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

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Message-ID: <4271b91c-90b7-4b48-b761-b4535b2ae9b7@nvidia.com>
Date:   Mon, 14 Aug 2023 19:34:09 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Yan Zhao <yan.y.zhao@...el.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>
Subject: Re: [RFC PATCH v2 0/5] Reduce NUMA balance caused TLB-shootdowns in a
 VM

On 8/14/23 02:09, Yan Zhao wrote:
...
>> hmm_range_fault()-based memory management in particular might benefit
>> from having NUMA balancing disabled entirely for the memremap_pages()
>> region, come to think of it. That seems relatively easy and clean at
>> first glance anyway.
>>
>> For other regions (allocated by the device driver), a per-VMA flag
>> seems about right: VM_NO_NUMA_BALANCING ?
>>
> Thanks a lot for those good suggestions!
> For VMs, when could a per-VMA flag be set?
> Might be hard in mmap() in QEMU because a VMA may not be used for DMA until
> after it's mapped into VFIO.
> Then, should VFIO set this flag on after it maps a range?
> Could this flag be unset after device hot-unplug?
> 

I'm hoping someone who thinks about VMs and VFIO often can chime in.


thanks,
-- 
John Hubbard
NVIDIA