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

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Message-ID: <01000168e29418ba-81301f56-9370-4555-b70c-3ad51be84543-000000@email.amazonses.com>
Date:   Tue, 12 Feb 2019 16:39:43 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     John Hubbard <jhubbard@...dia.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 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.

> > ie indicate to the FS that is should not attempt to remap physical
> > memory addresses backing this VMA. If the FS can't do that it must
> > fail.
> >
>
> Yes. Duration is probably less important than the fact that the page
> is specially treated.

Yup.