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Date: Mon, 22 Sep 2025 16:43:28 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Michal
 Hocko <mhocko@kernel.org>, Roman Gushchin <roman.gushchin@linux.dev>,
 Muchun Song <muchun.song@linux.dev>, Alexei Starovoitov <ast@kernel.org>,
 Peilin Ye <yepeilin@google.com>, Kumar Kartikeya Dwivedi
 <memxor@gmail.com>, bpf@vger.kernel.org, linux-mm@kvack.org,
 cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team
 <kernel-team@meta.com>, Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2] memcg: skip cgroup_file_notify if spinning is not
 allowed
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References: <20250922220203.261714-1-shakeel.butt@linux.dev>
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On Mon, 22 Sep 2025 16:22:57 -0700 Shakeel Butt <shakeel.butt@linux.dev> wrote:

> > 
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2307,12 +2307,13 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
> > >  	bool drained = false;
> > >  	bool raised_max_event = false;
> > >  	unsigned long pflags;
> > > +	bool allow_spinning = gfpflags_allow_spinning(gfp_mask);
> > >  
> > 
> > Does this affect only the problematic call chain which you have
> > identified, or might other callers be undesirably affected?
> 
> It will only affect the call chain which can not spin due to possibly
> NMI context and at the moment only bpf programs can cause that.

"possibly" NMI context?  Is it possible that a bpf caller which could
have taken locks will now skip the notifications?  Or do the gfp_flags
get propagated all the way through?