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

From: John Hubbard <jhubbard@nvidia.com>
To: Yan Zhao <yan.y.zhao@intel.com>
Cc: David Hildenbrand <david@redhat.com>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>,
	<pbonzini@redhat.com>, <seanjc@google.com>,
	<mike.kravetz@oracle.com>, <apopple@nvidia.com>, <jgg@nvidia.com>,
	<rppt@kernel.org>, <akpm@linux-foundation.org>,
	<kevin.tian@intel.com>, Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [RFC PATCH v2 0/5] Reduce NUMA balance caused TLB-shootdowns in a VM
Date: Mon, 14 Aug 2023 19:34:09 -0700	[thread overview]
Message-ID: <4271b91c-90b7-4b48-b761-b4535b2ae9b7@nvidia.com> (raw)
In-Reply-To: <ZNnvPuRUVsUl5umM@yzhao56-desk.sh.intel.com>

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