Messages in this thread | | | Date | Fri, 20 May 2022 17:52:24 -0700 | Subject | Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter | From | Yonghong Song <> |
| |
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. >
| |