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Date:   Mon, 4 Feb 2019 16:59:17 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Christoph Hellwig <hch@infradead.org>
cc:     john.hubbard@gmail.com, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm@kvack.org, Al Viro <viro@zeniv.linux.org.uk>,
        Christian Benvenuti <benve@cisco.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Doug Ledford <dledford@redhat.com>, Jan Kara <jack@suse.cz>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jerome Glisse <jglisse@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Tom Talpey <tom@talpey.com>,
        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, 4 Feb 2019, Christoph Hellwig wrote:

> On Mon, Feb 04, 2019 at 04:08:02PM +0000, Christopher Lameter wrote:
> > It may be worth noting a couple of times in this text that this was
> > designed for anonymous memory and that such use is/was ok. We are talking
> > about a use case here using mmapped access with a regular filesystem that
> > was not initially intended. The mmapping of from the hugepages filesystem
> > is special in that it is not a device that is actually writing things
> > back.
> >
> > Any use with a filesystem that actually writes data back to a medium
> > is something that is broken.
>
> Saying it was not intended seems rather odd, as it was supported
> since day 0 and people made use of it.

Well until last year I never thought there was a problem because I
considered it separate from regular filesystem I/O.