On 10/10/07, Avi Kivity <[EMAIL PROTECTED]> wrote: > Jun Koi wrote: > > On 10/10/07, Avi Kivity <[EMAIL PROTECTED]> wrote: > > > >> Jun Koi wrote: > >> > >>> Hi, > >>> > >>> On 10/10/07, Avi Kivity <[EMAIL PROTECTED]> wrote: > >>> > >>> > >>>> We've now switched to allocating guest memory in userspace rather than > >>>> in the kernel. This is important if you have a mainframe, but also if > >>>> you want to share memory between guests and implement nice features like > >>>> swapping. > >>>> > >>>> > >>> This is interesting! But how can we do that now? (share memory between > >>> guests) > >>> > >>> > >>> > >> It's not exposed by qemu, but you can now mmap() some file (or use SysV > >> shared memory) and use that as guest memory. > >> > >> > > > > OK, lets say we have 2 guest VMs share a memory, like mmap() a tmpfs > > file (which is actually in memory). Now one writes to the memory > > (shared file). Can we guarantee that the memory immediately updated, > > so other will see the change immediately? Or the data might be cached > > for a while, befere being flushed to the shared memory? > > > > Changes are visible immediately. >
OK, that is about sharing memory file. How about a shared file in which a file is a real physical file on the host? As far as I remember, there is a caution about sharing a file using mmap() between 2 processes, that is: if the first process modifies the shared file, it might take a while for the changes to be flushed from cache to the file. That means the other process doesnt see the change immediately. I guess this problem affects us in this case, when we use a real (physical) file to share between 2 VMs, correct? Thanks, Jun ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
