Re: [PATCH 0/3] cgroup: nmi safe css_rstat_updated

[Michal Koutný]

On Mon, Jun 09, 2025 at 03:56:08PM -0700, Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote:
> BPF programs can run in nmi context and may trigger memcg charged memory
> allocation in such context. Recently linux added support to nmi safe
> page allocation along with memcg charging of such allocations. However
> the kmalloc/slab support and corresponding memcg charging is still
> lacking,
> 
> To provide nmi safe support for memcg charging for kmalloc/slab
> allocations, we need nmi safe memcg stats and for that we need nmi safe
> css_rstat_updated() which adds the given cgroup state whose stats are
> updated into the per-cpu per-ss update tree. This series took the aim to
> make css_rstat_updated() nmi safe.

memcg charging relies on page counters and per-cpu stocks.
css_rstat_updated() is "only" for statistics (which has admiteddly some
in-kernel consumers but those are already affected by batching and
flushing errors).

Have I missed some updates that make css_rstat_updated() calls critical
for memcg charging? I'd find it useful to explain this aspect more in
the cover letter.

Thanks,
Michal

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