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bpf: rstat: cgroup hierarchical stats #3441

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bpf: rstat: cgroup hierarchical stats #3441

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Pull request for series with
subject: bpf: rstat: cgroup hierarchical stats
version: 7
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759

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Master branch: d25f40f
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

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Master branch: e19db67
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

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Master branch: 0c9a7a7
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

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Master branch: 0c9a7a7
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

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Master branch: 9e32084
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

Kernel Patches Daemon and others added 9 commits August 8, 2022 15:22
adding ci files
3125843
@bentiss
btf: Add a new kfunc flag which allows to mark a function to be sleep…
ab26f7a 
…able

This allows to declare a kfunc as sleepable and prevents its use in
a non sleepable program.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Co-developed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Hao Luo <haoluo@google.com>
@yosrym93
cgroup: enable cgroup_get_from_file() on cgroup1
97f2384 
cgroup_get_from_file() currently fails with -EBADF if called on cgroup
v1. However, the current implementation works on cgroup v1 as well, so
the restriction is unnecessary.

This enabled cgroup_get_from_fd() to work on cgroup v1, which would be
the only thing stopping bpf cgroup_iter from supporting cgroup v1.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Hao Luo <haoluo@google.com>
@haoluo1022
bpf, iter: Fix the condition on p when calling stop.
6c93596 
In bpf_seq_read, seq->op->next() could return an ERR and jump to
the label stop. However, the existing code in stop does not handle
the case when p (returned from next()) is an ERR. Adds the handling
of ERR of p by converting p into an error and jumping to done.

Because all the current implementations do not have a case that
returns ERR from next(), so this patch doesn't have behavior changes
right now.

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Hao Luo <haoluo@google.com>
@haoluo1022
bpf: Introduce cgroup iter
3351c62 
Cgroup_iter is a type of bpf_iter. It walks over cgroups in four modes:

 - walking a cgroup's descendants in pre-order.
 - walking a cgroup's descendants in post-order.
 - walking a cgroup's ancestors.
 - process only the given cgroup.

When attaching cgroup_iter, one can set a cgroup to the iter_link
created from attaching. This cgroup is passed as a file descriptor
or cgroup id and serves as the starting point of the walk. If no
cgroup is specified, the starting point will be the root cgroup v2.

For walking descendants, one can specify the order: either pre-order or
post-order. For walking ancestors, the walk starts at the specified
cgroup and ends at the root.

One can also terminate the walk early by returning 1 from the iter
program.

Note that because walking cgroup hierarchy holds cgroup_mutex, the iter
program is called with cgroup_mutex held.

Currently only one session is supported, which means, depending on the
volume of data bpf program intends to send to user space, the number
of cgroups that can be walked is limited. For example, given the current
buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
be walked is 512. This is a limitation of cgroup_iter. If the output
data is larger than the kernel buffer size, after all data in the
kernel buffer is consumed by user space, the subsequent read() syscall
will signal EOPNOTSUPP. In order to work around, the user may have to
update their program to reduce the volume of data sent to output. For
example, skip some uninteresting cgroups. In future, we may extend
bpf_iter flags to allow customizing buffer size.

Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Hao Luo <haoluo@google.com>
@haoluo1022
selftests/bpf: Test cgroup_iter.
25e309f 
Add a selftest for cgroup_iter. The selftest creates a mini cgroup tree
of the following structure:

    ROOT (working cgroup)
     |
   PARENT
  /      \
CHILD1  CHILD2

and tests the following scenarios:

 - invalid cgroup fd.
 - pre-order walk over descendants from PARENT.
 - post-order walk over descendants from PARENT.
 - walk of ancestors from PARENT.
 - walk from PARENT in the default order, which is pre-order.
 - process only a single object (i.e. PARENT).
 - early termination.

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Hao Luo <haoluo@google.com>
@yosrym93
cgroup: bpf: enable bpf programs to integrate with rstat
f7084e9 
Enable bpf programs to make use of rstat to collect cgroup hierarchical
stats efficiently:
- Add cgroup_rstat_updated() kfunc, for bpf progs that collect stats.
- Add cgroup_rstat_flush() sleepable kfunc, for bpf progs that read stats.
- Add an empty bpf_rstat_flush() hook that is called during rstat
  flushing, for bpf progs that flush stats to attach to. Attaching a bpf
  prog to this hook effectively registers it as a flush callback.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Hao Luo <haoluo@google.com>
@yosrym93
selftests/bpf: extend cgroup helpers
95f9d6d 
This patch extends bpf selft cgroup_helpers [ID] n various ways:
- Add enable_controllers() that allows tests to enable all or a
  subset of controllers for a specific cgroup.
- Add join_cgroup_parent(). The cgroup workdir is based on the pid,
  therefore a spawned child cannot join the same cgroup hierarchy of the
  test through join_cgroup(). join_cgroup_parent() is used in child
  processes to join a cgroup under the parent's workdir.
- Add write_cgroup_file() and write_cgroup_file_parent() (similar to
  join_cgroup_parent() above).
- Add get_root_cgroup() for tests that need to do checks on root cgroup.
- Distinguish relative and absolute cgroup paths in function arguments.
  Now relative paths are called relative_path, and absolute paths are
  called cgroup_path.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Hao Luo <haoluo@google.com>
@yosrym93
selftests/bpf: add a selftest for cgroup hierarchical stats collection
b5f83fd 
Add a selftest that tests the whole workflow for collecting,
aggregating (flushing), and displaying cgroup hierarchical stats.

TL;DR:
- Userspace program creates a cgroup hierarchy and induces memcg reclaim
  in parts of it.
- 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.
- Userspace program makes sure the stats are aggregated and read
  correctly.

Detailed explanation:
- The test loads tracing bpf programs, vmscan_start and vmscan_end, to
  measure the latency of cgroup reclaim. Per-cgroup readings 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).

- Finally, the test creates a cgroup hierarchy and induces memcg reclaim
  in parts of it, and makes sure that the stats collection, aggregation,
  and reading workflow works as expected.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Hao Luo <haoluo@google.com>
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Master branch: ca34ce2
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=665759
version: 7

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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=665759 irrelevant now. Closing PR.

@kernel-patches-bot kernel-patches-bot deleted the series/641705=>bpf-next branch August 9, 2022 16:26
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