Re: [PATCH 14/23] userfaultfd: wake pending userfaults

From	Andrea Arcangeli <aarcange@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 14/23] userfaultfd: wake pending userfaults
Date	2015-10-22 17:40 +0200
Message-ID	<qmq8a-6GG-3@gated-at.bofh.it> (permalink)
References	(2 earlier) <qmn0D-28d-27@gated-at.bofh.it> <qmo6n-3GO-15@gated-at.bofh.it> <qmog1-3Ro-1@gated-at.bofh.it> <qmoSJ-4U2-7@gated-at.bofh.it> <qmpOO-6iz-27@gated-at.bofh.it>
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On Thu, Oct 22, 2015 at 05:15:09PM +0200, Peter Zijlstra wrote:
> Indefinitely is such a long time, we should try and finish
> computation before the computer dies etc. :-)

Indefinitely as read_seqcount_retry, eventually it makes progress.

Even returning 0 from the page fault can trigger it again
indefinitely, so VM_FAULT_RETRY isn't fundamentally different from
returning 0 and retrying the page fault again later. So it's not clear
why VM_FAULT_RETRY can only try once more.

FAULT_FLAG_TRIED as a message to the VM so it starts to do heavy
locking and block more aggressively is actually useful as such, but it
shouldn't be a replacement of FAULT_FLAG_ALLOW_RETRY. What I meant
with removing FAULT_FLAG_TRIED is really about converting it to an
hint, but not controlling if the page fault can keep retrying
in-kernel.
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Re: [PATCH 14/23] userfaultfd: wake pending userfaults Peter Zijlstra <peterz@infradead.org> - 2015-10-22 14:20 +0200
  Re: [PATCH 14/23] userfaultfd: wake pending userfaults Andrea Arcangeli <aarcange@redhat.com> - 2015-10-22 15:30 +0200
    Re: [PATCH 14/23] userfaultfd: wake pending userfaults Peter Zijlstra <peterz@infradead.org> - 2015-10-22 15:40 +0200
      Re: [PATCH 14/23] userfaultfd: wake pending userfaults Andrea Arcangeli <aarcange@redhat.com> - 2015-10-22 16:20 +0200
        Re: [PATCH 14/23] userfaultfd: wake pending userfaults Peter Zijlstra <peterz@infradead.org> - 2015-10-22 17:20 +0200
          Re: [PATCH 14/23] userfaultfd: wake pending userfaults Andrea Arcangeli <aarcange@redhat.com> - 2015-10-22 17:40 +0200

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