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

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Message-ID: <01000168bf23d0fa-f96456c7-8569-4542-9926-f91baa3c0f06-000000@email.amazonses.com>
Date:   Tue, 5 Feb 2019 19:30:22 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Ira Weiny <ira.weiny@...el.com>
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>,
        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

On Mon, 4 Feb 2019, Ira Weiny 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.
> >
> > Can we just disable RDMA to regular filesystems? Regular filesystems
> > should have full control of the write back and dirty status of their
> > pages.
>
> That may be a solution to the corruption/crashes but it is not a solution which
> users want to see.  RDMA directly to file systems (specifically DAX) is a use
> case we have seen customers ask for.

DAX is a special file system that does not use writeback for the DAX
mappings. Thus it could be an exception. And the pages are already pinned.