linux-kernel - Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA

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Message-ID: <a5b976cad6a578f0a6e6573acbf547ceb9dad6c7.camel@redhat.com>
Date:   Wed, 06 Feb 2019 15:54:01 -0500
From:   Doug Ledford <dledford@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christopher Lameter <cl@...ux.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Jan Kara <jack@...e.cz>, Ira Weiny <ira.weiny@...el.com>,
        lsf-pc@...ts.linux-foundation.org, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        John Hubbard <jhubbard@...dia.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving
 longterm-GUP usage by RDMA

On Wed, 2019-02-06 at 12:20 -0800, Matthew Wilcox wrote:
> On Wed, Feb 06, 2019 at 03:16:02PM -0500, Doug Ledford wrote:
> > On Wed, 2019-02-06 at 11:40 -0800, Matthew Wilcox wrote:
> > > On Wed, Feb 06, 2019 at 07:16:21PM +0000, Christopher Lameter wrote:
> > > > though? If we only allow this use case then we may not have to worry about
> > > > long term GUP because DAX mapped files will stay in the physical location
> > > > regardless.
> > > 
> > > ... except for truncate.  And now that I think about it, there was a
> > > desire to support hot-unplug which also needed revoke.
> > 
> > We already support hot unplug of RDMA devices.  But it is extreme.  How
> > does hot unplug deal with a program running from the device (something
> > that would have returned ETXTBSY)?
> 
> Not hot-unplugging the RDMA device but hot-unplugging an NV-DIMM.

Is an NV-DIMM the only thing we use DAX on?


-- 
Doug Ledford <dledford@...hat.com>
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