linux-kernel - Re: [PATCH v2 10/23] mm: introduce BPF kfuncs to access memcg statistics and events

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Message-Id: <45ee5e2e857a2e4022eb380f854d2a7cf27f3ec97d75a0200b46be95ae921d3b@mail.kernel.org>
Date: Mon, 27 Oct 2025 23:48:14 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: roman.gushchin@...ux.dev,akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,ast@...nel.org,surenb@...gle.com,mhocko@...nel.org,shakeel.butt@...ux.dev,hannes@...xchg.org,andrii@...nel.org,inwardvessel@...il.com,linux-mm@...ck.org,cgroups@...r.kernel.org,bpf@...r.kernel.org,martin.lau@...nel.org,song@...nel.org,memxor@...il.com,tj@...nel.org,roman.gushchin@...ux.dev,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH v2 10/23] mm: introduce BPF kfuncs to access memcg statistics and events


```
commit 96abfe0549713749f00e32bff919a759db284a58
Author: Roman Gushchin <roman.gushchin@...ux.dev>

mm: introduce BPF kfuncs to access memcg statistics and events

This patch adds four new BPF kfuncs for accessing memory cgroup statistics
and events, making them available to all BPF program types for implementing
OOM policies and accelerating memcg data access.

> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 39a6c7c87..b9e08dddd 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h

[ ... ]

> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
> index 76c342318..387255b8a 100644
> --- a/mm/bpf_memcontrol.c
> +++ b/mm/bpf_memcontrol.c

[ ... ]

> @@ -75,6 +75,56 @@ __bpf_kfunc void bpf_put_mem_cgroup(struct mem_cgroup *memcg)
>  	css_put(&memcg->css);
>  }
>
> +/**
> + * bpf_mem_cgroup_vm_events - Read memory cgroup's vm event counter
> + * @memcg: memory cgroup
> + * @event: event id
> + *
> + * Allows to read memory cgroup event counters.
> + */
> +__bpf_kfunc unsigned long bpf_mem_cgroup_vm_events(struct mem_cgroup *memcg,
> +						enum vm_event_item event)
> +{
> +	return memcg_events(memcg, event);
> +}
> +
> +/**
> + * bpf_mem_cgroup_usage - Read memory cgroup's usage
> + * @memcg: memory cgroup
> + *
> + * Returns current memory cgroup size in bytes.
> + */
> +__bpf_kfunc unsigned long bpf_mem_cgroup_usage(struct mem_cgroup *memcg)
> +{
> +	return page_counter_read(&memcg->memory);
> +}
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The documentation says this returns bytes, but page_counter_read() returns
pages. In mm/memcontrol-v1.c, the existing mem_cgroup_usage() function's
return value is multiplied by PAGE_SIZE to convert to bytes:

    return (u64)mem_cgroup_usage(memcg, false) * PAGE_SIZE;

Should this function multiply the result by PAGE_SIZE to match its
documentation, or should the documentation be updated to say it returns
pages?

> +
> +/**
> + * bpf_mem_cgroup_page_state - Read memory cgroup's page state counter
> + * @memcg: memory cgroup
> + * @idx: counter idx
> + *
> + * Allows to read memory cgroup statistics. The output is in bytes.
> + */
> +__bpf_kfunc unsigned long bpf_mem_cgroup_page_state(struct mem_cgroup *memcg, int idx)
> +{
> +	if (idx < 0 || idx >= MEMCG_NR_STAT)
> +		return (unsigned long)-1;
> +
> +	return memcg_page_state_output(memcg, idx);
> +}

[ ... ]


```

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

In-Reply-To-Subject: `mm: introduce BPF kfuncs to access memcg statistics and events`
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/18859027430