linux-kernel - Re: [RFC PATCH 3/3] KVM: x86/mmu: skip zap maybe-dma-pinned pages for NUMA migration

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Date:   Wed, 9 Aug 2023 08:59:16 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     Sean Christopherson <seanjc@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, mike.kravetz@...cle.com, apopple@...dia.com,
        rppt@...nel.org, akpm@...ux-foundation.org, kevin.tian@...el.com
Subject: Re: [RFC PATCH 3/3] KVM: x86/mmu: skip zap maybe-dma-pinned pages
 for NUMA migration

On Wed, Aug 09, 2023 at 08:11:17AM +0800, Yan Zhao wrote:

> > Can we just tell userspace to mbind() the pinned region to explicitly exclude the
> > VMA(s) from NUMA balancing?

> For VMs with VFIO mdev mediated devices, the VMAs to be pinned are
> dynamic, I think it's hard to mbind() in advance.

It is hard to view the mediated devices path as a performance path
that deserves this kind of intervention :\

Jason