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

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Message-ID: <01000168e2913f2e-56010847-a10b-407e-b4eb-7730164267de-000000@email.amazonses.com>
Date:   Tue, 12 Feb 2019 16:36:36 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Dan Williams <dan.j.williams@...el.com>
cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Matthew Wilcox <willy@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Dave Chinner <david@...morbit.com>,
        Doug Ledford <dledford@...hat.com>,
        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>,
        John Hubbard <jhubbard@...dia.com>,
        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, Dan Williams wrote:

> An mmap write after a fault due to a hole punch is free to trigger
> SIGBUS if the subsequent page allocation fails. So no, I don't see
> them as the same unless you're allowing for the holder of the MR to
> receive a re-fault failure.

Order 0 page allocation failures are generally not possible in that path.
System will reclaim and OOM before that happens.