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

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Message-ID: <20190204233513.GA7917@iweiny-DESK2.sc.intel.com>
Date:   Mon, 4 Feb 2019 15:35:14 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Christopher Lameter <cl@...ux.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, 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.

I think this is the correct path toward supporting this use case.

Ira