On 5/20/22 9:45 AM, Tejun Heo wrote:
Hello, Yonghong. On Fri, May 20, 2022 at 09:29:43AM -0700, Yonghong Song wrote:Maybe you can have a bpf program signature like below: int BPF_PROG(dump_vmscan, struct bpf_iter_meta *meta, struct cgroup *cgrp, struct cgroup *parent_cgrp) parent_cgrp is NULL when cgrp is the root cgroup. I would like the bpf program should send the following information to user space: <parent cgroup dir name> <current cgroup dir name>I don't think parent cgroup dir name would be sufficient to reconstruct the path given that multiple cgroups in different subtrees can have the same name. For live cgroups, userspace can find the path from id (or ino) without traversing anything by constructing the fhandle, open it open_by_handle_at() and then reading /proc/self/fd/$FD symlink - https://lkml.org/lkml/2020/12/2/1126. This isn't available for dead cgroups but I'm not sure how much that'd matter given that they aren't visible from userspace anyway.
passing id/ino to user space and then get directory name in userspace should work just fine.
<various stats interested by the user> This way, user space can easily construct the cgroup hierarchy stat like cpu mem cpu pressure mem pressure ... cgroup1 ... child1 ... grandchild1 ... child2 ... cgroup 2 ... child 3 ... ... ... the bpf iterator can have additional parameter like cgroup_id = ... to only call bpf program once with that cgroup_id if specified. The kernel part of cgroup_iter can call cgroup_rstat_flush() before calling cgroup_iter bpf program. WDYT?Would it work to just pass in @cgrp and provide a group of helpers so that the program can do whatever it wanna do including looking up the full path and passing that to userspace?
I am not super familiar with cgroup internals, I guess with cgroup + helpers to retrieve stats, or directly expose stats data structure
to bpf program. Either one is okay to me as long as we can get desired results.
Thanks.
