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[174.3.196.123]) by smtp.gmail.com with ESMTPSA id m67sm19284132pfb.25.2019.02.11.14.12.48 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 11 Feb 2019 14:12:48 -0800 (PST) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1gtJol-0003Sa-Rp; Mon, 11 Feb 2019 15:12:47 -0700 Date: Mon, 11 Feb 2019 15:12:47 -0700 From: Jason Gunthorpe To: John Hubbard Cc: Ira Weiny , Dan Williams , Jan Kara , Dave Chinner , Christopher Lameter , Doug Ledford , Matthew Wilcox , lsf-pc@lists.linux-foundation.org, linux-rdma , Linux MM , Linux Kernel Mailing List , Jerome Glisse , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190211221247.GI24692@ziepe.ca> References: <01000168c8e2de6b-9ab820ed-38ad-469c-b210-60fcff8ea81c-000000@email.amazonses.com> <20190208044302.GA20493@dastard> <20190208111028.GD6353@quack2.suse.cz> <20190211102402.GF19029@quack2.suse.cz> <20190211180654.GB24692@ziepe.ca> <20190211181921.GA5526@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 11, 2019 at 01:22:11PM -0800, John Hubbard wrote: > The only way that breaks is if longterm pins imply an irreversible action, such > as blocking and waiting in a way that you can't back out of or get interrupted > out of. And the design doesn't seem to be going in that direction, right? RDMA, vfio, etc will always have 'long term' pins that are irreversible on demand. It is part of the HW capability. I think the flag is badly named, it is really more of a GUP_LOCK_PHYSICAL_ADDRESSES flag. 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. Short term GUP doesn't need that kind of lock. Jason