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

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Message-ID: <20190206185233.GE12227@ziepe.ca>
Date:   Wed, 6 Feb 2019 11:52:33 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Doug Ledford <dledford@...hat.com>, 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, Feb 06, 2019 at 10:35:04AM -0800, Matthew Wilcox wrote:

> > Admittedly, I'm coming in late to this conversation, but did I miss the
> > portion where that alternative was ruled out?
> 
> That's my preferred option too, but the preponderance of opinion leans
> towards "We can't give people a way to make files un-truncatable".

I haven't heard an explanation why blocking ftruncate is worse than
giving people a way to break RDMA using process by calling ftruncate??

Isn't it exactly the same argument the other way?

Jason