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[174.3.196.123]) by smtp.gmail.com with ESMTPSA id b26sm35017680pfe.91.2018.12.18.19.03.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 18 Dec 2018 19:03:30 -0800 (PST) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1gZS8v-0003uX-I6; Tue, 18 Dec 2018 20:03:29 -0700 Date: Tue, 18 Dec 2018 20:03:29 -0700 From: Jason Gunthorpe To: Dave Chinner Cc: Jan Kara , Jerome Glisse , John Hubbard , Matthew Wilcox , Dan Williams , John Hubbard , Andrew Morton , Linux MM , tom@talpey.com, Al Viro , benve@cisco.com, Christoph Hellwig , Christopher Lameter , "Dalessandro, Dennis" , Doug Ledford , Michal Hocko , mike.marciniszyn@intel.com, rcampbell@nvidia.com, Linux Kernel Mailing List , linux-fsdevel Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions Message-ID: <20181219030329.GI21992@ziepe.ca> References: <20181207191620.GD3293@redhat.com> <3c4d46c0-aced-f96f-1bf3-725d02f11b60@nvidia.com> <20181208022445.GA7024@redhat.com> <20181210102846.GC29289@quack2.suse.cz> <20181212150319.GA3432@redhat.com> <20181212214641.GB29416@dastard> <20181214154321.GF8896@quack2.suse.cz> <20181216215819.GC10644@dastard> <20181218103306.GC18032@quack2.suse.cz> <20181218234254.GC31274@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181218234254.GC31274@dastard> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 19, 2018 at 10:42:54AM +1100, Dave Chinner wrote: > Essentially, what we are talking about is how to handle broken > hardware. I say we should just brun it with napalm and thermite > (i.e. taint the kernel with "unsupportable hardware") and force > wait_for_stable_page() to trigger when there are GUP mappings if > the underlying storage doesn't already require it. If you want to ban O_DIRECT/etc from writing to file backed pages, then just do it. Otherwise I'm not sure demanding some unrealistic HW design is reasonable. ie nvme drives are not likely to add page faulting to their IO path any time soon. A SW architecture that relies on page faulting is just not going to support real world block IO devices. GPUs and one RDMA are about the only things that can do this today, and they are basically irrelevant to O_DIRECT. Jason