Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Hao Luo <haoluo@google.com>
Cc: Yonghong Song <yhs@fb.com>, Tejun Heo <tj@kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Yosry Ahmed <yosryahmed@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Shuah Khan <shuah@kernel.org>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Michal Hocko <mhocko@kernel.org>,
	Stanislav Fomichev <sdf@google.com>,
	David Rientjes <rientjes@google.com>,
	Greg Thelen <gthelen@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>
Subject: Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter
Date: Mon, 23 May 2022 16:58:21 -0700	[thread overview]
Message-ID: <CAEf4BzbaHeyaHK1sChPMF=L4aQsaBGNtU+R3veqCOFz0A+svEA@mail.gmail.com> (raw)
In-Reply-To: <CA+khW7gGrwTrDsfWp7wj=QaCg01FNj381a1QLs1ThsjAkW85eQ@mail.gmail.com>

On Fri, May 20, 2022 at 7:35 PM Hao Luo <haoluo@google.com> wrote:
>
> On Fri, May 20, 2022 at 5:59 PM Yonghong Song <yhs@fb.com> wrote:
> > On 5/20/22 3:57 PM, Tejun Heo wrote:
> > > Hello,
> > >
> > > On Fri, May 20, 2022 at 03:19:19PM -0700, Alexei Starovoitov wrote:
> > >> We have bpf_map iterator that walks all bpf maps.
> > >> When map iterator is parametrized with map_fd the iterator walks
> > >> all elements of that map.
> > >> cgroup iterator should have similar semantics.
> > >> When non-parameterized it will walk all cgroups and their descendent
> > >> depth first way. I believe that's what Yonghong is proposing.
> > >> When parametrized it will start from that particular cgroup and
> > >> walk all descendant of that cgroup only.
> > >> The bpf prog can stop the iteration right away with ret 1.
> > >> Maybe we can add two parameters. One -> cgroup_fd to use and another ->
> > >> the order of iteration css_for_each_descendant_pre vs _post.
> > >> wdyt?
> > >
> > > Sounds perfectly reasonable to me.
> >
> > This works for me too. Thanks!
> >
>
> This sounds good to me. Thanks. Let's try to do it in the next iteration.

Can we, in addition to descendant_pre and descendant_post walk
algorithms also add the one that does ascendants walk (i.e., start
from specified cgroup and walk up to the root cgroup)? I don't have
specific example, but it seems natural to include it for "cgroup
iterator" in general. Hopefully it won't add much code to the
implementation.