On Wed, Aug 24, 2022 at 4:09 PM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > On Thu, 25 Aug 2022 at 01:07, Hao Luo <haoluo@xxxxxxxxxx> wrote: > > > > On Tue, Aug 23, 2022 at 8:01 PM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > > > > > From: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > > > > > > 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@xxxxxxxxxx> > > > Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx> > > > --- > > > > I saw this test failed on CI on s390x [0], because of using kfunc, and > > on s390x, "JIT does not support calling kernel function". Is there > > anything I can do about it > > > > You can add it to the deny list, like this patch: > https://lore.kernel.org/bpf/20220824163906.1186832-1-deso@xxxxxxxxxx Very cool! Thanks!
