Hi Tejun,
Thanks for your review and suggestions!
On Mon, Aug 10, 2026 at 10:00:55AM -1000, Tejun Heo wrote:
Hello,
On Fri, Aug 07, 2026 at 12:37:31PM -0700, Ziyang Men wrote:
+__bpf_kfunc struct blkcg *bpf_get_root_blkcg(void)
+__bpf_kfunc struct blkcg *bpf_get_blkcg(struct cgroup_subsys_state *css)
+__bpf_kfunc void bpf_put_blkcg(struct blkcg *blkcg)
+__bpf_kfunc void bpf_blkcg_flush_stats(struct blkcg *blkcg)
I wonder whether making the above deal with css's would make more sense so
that we don't end up with per-subsystem iterators. If casting to per-subsys
type is necessary, we can provide RCU protected cast kfucns.
Good idea! These do nothing block specific and we already have some common
helpers for it such as the bpf_get_root_blkcg(). What is missing is a way to get
one controller's css from a cgroup with a reference held, and the cast. So
I would add in kernel/cgroup/
struct cgroup_subsys_state *bpf_cgroup_css(struct cgroup *cgrp, int ssid);
void bpf_css_release(struct cgroup_subsys_state *css);
where the @ssid is an enum cgroup_subsys_id value. Afterwards, the only piece
for
blkcg left is:
struct blkcg *bpf_css_to_blkcg(struct cgroup_subsys_state *css);
Note the bpf_blkcg_flush_stats may keep its current shape as it mirrors the
blkcg_print_stat() which skips the root.
With these helpers we can also replace the existing ones in
mm/bpf_memcontrol.c as well:
bpf_get_mem_cgroup()
bpf_put_mem_cgroup()
bpf_mem_cgroup_flush_stats()
they map onto bpf_cgroup_css() plus a bpf_css_to_memcg() cast the same way.
Hi Roman, JP, Shakeel: Do you think it is worth applying above changes for
the memory controller as well? If you are happy with the direction I am glad to
send the conversion as a follow-up once the generic kfuncs are in. Would you
take it?
+__bpf_kfunc u64 bpf_blkg_iostat_bytes(struct blkcg_gq *blkg,
+ enum blkg_iostat_type rw)
+__bpf_kfunc u64 bpf_blkg_iostat_ios(struct blkcg_gq *blkg,
+ enum blkg_iostat_type rw)
+__bpf_kfunc u64 bpf_blkg_dev(struct blkcg_gq *blkg)
Ignoring 32bit split reads (do we really care for BPF accesses?), the above
can easily be done with BPF_CORE_READ(), right?
Agree, these parts will be removed in the next version.
Thanks.
--
tejun
Please let me know whether the above ideas works. Thanks very much!
Best,
Ziyang
