From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roland Dreier Subject: Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6 Date: Fri, 08 Feb 2008 16:12:42 -0800 Message-ID: References: <20080208220616.089936205@sgi.com> <20080208142315.7fe4b95e.akpm@linux-foundation.org> <20080208233636.GG26564@sgi.com> <20080208234302.GH26564@sgi.com> <20080208155641.2258ad2c.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: andrea@qumranet.com, a.p.zijlstra@chello.nl, izike@qumranet.com, steiner@sgi.com, linux-kernel@vger.kernel.org, avi@qumranet.com, linux-mm@kvack.org, daniel.blueman@quadrics.com, Robin Holt , general@lists.openfabrics.org, Andrew Morton , kvm-devel@lists.sourceforge.net To: Christoph Lameter Return-path: In-Reply-To: (Christoph Lameter's message of "Fri, 8 Feb 2008 16:05:00 -0800 (PST)") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: general-bounces@lists.openfabrics.org Errors-To: general-bounces@lists.openfabrics.org List-Id: kvm.vger.kernel.org > We have done several rounds of discussion on linux-kernel about this so > far and the IB folks have not shown up to join in. I have tried to make > this as general as possible. Sorry, this has been on my "things to look at" list for a while, but I haven't gotten a chance to really understand where things are yet. In general, this MMU notifier stuff will only be useful to a subset of InfiniBand/RDMA hardware. Some adapters are smart enough to handle changing the IO virtual -> bus/physical mapping on the fly, but some aren't. For the dumb adapters, I think the current ib_umem_get() is pretty close to as good as we can get: we have to keep the physical pages pinned for as long as the adapter is allowed to DMA into the memory region. For the smart adapters, we just need a chance to change the adapter's page table when the kernel/CPU's mapping changes, and naively, this stuff looks like it would work. Andrew, does that help? - R.