linux-kernel - Re: [PATCH v4 0/5] memcg: nmi-safe kmem charging

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Message-ID: <y2eqzgsplnp2fuvlhwk3hogffgjh3d2caohxuwa4dgt7ecznhx@m57r5xhglzyb>
Date: Mon, 2 Jun 2025 07:54:20 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Michal Koutný <mkoutny@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Vlastimil Babka <vbabka@...e.cz>, Alexei Starovoitov <ast@...nel.org>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Harry Yoo <harry.yoo@...cle.com>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>, Peter Zijlstra <peterz@...radead.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Tejun Heo <tj@...nel.org>, bpf@...r.kernel.org, 
	linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v4 0/5] memcg: nmi-safe kmem charging

On Mon, Jun 02, 2025 at 04:45:31PM +0200, Michal Koutný wrote:
> Hello Shakeel.
> 
> On Sun, May 18, 2025 at 11:31:37PM -0700, Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> > Users can attached their BPF programs at arbitrary execution points in
> > the kernel and such BPF programs may run in nmi context. In addition,
> > these programs can trigger memcg charged kernel allocations in the nmi
> > context. However memcg charging infra for kernel memory is not equipped
> > to handle nmi context for all architectures.
> 
> How much memory does this refer to? Is it unbound (in particular for
> non-privileged eBPF)? Or is it rather negligible? (I assume the former
> to make the series worth it.)
> 

It depends on the BPF program and thus can be arbitrarily large. So,
irrespective of privileged or non-privileged BPF programs, they can
allocate large amount of memory to maintain monitoring or debugging (or
for some other use-case) information.