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Re: [Qemu-devel] [PATCH 14/23] userfaultfd: wake pending userfaults
From: |
Andrea Arcangeli |
Subject: |
Re: [Qemu-devel] [PATCH 14/23] userfaultfd: wake pending userfaults |
Date: |
Thu, 22 Oct 2015 17:30:55 +0200 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
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.