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charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: E110540002 X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: 8c43jorxfgi33n5mbf5zcfcbs3sqrn66 X-HE-Tag: 1786489086-564248 X-HE-Meta: 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 Z4qGpun+ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 11, 2026, David Woodhouse wrote: > On Tue, 2026-08-11 at 22:21 +0200, Paolo Bonzini wrote: > >=20 > > for_each_present_cpu(cpu) > > =C2=A0=C2=A0=C2=A0 if (per_cpu(kvm_gpc_reader, cpu) =3D=3D gpc) > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cpumask_set_cpu(cpu, gpc_rea= ders); > > __kvm_kick_many_cpus(cpus, wait); >=20 >=20 > I'm literally sitting here watching you reinvent what SRCU already does. The problem, for me at least, is that SRCU does this and a _lot_ more. > Which, again, is *fine* given the behaviour of *these* read-side sections= . Well, yeah. Why use a nailgun to put a nail into the wall to hang a pictur= e frame? (other than the indisputable fact that power tools are fun). SRCU i= s fantastic infrastructure, but I genuinely think it's not the right fit here= , especially since we'll likely need a different solution for in-guest reader= s anyways. > I get it. RCU is a versatile tool, and in *some* cases the *Sleepable* > variant of RCU gets used in ways which would cause grace period latencies > which are thoroughly unacceptable in an MMU notifier callback. >=20 > But in the specific case of a dedicated kvm->gpc_srcu whose only > readers are tiny snippets of code that until today were always run with > rwlock_irqsave? That is *not* Jason's worst-case bugbear. It's fine. I agree it's more than likely fine for your use case, I'm not convinced it'= ll be fine for use cases that heavily overcommit memory, or do NUMA balancing, or= (close your eyes) enable KSM. E.g. it doesn't take all that much for even a single expedited sync to gene= rate a delay of 20ms. https://lore.kernel.org/all/20260309193059.2244645-1-seanjc@google.com