linux-kernel - Re: [PATCH bpf-next v1 5/5] bpf: add a selftest for cgroup hierarchical stats collection

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Message-ID: <20220603162339.GA25043@blackbody.suse.cz>
Date:   Fri, 3 Jun 2022 18:23:39 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Hocko <mhocko@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH bpf-next v1 5/5] bpf: add a selftest for cgroup
 hierarchical stats collection

On Fri, May 20, 2022 at 01:21:33AM +0000, Yosry Ahmed <yosryahmed@...gle.com> wrote:
> +#define CGROUP_PATH(p, n) {.name = #n, .path = #p"/"#n}
> +
> +static struct {
> +	const char *name, *path;

Please unify the order of path and name with the macro (slightly
confusing ;-).

> +SEC("tp_btf/mm_vmscan_memcg_reclaim_end")
> +int BPF_PROG(vmscan_end, struct lruvec *lruvec, struct scan_control *sc)
> +{
> [...]
> +	struct cgroup *cgrp = task_memcg(current);
> [...]
> +	/* cgrp may not have memory controller enabled */
> +	if (!cgrp)
> +		return 0;

Yes, the controller may not be enabled (for a cgroup).
Just noting that the task_memcg() implementation will fall back to
root_mem_cgroup in such a case (or nearest ancestor), you may want to
use cgroup_ss_mask() for proper detection.

Regards,
Michal