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

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Message-ID: <b8794103-5ae1-ff8d-22be-d585d36e6310@nvidia.com>
Date:   Tue, 12 Feb 2019 18:58:10 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Christopher Lameter <cl@...ux.com>
CC:     Jason Gunthorpe <jgg@...pe.ca>, Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        Doug Ledford <dledford@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        <lsf-pc@...ts.linux-foundation.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving
 longterm-GUP usage by RDMA

On 2/12/19 8:39 AM, Christopher Lameter wrote:
> On Mon, 11 Feb 2019, John Hubbard wrote:
> 
>> But anyway, Jan's proposal a bit earlier today [1] is finally sinking into
>> my head--if we actually go that way, and prevent the caller from setting up
>> a problematic gup pin in the first place, then that may make this point sort
>> of moot.
> 
> Ok well can be document how we think it would work somewhere? Long term
> mapping a page cache page could a problem and we need to explain that
> somewhere.
> 

Yes, once the dust settles, I think Documentation/vm/get_user_pages.rst is the
right place. I started to create that file, but someone observed that my initial
content was entirely backward-looking (described the original problem, instead 
of describing how the new system would work). So I'll use this opportunity for 
a do-over. :)

thanks,
-- 
John Hubbard
NVIDIA