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Thu, 30 Oct 2025 11:20:06 -0700 (PDT) MIME-Version: 1.0 References: <20251027231727.472628-1-roman.gushchin@linux.dev> <20251027231727.472628-3-roman.gushchin@linux.dev> <87zf98xq20.fsf@linux.dev> In-Reply-To: From: Amery Hung Date: Thu, 30 Oct 2025 11:19:52 -0700 X-Gm-Features: AWmQ_bkLArZ_9Xo7aHFRx3Y_Fcg5RHa9nGJniHAp-qT8VVY1Zm9_Hwf5WmIwP68 Message-ID: Subject: Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups To: Song Liu Cc: Roman Gushchin , Andrew Morton , linux-kernel@vger.kernel.org, Alexei Starovoitov , Suren Baghdasaryan , Michal Hocko , Shakeel Butt , Johannes Weiner , Andrii Nakryiko , JP Kobryn , linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, Martin KaFai Lau , Kumar Kartikeya Dwivedi , Tejun Heo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: nn83efh4nopnynwc7p9wheppj5fpood6 X-Rspamd-Queue-Id: 7C8B514001A X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1761848407-275899 X-HE-Meta: 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 qAw/iigW NpyfnXadHYns7Ozw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 30, 2025 at 11:09=E2=80=AFAM Song Liu wrote: > > On Thu, Oct 30, 2025 at 10:22=E2=80=AFAM Roman Gushchin > wrote: > > > > Song Liu writes: > > > > > On Mon, Oct 27, 2025 at 4:17=E2=80=AFPM Roman Gushchin wrote: > > > [...] > > >> struct bpf_struct_ops_value { > > >> struct bpf_struct_ops_common_value common; > > >> @@ -1359,6 +1360,18 @@ int bpf_struct_ops_link_create(union bpf_attr= *attr) > > >> } > > >> bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_st= ruct_ops_map_lops, NULL, > > >> attr->link_create.attach_type); > > >> +#ifdef CONFIG_CGROUPS > > >> + if (attr->link_create.cgroup.relative_fd) { > > >> + struct cgroup *cgrp; > > >> + > > >> + cgrp =3D cgroup_get_from_fd(attr->link_create.cgroup= .relative_fd); > > > > > > We should use "target_fd" here, not relative_fd. > > > > > > Also, 0 is a valid fd, so we cannot use target_fd =3D=3D 0 to attach = to > > > global memcg. > > > > Yep, but then we need somehow signal there is a cgroup fd passed, > > so that struct ops'es which are not attached to cgroups keep working > > as previously. And we can't use link_create.attach_type. > > > > Should I use link_create.flags? E.g. something like add new flag > > > > @@ -1224,6 +1224,7 @@ enum bpf_perf_event_type { > > #define BPF_F_AFTER (1U << 4) > > #define BPF_F_ID (1U << 5) > > #define BPF_F_PREORDER (1U << 6) > > +#define BPF_F_CGROUP (1U << 7) > > #define BPF_F_LINK BPF_F_LINK /* 1 << 13 */ > > > > /* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the > > > > and then do something like this: > > > > int bpf_struct_ops_link_create(union bpf_attr *attr) > > { > > <...> > > if (attr->link_create.flags & BPF_F_CGROUP) { > > struct cgroup *cgrp; > > > > cgrp =3D cgroup_get_from_fd(attr->link_create.target_fd= ); > > if (IS_ERR(cgrp)) { > > err =3D PTR_ERR(cgrp); > > goto err_out; > > } > > > > link->cgroup_id =3D cgroup_id(cgrp); > > cgroup_put(cgrp); > > } > > > > Does it sound right? > > I believe adding a flag (BPF_F_CGROUP or some other name), is the > right solution for this. > > OTOH, I am not sure whether we want to add cgroup fd/id to the > bpf link. I personally prefer the model used by TCP congestion > control: the link attaches the struct_ops to a global list, then each > user picks a struct_ops from the list. But I do agree this might be > an overkill for cgroup use cases. +1. In TCP congestion control and BPF qdisc's model: During link_create, both adds the struct_ops to a list, and the struct_ops can be indexed by name. The struct_ops are not "active" by this time. Then, each has their own interface to 'apply' the struct_ops to a socket or queue: setsockopt() or netlink. But maybe cgroup-related struct_ops are different. -Amery > > Thanks, > Song >