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Date:   Mon, 4 Feb 2019 11:09:34 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Christopher Lameter <cl@linux.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, john.hubbard@gmail.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
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        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH 0/6] RFC v2: mm: gup/dma tracking
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On Mon, Feb 04, 2019 at 06:21:39PM +0000, Christopher Lameter wrote:
> On Mon, 4 Feb 2019, Jason Gunthorpe wrote:
> 
> > On Mon, Feb 04, 2019 at 05:14:19PM +0000, Christopher Lameter wrote:
> > > Frankly I still think this does not solve anything.
> > >
> > > Concurrent write access from two sources to a single page is simply wrong.
> > > You cannot make this right by allowing long term RDMA pins in a filesystem
> > > and thus the filesystem can never update part of its files on disk.
> >
> > Fundamentally this patch series is fixing O_DIRECT to not crash the
> > kernel in extreme cases.. RDMA has the same problem, but it is much
> > easier to hit.
> 
> O_DIRECT is the same issue. O_DIRECT addresses always have been in
> anonymous memory or special file systems.

That's never been a constraint that's existed.