linux-kernel - Re: [PATCH v2 2/5] userfaultfd: non-cooperative: add event for memory unmaps

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Date:   Wed, 1 Feb 2017 08:37:48 +0200
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] userfaultfd: non-cooperative: add event for
 memory unmaps

On Tue, Jan 31, 2017 at 04:39:28PM -0800, Andrew Morton wrote:
> On Fri, 27 Jan 2017 20:44:30 +0200 Mike Rapoport <rppt@...ux.vnet.ibm.com> wrote:
> 
> > When a non-cooperative userfaultfd monitor copies pages in the background,
> > it may encounter regions that were already unmapped. Addition of
> > UFFD_EVENT_UNMAP allows the uffd monitor to track precisely changes in the
> > virtual memory layout.
> > 
> > Since there might be different uffd contexts for the affected VMAs, we
> > first should create a temporary representation for the unmap event for each
> > uffd context and then notify them one by one to the appropriate userfault
> > file descriptors.
> > 
> > The event notification occurs after the mmap_sem has been released.
> 
> I was going to bug you about not updating
> Documentation/vm/userfaultfd.txt but the UFFD_FEATURE flags aren't
> documented?
 
I'm going to send the documentation update in the next few days.

--
Sincerely yours,
Mike.