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

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Date:   Mon, 4 Sep 2023 17:18:39 +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 Thu, Aug 17, 2023 at 07:29:12PM -0700, John Hubbard wrote:
> On 8/17/23 17:13, Yan Zhao wrote:
> ...
> > But consider for GPUs case as what John mentioned, since the memory is
> > not even pinned, maybe they still need flag VM_NO_NUMA_BALANCING ?
> > For VMs, we hint VM_NO_NUMA_BALANCING for passthrough devices supporting
> > IO page fault (so no need to pin), and VM_MAYLONGTERMDMA to avoid misplace
> > and migration.
> > 
> > Is that good?
> > Or do you think just a per-mm flag like MMF_NO_NUMA is good enough for
> > now?
> > 
> 
> So far, a per-mm setting seems like it would suffice. However, it is
> also true that new hardware is getting really creative and large, to
> the point that it's not inconceivable that a process might actually
> want to let NUMA balancing run in part of its mm, but turn it off
> to allow fault-able device access to another part of the mm.
> 
> We aren't seeing that yet, but on the other hand, that may be
> simply because there is no practical way to set that up and see
> how well it works.
> 
>
Hi guys,
Thanks a lot for your review and suggestions!
I'll firstly try to add a per-mm flag to fix this problem later
(but maybe not very soon)

Thanks
Yan