linux-kernel - Re: [RFC PATCH v2 0/5] Reduce NUMA balance caused TLB-shootdowns in a VM

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Message-ID: <ZN2qg4cPC2hEgtmY@yzhao56-desk.sh.intel.com>
Date:   Thu, 17 Aug 2023 13:05:07 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     John Hubbard <jhubbard@...dia.com>
CC:     David Hildenbrand <david@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <pbonzini@...hat.com>, <seanjc@...gle.com>,
        <mike.kravetz@...cle.com>, <apopple@...dia.com>, <jgg@...dia.com>,
        <rppt@...nel.org>, <akpm@...ux-foundation.org>,
        <kevin.tian@...el.com>, Mel Gorman <mgorman@...hsingularity.net>,
        <alex.williamson@...hat.com>
Subject: Re: [RFC PATCH v2 0/5] Reduce NUMA balance caused TLB-shootdowns in
 a VM

On Wed, Aug 16, 2023 at 11:00:36AM -0700, John Hubbard wrote:
> On 8/16/23 02:49, David Hildenbrand wrote:
> > But do 32bit architectures even care about NUMA hinting? If not, just
> > ignore them ...
> 
> Probably not!
> 
> ...
> > > So, do you mean that let kernel provide a per-VMA allow/disallow
> > > mechanism, and
> > > it's up to the user space to choose between per-VMA and complex way or
> > > global and simpler way?
> > 
> > QEMU could do either way. The question would be if a per-vma settings
> > makes sense for NUMA hinting.
> 
> From our experience with compute on GPUs, a per-mm setting would suffice.
> No need to go all the way to VMA granularity.
> 
After an offline internal discussion, we think a per-mm setting is also
enough for device passthrough in VMs.

BTW, if we want a per-VMA flag, compared to VM_NO_NUMA_BALANCING, do you
think it's of any value to providing a flag like VM_MAYDMA?
Auto NUMA balancing or other components can decide how to use it by
themselves.