88886309d2
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> Link: https://lore.kernel.org/r/20220824233117.1312810-6-haoluo@google.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.