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

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Message-ID: <01000168b980e880-a7d8e0db-84fb-4398-8269-149c66b701b4-000000@email.amazonses.com>
Date:   Mon, 4 Feb 2019 17:14:19 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     john.hubbard@...il.com
cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Christoph Hellwig <hch@...radead.org>,
        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

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.

Can we just disable RDMA to regular filesystems? Regular filesystems
should have full control of the write back and dirty status of their
pages.

Special filesystems that do not actually do write back (like hugetlbfs),
mmaped raw device files and anonymous allocations are fine.