hierarchical stats.
> > >
> > > TL;DR:
> > > - Whenever reclaim happens, vmscan_start and vmscan_end update
> > >    per-cgroup percpu readings, and tell rstat which (cgroup, cpu) pairs
> > >    have updates.
> > > - When userspace tries to read the stats, vmscan_dump calls rstat to flush
> > >    the stats, and outputs the stats in text format to userspace (similar
> > >    to cgroupfs stats).
> > > - rstat calls vmscan_flush once for every (cgroup, cpu) pair that has
> > >    updates, vmscan_flush aggregates cpu readings and propagates updates
> > >    to parents.
> > >
> > > Detailed explanation:
> > > - The test loads tracing bpf programs, vmscan_start and vmscan_end, to
> > >    measure the latency of cgroup reclaim. Per-cgroup ratings are stored in
> > >    percpu maps for efficiency. When a cgroup reading is updated on a cpu,
> > >    cgroup_rstat_updated(cgroup, cpu) is called to add the cgroup to the
> > >    rstat updated tree on that cpu.
> > >
> > > - A cgroup_iter program, vmscan_dump, is loaded and pinned to a file, for
> > >    each cgroup. Reading this file invokes the program, which calls
> > >    cgroup_rstat_flush(cgroup) to ask rstat to propagate the updates for all
> > >    cpus and cgroups that have updates in this cgroup's subtree. Afterwards,
> > >    the stats are exposed to the user. vmscan_dump returns 1 to terminate
> > >    iteration early, so that we only expose stats for one cgroup per read.
> > >
> > > - An ftrace program, vmscan_flush, is also loaded and attached to
> > >    bpf_rstat_flush. When rstat flushing is ongoing, vmscan_flush is invoked
> > >    once for each (cgroup, cpu) pair that has updates. cgroups are popped
> > >    from the rstat tree in a bottom-up fashion, so calls will always be
> > >    made for cgroups that have updates before their parents. The program
> > >    aggregates percpu readings to a total per-cgroup reading, and also
> > >    propagates them to the parent cgroup. After rstat flushing is over, all
> > >    cgroups will have correct updated hierarchical readings (including all
> > >    cpus and all their descendants).
> > >
> > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> >
> > There are a selftest failure with test:
> >
> > get_cgroup_vmscan_delay:PASS:output format 0 nsec
> > get_cgroup_vmscan_delay:PASS:cgroup_id 0 nsec
> > get_cgroup_vmscan_delay:PASS:vmscan_reading 0 nsec
> > get_cgroup_vmscan_delay:PASS:read cgroup_iter 0 nsec
> > get_cgroup_vmscan_delay:PASS:output format 0 nsec
> > get_cgroup_vmscan_delay:PASS:cgroup_id 0 nsec
> > get_cgroup_vmscan_delay:FAIL:vmscan_reading unexpected vmscan_reading:
> > actual 0 <= expected 0
> > check_vmscan_stats:FAIL:child1_vmscan unexpected child1_vmscan: actual
> > 781874 != expected 382092
> > check_vmscan_stats:FAIL:child2_vmscan unexpected child2_vmscan: actual
> > -1 != expected -2
> > check_vmscan_stats:FAIL:test_vmscan unexpected test_vmscan: actual
> > 781874 != expected 781873
> > check_vmscan_stats:FAIL:root_vmscan unexpected root_vmscan: actual 0 <
> > expected 781874
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> > destroy_progs:PASS:remove cgroup_iter root pin 0 nsec
> > cleanup_bpffs:PASS:rmdir /sys/fs/bpf/vmscan/ 0 nsec
> > #33      cgroup_hierarchical_stats:FAIL
> >
>
> The test is passing on my setup. I am trying to figure out if there is
> something outside the setup done by the test that can cause the test
> to fail.
>

I can't reproduce the failure on my machine. It seems like for some
reason reclaim is not invoked in one of the test cgroups which results
in the expected stats not being there. I have a few suspicions as to
what might cause this but I am not sure.

If you have the capacity, do you mind re-running the test with the
attached diff1.patch? (and maybe diff2.patch if that fails, this will
cause OOMs in the test cgroup, you might see some process killed
warnings).
Thanks!


> >
> > Also an existing test also failed.
> >
> > btf_dump_data:PASS:find type id 0 nsec
> >
> >
> > btf_dump_data:PASS:failed/unexpected type_sz 0 nsec
> >
> >
> > btf_dump_data:FAIL:ensure expected/actual match unexpected ensure
> > expected/actual match: actual '(union bpf_iter_link_info){.map =
> > (struct){.map_fd = (__u32)1,},.cgroup '
> > test_btf_dump_struct_data:PASS:find struct sk_buff 0 nsec
> >
>
> Yeah I see what happened there. bpf_iter_link_info was changed by the
> patch that introduced cgroup_iter, and this specific union is used by
> the test to test the "union with nested struct" btf dumping. I will
> add a patch in the next version that updates the btf_dump_data test
> accordingly. Thanks.
>
> >
> > test_btf_dump_struct_data:PASS:unexpected return value dumping sk_buff 0
> > nsec
> >
> > btf_dump_data:PASS:verify prefix match 0 nsec
> >
> >
> > btf_dump_data:PASS:find type id 0 nsec
> >
> >
> > btf_dump_data:PASS:failed to return -E2BIG 0 nsec
> >
> >
> > btf_dump_data:PASS:ensure expected/actual match 0 nsec
> >
> >
> > btf_dump_data:PASS:verify prefix match 0 nsec
> >
> >
> > btf_dump_data:PASS:find type id 0 nsec
> >
> >
> > btf_dump_data:PASS:failed to return -E2BIG 0 nsec
> >
> >
> > btf_dump_data:PASS:ensure expected/actual match 0 nsec
> >
> >
> > #21/14   btf_dump/btf_dump: struct_data:FAIL
> >
> > please take a look.
> >
> > > ---
> > >   .../prog_tests/cgroup_hierarchical_stats.c    | 351 ++++++++++++++++++
> > >   .../bpf/progs/cgroup_hierarchical_stats.c     | 234 ++++++++++++
> > >   2 files changed, 585 insertions(+)
> > >   create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > >   create mode 100644 tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
> > >
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > > new file mode 100644
> > > index 0000000000000..b78a4043da49a
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > > @@ -0,0 +1,351 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/*
> > > + * Functions to manage eBPF programs attached to cgroup subsystems
> > > + *
> > > + * Copyright 2022 Google LLC.
> > > + */
> > > +#include <errno.h>
> > > +#include <sys/types.h>
> > > +#include <sys/mount.h>
> > > +#include <sys/stat.h>
> > > +#include <unistd.h>
> > > +
> > > +#include <test_progs.h>
> > > +#include <bpf/libbpf.h>
> > > +#include <bpf/bpf.h>
> > > +
> > > +#include "cgroup_helpers.h"
> > > +#include "cgroup_hierarchical_stats.skel.h"
> > > +
> > > +#define PAGE_SIZE 4096
> > > +#define MB(x) (x << 20)
> > > +
> > > +#define BPFFS_ROOT "/sys/fs/bpf/"
> > > +#define BPFFS_VMSCAN BPFFS_ROOT"vmscan/"
> > > +
> > > +#define CG_ROOT_NAME "root"
> > > +#define CG_ROOT_ID 1
> > > +
> > > +#define CGROUP_PATH(p, n) {.path = #p"/"#n, .name = #n}
> > > +
> > > +static struct {
> > > +     const char *path, *name;
> > > +     unsigned long long id;
> > > +     int fd;
> > > +} cgroups[] = {
> > > +     CGROUP_PATH(/, test),
> > > +     CGROUP_PATH(/test, child1),
> > > +     CGROUP_PATH(/test, child2),
> > > +     CGROUP_PATH(/test/child1, child1_1),
> > > +     CGROUP_PATH(/test/child1, child1_2),
> > > +     CGROUP_PATH(/test/child2, child2_1),
> > > +     CGROUP_PATH(/test/child2, child2_2),
> > > +};
> > > +
> > > +#define N_CGROUPS ARRAY_SIZE(cgroups)
> > > +#define N_NON_LEAF_CGROUPS 3
> > > +
> > > +int root_cgroup_fd;
> > > +bool mounted_bpffs;
> > > +
> > > +static int read_from_file(const char *path, char *buf, size_t size)
> > > +{
> > > +     int fd, len;
> > > +
> > > +     fd = open(path, O_RDONLY);
> > > +     if (fd < 0) {
> > > +             log_err("Open %s", path);
> > > +             return -errno;
> > > +     }
> > > +     len = read(fd, buf, size);
> > > +     if (len < 0)
> > > +             log_err("Read %s", path);
> > > +     else
> > > +             buf[len] = 0;
> > > +     close(fd);
> > > +     return len < 0 ? -errno : 0;
> > > +}
> > > +
> > > +static int setup_bpffs(void)
> > > +{
> > > +     int err;
> > > +
> > > +     /* Mount bpffs */
> > > +     err = mount("bpf", BPFFS_ROOT, "bpf", 0, NULL);
> > > +     mounted_bpffs = !err;
> > > +     if (!ASSERT_OK(err && errno != EBUSY, "mount bpffs"))
> > > +             return err;
> > > +
> > > +     /* Create a directory to contain stat files in bpffs */
> > > +     err = mkdir(BPFFS_VMSCAN, 0755);
> > > +     ASSERT_OK(err, "mkdir bpffs");
> > > +     return err;
> > > +}
> > > +
> > > +static void cleanup_bpffs(void)
> > > +{
> > > +     /* Remove created directory in bpffs */
> > > +     ASSERT_OK(rmdir(BPFFS_VMSCAN), "rmdir "BPFFS_VMSCAN);
> > > +
> > > +     /* Unmount bpffs, if it wasn't already mounted when we started */
> > > +     if (mounted_bpffs)
> > > +             return;
> > > +     ASSERT_OK(umount(BPFFS_ROOT), "unmount bpffs");
> > > +}
> > > +
> > > +static int setup_cgroups(void)
> > > +{
> > > +     int i, fd, err;
> > > +
> > > +     err = setup_cgroup_environment();
> > > +     if (!ASSERT_OK(err, "setup_cgroup_environment"))
> > > +             return err;
> > > +
> > > +     root_cgroup_fd = get_root_cgroup();
> > > +     if (!ASSERT_GE(root_cgroup_fd, 0, "get_root_cgroup"))
> > > +             return root_cgroup_fd;
> > > +
> > > +     for (i = 0; i < N_CGROUPS; i++) {
> > > +             fd = create_and_get_cgroup(cgroups[i].path);
> > > +             if (!ASSERT_GE(fd, 0, "create_and_get_cgroup"))
> > > +                     return fd;
> > > +
> > > +             cgroups[i].fd = fd;
> > > +             cgroups[i].id = get_cgroup_id(cgroups[i].path);
> > > +
> > > +             /*
> > > +              * Enable memcg controller for the entire hierarchy.
> > > +              * Note that stats are collected for all cgroups in a hierarchy
> > > +              * with memcg enabled anyway, but are only exposed for cgroups
> > > +              * that have memcg enabled.
> > > +              */
> > > +             if (i < N_NON_LEAF_CGROUPS) {
> > > +                     err = enable_controllers(cgroups[i].path, "memory");
> > > +                     if (!ASSERT_OK(err, "enable_controllers"))
> > > +                             return err;
> > > +             }
> > > +     }
> > > +     return 0;
> > > +}
> > > +
> > > +static void cleanup_cgroups(void)
> > > +{
> > > +     close(root_cgroup_fd);
> > > +     for (int i = 0; i < N_CGROUPS; i++)
> > > +             close(cgroups[i].fd);
> > > +     cleanup_cgroup_environment();
> > > +}
> > > +
> > > +
> > > +static int setup_hierarchy(void)
> > > +{
> > > +     return setup_bpffs() || setup_cgroups();
> > > +}
> > > +
> > > +static void destroy_hierarchy(void)
> > > +{
> > > +     cleanup_cgroups();
> > > +     cleanup_bpffs();
> > > +}
> > > +
> > > +static void alloc_anon(size_t size)
> > > +{
> > > +     char *buf, *ptr;
> > > +
> > > +     buf = malloc(size);
> > > +     for (ptr = buf; ptr < buf + size; ptr += PAGE_SIZE)
> > > +             *ptr = 0;
> > > +     free(buf);
> > > +}
> > > +
> > > +static int induce_vmscan(void)
> > > +{
> > > +     char size[128];
> > > +     int i, err;
> > > +
> > > +     /*
> > > +      * Set memory.high for test parent cgroup to 1 MB to throttle
> > > +      * allocations and invoke reclaim in children.
> > > +      */
> > > +     snprintf(size, 128, "%d", MB(1));
> > > +     err = write_cgroup_file(cgroups[0].path, "memory.high", size);
> > > +     if (!ASSERT_OK(err, "write memory.high"))
> > > +             return err;
> > > +     /*
> > > +      * In every leaf cgroup, run a memory hog for a few seconds to induce
> > > +      * reclaim then kill it.
> > > +      */
> > > +     for (i = N_NON_LEAF_CGROUPS; i < N_CGROUPS; i++) {
> > > +             pid_t pid = fork();
> > > +
> > > +             if (pid == 0) {
> > > +                     /* Join cgroup in the parent process workdir */
> > > +                     join_parent_cgroup(cgroups[i].path);
> > > +
> > > +                     /* Allocate more memory than memory.high */
> > > +                     alloc_anon(MB(2));
> > > +                     exit(0);
> > > +             } else {
> > > +                     /* Wait for child to cause reclaim then kill it */
> > > +                     if (!ASSERT_GT(pid, 0, "fork"))
> > > +                             return pid;
> > > +                     sleep(2);
> > > +                     kill(pid, SIGKILL);
> > > +                     waitpid(pid, NULL, 0);
> > > +             }
> > > +     }
> > > +     return 0;
> > > +}
> > > +
> > > +static unsigned long long get_cgroup_vmscan_delay(unsigned long long cgroup_id,
> > > +                                               const char *file_name)
> > > +{
> > > +     char buf[128], path[128];
> > > +     unsigned long long vmscan = 0, id = 0;
> > > +     int err;
> > > +
> > > +     /* For every cgroup, read the file generated by cgroup_iter */
> > > +     snprintf(path, 128, "%s%s", BPFFS_VMSCAN, file_name);
> > > +     err = read_from_file(path, buf, 128);
> > > +     if (!ASSERT_OK(err, "read cgroup_iter"))
> > > +             return 0;
> > > +
> > > +     /* Check the output file formatting */
> > > +     ASSERT_EQ(sscanf(buf, "cg_id: %llu, total_vmscan_delay: %llu\n",
> > > +                      &id, &vmscan), 2, "output format");
> > > +
> > > +     /* Check that the cgroup_id is displayed correctly */
> > > +     ASSERT_EQ(id, cgroup_id, "cgroup_id");
> > > +     /* Check that the vmscan reading is non-zero */
> > > +     ASSERT_GT(vmscan, 0, "vmscan_reading");
> > > +     return vmscan;
> > > +}
> > > +
> > > +static void check_vmscan_stats(void)
> > > +{
> > > +     int i;
> > > +     unsigned long long vmscan_readings[N_CGROUPS], vmscan_root;
> > > +
> > > +     for (i = 0; i < N_CGROUPS; i++)
> > > +             vmscan_readings[i] = get_cgroup_vmscan_delay(cgroups[i].id,
> > > +                                                          cgroups[i].name);
> > > +
> > > +     /* Read stats for root too */
> > > +     vmscan_root = get_cgroup_vmscan_delay(CG_ROOT_ID, CG_ROOT_NAME);
> > > +
> > > +     /* Check that child1 == child1_1 + child1_2 */
> > > +     ASSERT_EQ(vmscan_readings[1], vmscan_readings[3] + vmscan_readings[4],
> > > +               "child1_vmscan");
> > > +     /* Check that child2 == child2_1 + child2_2 */
> > > +     ASSERT_EQ(vmscan_readings[2], vmscan_readings[5] + vmscan_readings[6],
> > > +               "child2_vmscan");
> > > +     /* Check that test == child1 + child2 */
> > > +     ASSERT_EQ(vmscan_readings[0], vmscan_readings[1] + vmscan_readings[2],
> > > +               "test_vmscan");
> > > +     /* Check that root >= test */
> > > +     ASSERT_GE(vmscan_root, vmscan_readings[1], "root_vmscan");
> > > +}
> > > +
> > > +static int setup_cgroup_iter(struct cgroup_hierarchical_stats *obj, int cgroup_fd,
> > > +                          const char *file_name)
> > > +{
> > > +     DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
> > > +     union bpf_iter_link_info linfo = {};
> > > +     struct bpf_link *link;
> > > +     char path[128];
> > > +     int err;
> > > +
> > > +     /*
> > > +      * Create an iter link, parameterized by cgroup_fd.
> > > +      * We only want to traverse one cgroup, so set the traversal order to
> > > +      * "pre", and return 1 from dump_vmscan to stop iteration after the
> > > +      * first cgroup.
> > > +      */
> > > +     linfo.cgroup.cgroup_fd = cgroup_fd;
> > > +     linfo.cgroup.traversal_order = BPF_ITER_CGROUP_PRE;
> > > +     opts.link_info = &linfo;
> > > +     opts.link_info_len = sizeof(linfo);
> > > +     link = bpf_program__attach_iter(obj->progs.dump_vmscan, &opts);
> > > +     if (!ASSERT_OK_PTR(link, "attach iter"))
> > > +             return libbpf_get_error(link);
> > > +
> > > +     /* Pin the link to a bpffs file */
> > > +     snprintf(path, 128, "%s%s", BPFFS_VMSCAN, file_name);
> > > +     err = bpf_link__pin(link, path);
> > > +     ASSERT_OK(err, "pin cgroup_iter");
> > > +     return err;
> > > +}
> > > +
> > > +static int setup_progs(struct cgroup_hierarchical_stats **skel)
> > > +{
> > > +     int i, err;
> > > +     struct bpf_link *link;
> > > +     struct cgroup_hierarchical_stats *obj;
> > > +
> > > +     obj = cgroup_hierarchical_stats__open_and_load();
> > > +     if (!ASSERT_OK_PTR(obj, "open_and_load"))
> > > +             return libbpf_get_error(obj);
> > > +
> > > +     /* Attach cgroup_iter program that will dump the stats to cgroups */
> > > +     for (i = 0; i < N_CGROUPS; i++) {
> > > +             err = setup_cgroup_iter(obj, cgroups[i].fd, cgroups[i].name);
> > > +             if (!ASSERT_OK(err, "setup_cgroup_iter"))
> > > +                     return err;
> > > +     }
> > > +     /* Also dump stats for root */
> > > +     err = setup_cgroup_iter(obj, root_cgroup_fd, CG_ROOT_NAME);
> > > +     if (!ASSERT_OK(err, "setup_cgroup_iter"))
> > > +             return err;
> > > +
> > > +     /* Attach rstat flusher */
> > > +     link = bpf_program__attach(obj->progs.vmscan_flush);
> > > +     if (!ASSERT_OK_PTR(link, "attach rstat"))
> > > +             return libbpf_get_error(link);
> > > +
> > > +     /* Attach tracing programs that will calculate vmscan delays */
> > > +     link = bpf_program__attach(obj->progs.vmscan_start);
> > > +     if (!ASSERT_OK_PTR(obj, "attach raw_tracepoint"))
> > > +             return libbpf_get_error(obj);
> > > +
> > > +     link = bpf_program__attach(obj->progs.vmscan_end);
> > > +     if (!ASSERT_OK_PTR(obj, "attach raw_tracepoint"))
> > > +             return libbpf_get_error(obj);
> > > +
> > > +     *skel = obj;
> > > +     return 0;
> > > +}
> > > +
> > > +void destroy_progs(struct cgroup_hierarchical_stats *skel)
> > > +{
> > > +     char path[128];
> > > +     int i;
> > > +
> > > +     for (i = 0; i < N_CGROUPS; i++) {
> > > +             /* Delete files in bpffs that cgroup_iters are pinned in */
> > > +             snprintf(path, 128, "%s%s", BPFFS_VMSCAN,
> > > +                      cgroups[i].name);
> > > +             ASSERT_OK(remove(path), "remove cgroup_iter pin");
> > > +     }
> > > +
> > > +     /* Delete root file in bpffs */
> > > +     snprintf(path, 128, "%s%s", BPFFS_VMSCAN, CG_ROOT_NAME);
> > > +     ASSERT_OK(remove(path), "remove cgroup_iter root pin");
> > > +     cgroup_hierarchical_stats__destroy(skel);
> > > +}
> > > +
> > > +void test_cgroup_hierarchical_stats(void)
> > > +{
> > > +     struct cgroup_hierarchical_stats *skel = NULL;
> > > +
> > > +     if (setup_hierarchy())
> > > +             goto hierarchy_cleanup;
> > > +     if (setup_progs(&skel))
> > > +             goto cleanup;
> > > +     if (induce_vmscan())
> > > +             goto cleanup;
> > > +     check_vmscan_stats();
> > > +cleanup:
> > > +     destroy_progs(skel);
> > > +hierarchy_cleanup:
> > > +     destroy_hierarchy();
> > > +}
> > > diff --git a/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
> > > new file mode 100644
> > > index 0000000000000..fd2028f1ed70b
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
> > > @@ -0,0 +1,234 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/*
> > > + * Functions to manage eBPF programs attached to cgroup subsystems
> > > + *
> > > + * Copyright 2022 Google LLC.
> > > + */
> > > +#include "vmlinux.h"
> > > +#include <bpf/bpf_helpers.h>
> > > +#include <bpf/bpf_tracing.h>
> > > +
> > > +char _license[] SEC("license") = "GPL";
> > > +
> > > +/*
> > > + * Start times are stored per-task, not per-cgroup, as multiple tasks in one
> > > + * cgroup can perform reclain concurrently.
> > > + */
> > > +struct {
> > > +     __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
> > > +     __uint(map_flags, BPF_F_NO_PREALLOC);
> > > +     __type(key, int);
> > > +     __type(value, __u64);
> > > +} vmscan_start_time SEC(".maps");
> > > +
> > > +struct vmscan_percpu {
> > > +     /* Previous percpu state, to figure out if we have new updates */
> > > +     __u64 prev;
> > > +     /* Current percpu state */
> > > +     __u64 state;
> > > +};
> > > +
> > > +struct vmscan {
> > > +     /* State propagated through children, pending aggregation */
> > > +     __u64 pending;
> > > +     /* Total state, including all cpus and all children */
> > > +     __u64 state;
> > > +};
> > > +
> > > +struct {
> > > +     __uint(type, BPF_MAP_TYPE_PERCPU_HASH);
> > > +     __uint(max_entries, 10);
> > > +     __type(key, __u64);
> > > +     __type(value, struct vmscan_percpu);
> > > +} pcpu_cgroup_vmscan_elapsed SEC(".maps");
> > > +
> > > +struct {
> > > +     __uint(type, BPF_MAP_TYPE_HASH);
> > > +     __uint(max_entries, 10);
> > > +     __type(key, __u64);
> > > +     __type(value, struct vmscan);
> > > +} cgroup_vmscan_elapsed SEC(".maps");
> > > +
> > > +extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __ksym;
> > > +extern void cgroup_rstat_flush(struct cgroup *cgrp) __ksym;
> > > +
> > > +static inline struct cgroup *task_memcg(struct task_struct *task)
> > > +{
> > > +     return task->cgroups->subsys[memory_cgrp_id]->cgroup;
> > > +}
> > > +
> > > +static inline uint64_t cgroup_id(struct cgroup *cgrp)
> > > +{
> > > +     return cgrp->kn->id;
> > > +}
> > > +
> > > +static inline int create_vmscan_percpu_elem(__u64 cg_id, __u64 state)
> > > +{
> > > +     struct vmscan_percpu pcpu_init = {.state = state, .prev = 0};
> > > +
> > > +     if (bpf_map_update_elem(&pcpu_cgroup_vmscan_elapsed, &cg_id,
> > > +                             &pcpu_init, BPF_NOEXIST)) {
> > > +             bpf_printk("failed to create pcpu entry for cgroup %llu\n"
> > > +                        , cg_id);
> > > +             return 1;
> > > +     }
> > > +     return 0;
> > > +}
> > > +
> > > +static inline int create_vmscan_elem(__u64 cg_id, __u64 state, __u64 pending)
> > > +{
> > > +     struct vmscan init = {.state = state, .pending = pending};
> > > +
> > > +     if (bpf_map_update_elem(&cgroup_vmscan_elapsed, &cg_id,
> > > +                             &init, BPF_NOEXIST)) {
> > > +             bpf_printk("failed to create entry for cgroup %llu\n"
> > > +                        , cg_id);
> > > +             return 1;
> > > +     }
> > > +     return 0;
> > > +}
> > > +
> > > +SEC("tp_btf/mm_vmscan_memcg_reclaim_begin")
> > > +int BPF_PROG(vmscan_start, struct lruvec *lruvec, struct scan_control *sc)
> > > +{
> > > +     struct task_struct *task = bpf_get_current_task_btf();
> > > +     __u64 *start_time_ptr;
> > > +
> > > +     start_time_ptr = bpf_task_storage_get(&vmscan_start_time, task, 0,
> > > +                                       BPF_LOCAL_STORAGE_GET_F_CREATE);
> > > +     if (!start_time_ptr) {
> > > +             bpf_printk("error retrieving storage\n");
> > > +             return 0;
> > > +     }
> > > +
> > > +     *start_time_ptr = bpf_ktime_get_ns();
> > > +     return 0;
> > > +}
> > > +
> > > +SEC("tp_btf/mm_vmscan_memcg_reclaim_end")
> > > +int BPF_PROG(vmscan_end, struct lruvec *lruvec, struct scan_control *sc)
> > > +{
> > > +     struct vmscan_percpu *pcpu_stat;
> > > +     struct task_struct *current = bpf_get_current_task_btf();
> > > +     struct cgroup *cgrp;
> > > +     __u64 *start_time_ptr;
> > > +     __u64 current_elapsed, cg_id;
> > > +     __u64 end_time = bpf_ktime_get_ns();
> > > +
> > > +     /*
> > > +      * cgrp is the first parent cgroup of current that has memcg enabled in
> > > +      * its subtree_control, or NULL if memcg is disabled in the entire tree.
> > > +      * In a cgroup hierarchy like this:
> > > +      *                               a
> > > +      *                              / \
> > > +      *                             b   c
> > > +      *  If "a" has memcg enabled, while "b" doesn't, then processes in "b"
> > > +      *  will accumulate their stats directly to "a". This makes sure that no
> > > +      *  stats are lost from processes in leaf cgroups that don't have memcg
> > > +      *  enabled, but only exposes stats for cgroups that have memcg enabled.
> > > +      */
> > > +     cgrp = task_memcg(current);
> > > +     if (!cgrp)
> > > +             return 0;
> > > +
> > > +     cg_id = cgroup_id(cgrp);
> > > +     start_time_ptr = bpf_task_storage_get(&vmscan_start_time, current, 0,
> > > +                                           BPF_LOCAL_STORAGE_GET_F_CREATE);
> > > +     if (!start_time_ptr) {
> > > +             bpf_printk("error retrieving storage local storage\n");
> > > +             return 0;
> > > +     }
> > > +
> > > +     current_elapsed = end_time - *start_time_ptr;
> > > +     pcpu_stat = bpf_map_lookup_elem(&pcpu_cgroup_vmscan_elapsed,
> > > +                                     &cg_id);
> > > +     if (pcpu_stat)
> > > +             __sync_fetch_and_add(&pcpu_stat->state, current_elapsed);
> > > +     else
> > > +             create_vmscan_percpu_elem(cg_id, current_elapsed);
> > > +
> > > +     cgroup_rstat_updated(cgrp, bpf_get_smp_processor_id());
> > > +     return 0;
> > > +}
> > > +
> > > +SEC("fentry/bpf_rstat_flush")
> > > +int BPF_PROG(vmscan_flush, struct cgroup *cgrp, struct cgroup *parent, int cpu)
> > > +{
> > > +     struct vmscan_percpu *pcpu_stat;
> > > +     struct vmscan *total_stat, *parent_stat;
> > > +     __u64 cg_id = cgroup_id(cgrp);
> > > +     __u64 parent_cg_id = parent ? cgroup_id(parent) : 0;
> > > +     __u64 *pcpu_vmscan;
> > > +     __u64 state;
> > > +     __u64 delta = 0;
> > > +
> > > +     /* Add CPU changes on this level since the last flush */
> > > +     pcpu_stat = bpf_map_lookup_percpu_elem(&pcpu_cgroup_vmscan_elapsed,
> > > +                                            &cg_id, cpu);
> > > +     if (pcpu_stat) {
> > > +             state = pcpu_stat->state;
> > > +             delta += state - pcpu_stat->prev;
> > > +             pcpu_stat->prev = state;
> > > +     }
> > > +
> > > +     total_stat = bpf_map_lookup_elem(&cgroup_vmscan_elapsed, &cg_id);
> > > +     if (!total_stat) {
> > > +             create_vmscan_elem(cg_id, delta, 0);
> > > +             goto update_parent;
> > > +     }
> > > +
> > > +     /* Collect pending stats from subtree */
> > > +     if (total_stat->pending) {
> > > +             delta += total_stat->pending;
> > > +             total_stat->pending = 0;
> > > +     }
> > > +
> > > +     /* Propagate changes to this cgroup's total */
> > > +     total_stat->state += delta;
> > > +
> > > +update_parent:
> > > +     /* Skip if there are no changes to propagate, or no parent */
> > > +     if (!delta || !parent_cg_id)
> > > +             return 0;
> > > +
> > > +     /* Propagate changes to cgroup's parent */
> > > +     parent_stat = bpf_map_lookup_elem(&cgroup_vmscan_elapsed,
> > > +                                       &parent_cg_id);
> > > +     if (parent_stat)
> > > +             parent_stat->pending += delta;
> > > +     else
> > > +             create_vmscan_elem(parent_cg_id, 0, delta);
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +SEC("iter.s/cgroup")
> > > +int BPF_PROG(dump_vmscan, struct bpf_iter_meta *meta, struct cgroup *cgrp)
> > > +{
> > > +     struct seq_file *seq = meta->seq;
> > > +     struct vmscan *total_stat;
> > > +     __u64 cg_id = cgroup_id(cgrp);
> > > +
> > > +     /* Do nothing for the terminal call */
> > > +     if (!cgrp)
> > > +             return 1;
> > > +
> > > +     /* Flush the stats to make sure we get the most updated numbers */
> > > +     cgroup_rstat_flush(cgrp);
> > > +
> > > +     total_stat = bpf_map_lookup_elem(&cgroup_vmscan_elapsed, &cg_id);
> > > +     if (!total_stat) {
> > > +             bpf_printk("error finding stats for cgroup %llu\n", cg_id);
> > > +             BPF_SEQ_PRINTF(seq, "cg_id: %llu, total_vmscan_delay: -1\n",
> > > +                            cg_id);
> > > +             return 1;
> > > +     }
> > > +     BPF_SEQ_PRINTF(seq, "cg_id: %llu, total_vmscan_delay: %llu\n",
> > > +                    cg_id, total_stat->state);
> > > +
> > > +     /*
> > > +      * We only dump stats for one cgroup here, so return 1 to stop
> > > +      * iteration after the first cgroup.
> > > +      */
> > > +     return 1;
> > > +}

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