linux-kernel - Re: [PATCH 0/6] RFC v2: mm: gup/dma tracking

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Message-ID: <01000168b97322ff-7c681a52-566f-4de1-ba1e-0a045b7f3622-000000@email.amazonses.com>
Date:   Mon, 4 Feb 2019 16:59:17 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Christoph Hellwig <hch@...radead.org>
cc:     john.hubbard@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jerome Glisse <jglisse@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Tom Talpey <tom@...pey.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 0/6] RFC v2: mm: gup/dma tracking

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.