From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <478A03D8.9050308@qumranet.com> Date: Sun, 13 Jan 2008 14:28:08 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [kvm-devel] mmu notifiers References: <20080109181908.GS6958@v2.random> <47860512.3040607@qumranet.com> <47891A5C.8060907@qumranet.com> <20080113120939.GA3221@sgi.com> In-Reply-To: <20080113120939.GA3221@sgi.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Robin Holt Cc: Christoph Lameter , Andrea Arcangeli , kvm-devel@lists.sourceforge.net, linux-mm@kvack.org, Daniel J Blueman List-ID: Robin Holt wrote: > On Sat, Jan 12, 2008 at 09:51:56PM +0200, Avi Kivity wrote: > >> Christoph Lameter wrote: >> >>> On Thu, 10 Jan 2008, Avi Kivity wrote: >>> >>> >>> >>>> Actually sharing memory is possible even without this patch; one simply >>>> mmap()s a file into the address space of both guests. Or are you >>>> referring to >>>> something else? >>>> >>>> >>> A file from where? If a file is read by two guests then they will have >>> distinct page structs. >>> >>> >>> >> Two kvm instances mmap() the file (from anywhere) into the guest address >> space. That memory is shared, and will be backed by the same page structs >> at the same offset. >> > > That sounds nice, but... > > For larger machine configurations, we have different memory access > capabilities. When a partition that is located close to the home node > of the memory accesses memory, it is normal access. When it is further > away, they get special access to the line. Before the shared line is > sent to the reading node, it is converted by the memory controller into > an exclusive request and the reading node is handed the only copy of > the line. If we gave a remote kernel access to the page, we would also > open the entire owning nodes page tables up to speculative references > which effectively would be viewed by hardware as cache-line contention. > > Additionally, we have needs beyond memory backed by files. Including > special devices which do not have struct pages at all (see mspec.c). > I don't understand. I was just explaining how kvm shares memory among guests (which does not require mmu notifiers); if you have some other configuration that can benefit from mmu notifiers, then, well, great. -- error compiling committee.c: too many arguments to function -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org