From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: Re: [PATCH] mmu notifiers #v5 Date: Fri, 1 Feb 2008 00:41:01 +0100 Message-ID: <20080131234101.GS7185@v2.random> References: <20080131045750.855008281@sgi.com> <20080131171806.GN7185@v2.random> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, steiner-sJ/iWh9BUns@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Avi Kivity , kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, daniel.blueman-xqY44rlHlBpWk0Htik3J/w@public.gmane.org, Robin Holt To: Christoph Lameter Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Thu, Jan 31, 2008 at 03:09:55PM -0800, Christoph Lameter wrote: > On Thu, 31 Jan 2008, Christoph Lameter wrote: > > > > pagefault against the main linux page fault, given we already have all > > > needed serialization out of the PT lock. XPMEM is forced to do that > > > > pt lock cannot serialize with invalidate_range since it is split. A range > > requires locking for a series of ptes not only individual ones. > > Hmmm.. May be okay after all. I see that you are only doing it on the pte > level. This means the range callbacks are taking down a max of 512 > entries. So you have a callback for each pmd. A callback for 2M of memory? Exactly. The point of _pages is to reduce of an order of magnitude (512, or 1024 times) the number of needed invalidate_page calls in a few places where it's a strightforward optimization for both KVM and GRU. Thanks to the PT lock this remains a totally obviously safe design and it requires zero additional locking anywhere (nor linux VM, nor in the mmu notifier methods, nor in the KVM/GRU page fault). Sure you can do invalidate_range_start/end for more than 2M(/4M on 32bit) max virtual ranges. But my approach that averages the fixed mmu_lock cost already over 512(/1024) ptes will make any larger "range" improvement not strongly measurable anymore given to do that you have to add locking as well and _surely_ decrease the GRU scalability with tons of threads and tons of cpus potentially making GRU a lot slower _especially_ on your numa systems. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/