linux-kernel - Re: [PATCH v2 0/2] memcg: reading memcg stats more efficiently

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Message-ID: <87wm4v7isj.fsf@linux.dev>
Date: Wed, 15 Oct 2025 18:10:52 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: JP Kobryn <inwardvessel@...il.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,  andrii@...nel.org,
  ast@...nel.org,  mkoutny@...e.com,  yosryahmed@...gle.com,
  hannes@...xchg.org,  tj@...nel.org,  akpm@...ux-foundation.org,
  linux-kernel@...r.kernel.org,  cgroups@...r.kernel.org,
  linux-mm@...ck.org,  bpf@...r.kernel.org,  kernel-team@...a.com,
  mhocko@...nel.org,  muchun.song@...ux.dev
Subject: Re: [PATCH v2 0/2] memcg: reading memcg stats more efficiently

JP Kobryn <inwardvessel@...il.com> writes:

> On 10/15/25 1:46 PM, Shakeel Butt wrote:
>> Cc memcg maintainers.
>> On Wed, Oct 15, 2025 at 12:08:11PM -0700, JP Kobryn wrote:
>>> When reading cgroup memory.stat files there is significant kernel overhead
>>> in the formatting and encoding of numeric data into a string buffer. Beyond
>>> that, the given user mode program must decode this data and possibly
>>> perform filtering to obtain the desired stats. This process can be
>>> expensive for programs that periodically sample this data over a large
>>> enough fleet.
>>>
>>> As an alternative to reading memory.stat, introduce new kfuncs that allow
>>> fetching specific memcg stats from within cgroup iterator based bpf
>>> programs. This approach allows for numeric values to be transferred
>>> directly from the kernel to user mode via the mapped memory of the bpf
>>> program's elf data section. Reading stats this way effectively eliminates
>>> the numeric conversion work needed to be performed in both kernel and user
>>> mode. It also eliminates the need for filtering in a user mode program.
>>> i.e. where reading memory.stat returns all stats, this new approach allows
>>> returning only select stats.

It seems like I've most of these functions implemented as part of
bpfoom: https://lkml.org/lkml/2025/8/18/1403

So I definitely find them useful. Would be nice to merge our efforts.

Thanks!