Subject: Re: [v3,2/3] powerpc/mm: Don't send IPI to all cpus on THP updates

From: Michael Ellerman <[email-masked]>
Date: Mon, 21 Aug 2017 23:39:09 +1000 (AEST)

On Thu, 2017-07-27 at 06:24:54 UTC, "Aneesh Kumar K.V" wrote:
> Now that we made sure that lockless walk of linux page table is mostly limitted
> to current task(current->mm->pgdir) we can update the THP update sequence to
> only send IPI to cpus on which this task has run. This helps in reducing the IPI
> overload on systems with large number of CPUs.
> 
> W.r.t kvm even though kvm is walking page table with vpc->arch.pgdir, it is
> done only on secondary cpus and in that case we have primary cpu added to
> task's mm cpumask. Sending an IPI to primary will force the secondary to do
> a vm exit and hence this mm cpumask usage is safe here.
> 
> W.r.t CAPI, we still end up walking linux page table with capi context MM. For
> now the pte lookup serialization sends an IPI to all cpus in CPI is in use. We
> can further improve this by adding the CAPI interrupt handling cpu to task
> mm cpumask. That will be done in a later patch.
> 
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/fa4531f753f1c80d21b5eb86ec5c02

cheers