From: Sean Christopherson <seanjc@google.com>
To: James Houghton <jthoughton@google.com>
Cc: David Matlack <dmatlack@google.com>, Peter Xu <peterx@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Axel Rasmussen <axelrasmussen@google.com>,
Linux MM <linux-mm@kvack.org>, kvm <kvm@vger.kernel.org>,
chao.p.peng@linux.intel.com, Oliver Upton <oupton@google.com>
Subject: Re: [RFC] Improving userfaultfd scalability for live migration
Date: Wed, 4 Jan 2023 00:57:09 +0000 [thread overview]
Message-ID: <Y7TO5Xxi5RWw1Xa6@google.com> (raw)
In-Reply-To: <CADrL8HV2K=NAGATdRobq8aMJJwRapiF7gxrJovhz7k-Me3ZFuw@mail.gmail.com>
On Thu, Dec 08, 2022, James Houghton wrote:
> - For the no-slow-GUP choice, if someone MADV_DONTNEEDed memory and we
> didn't know about it, we would get stuck in MADV_POPULATE_WRITE. By
> using UFFD_FEATURE_THREAD_ID, we can tell if we got a userfault for a
> thread that is in the middle of a MADV_POPULATE_WRITE, and we can try
> to unblock the thread by doing an extra UFFDIO_CONTINUE.
>
> - For the PF_NO_UFFD_WAIT choice, if someone MADV_DONTNEEDed memory,
> we would just keep trying to start the vCPU without doing anything (we
> assume some other thread has UFFDIO_CONTINUEd for us). This is
> basically the same as if we were stuck in MADV_POPULATE_WRITE, and we
> can try to unblock the thread in a fashion similar to how we would in
> the other case.
>
> So really these approaches have similar requirements for what
> userspace needs to track. So I think I prefer the no-slow-GUP approach
> then.
Are you planning on sending a patch (RFC?) for the no-slow-GUP approach? It sounds
like there's a rough consensus that that's a viable, minimally invasive solution.
next prev parent reply other threads:[~2023-01-04 0:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-01 19:37 [RFC] Improving userfaultfd scalability for live migration James Houghton
2022-12-03 1:03 ` Sean Christopherson
2022-12-05 15:27 ` Peter Xu
2022-12-05 17:31 ` David Matlack
2022-12-05 18:03 ` David Matlack
2022-12-05 18:23 ` Sean Christopherson
2022-12-05 18:20 ` Sean Christopherson
2022-12-05 21:19 ` James Houghton
2022-12-06 1:06 ` Sean Christopherson
2022-12-06 17:35 ` James Houghton
2022-12-06 18:00 ` Sean Christopherson
2022-12-06 20:41 ` James Houghton
2022-12-08 1:56 ` David Matlack
2022-12-08 17:50 ` James Houghton
2023-01-04 0:57 ` Sean Christopherson [this message]
2023-01-04 1:05 ` James Houghton
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