linux-kernel - Re: [PATCH bpf-next v2 5/7] mm: introduce BPF kfunc to access memory events

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Message-ID: <CAADnVQJo3HspB9-_R5yWKWLdExDmFayDpNZ4JnoBpCw6aRNTrA@mail.gmail.com>
Date: Sun, 21 Dec 2025 16:49:46 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: bpf <bpf@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, 
	LKML <linux-kernel@...r.kernel.org>, JP Kobryn <inwardvessel@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Michal Hocko <mhocko@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH bpf-next v2 5/7] mm: introduce BPF kfunc to access memory events

On Fri, Dec 19, 2025 at 6:13 PM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
>
> From: JP Kobryn <inwardvessel@...il.com>
>
> Introduce BPF kfunc to access memory events, e.g.:
> MEMCG_LOW, MEMCG_MAX, MEMCG_OOM, MEMCG_OOM_KILL etc.
>
> Signed-off-by: JP Kobryn <inwardvessel@...il.com>
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
>  mm/bpf_memcontrol.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
> index d84fe6f3ed43..858eb43766ce 100644
> --- a/mm/bpf_memcontrol.c
> +++ b/mm/bpf_memcontrol.c
> @@ -103,6 +103,22 @@ __bpf_kfunc unsigned long bpf_mem_cgroup_usage(struct mem_cgroup *memcg)
>         return mem_cgroup_usage(memcg, false) * PAGE_SIZE;
>  }
>
> +/**
> + * bpf_mem_cgroup_memory_events - Read memory cgroup's memory event value
> + * @memcg: memory cgroup
> + * @event: memory event id
> + *
> + * Returns current memory event count.
> + */
> +__bpf_kfunc unsigned long bpf_mem_cgroup_memory_events(struct mem_cgroup *memcg,
> +                                               enum memcg_memory_event event)
> +{
> +       if (event >= MEMCG_NR_MEMORY_EVENTS)
> +               return (unsigned long)-1;
> +
> +       return atomic_long_read(&memcg->memory_events[event]);
> +}

Why is patch 5 not squashed with patch 4?
I'd think placing bpf_mem_cgroup_memory_events()
right next to bpf_mem_cgroup_vm_events() in the same patch
will make the difference more clear.
For non-mm people the names are very close and on the first glance
it looks like a duplicate.