Re: [ANNOUNCE] kvm-46 release

Avi Kivity
2007-10-10T09:07:44Z

Jun Koi wrote:
> On 10/10/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
>
>> Jun Koi wrote:
>>
>>> Hi,
>>>
>>> On 10/10/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> 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.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.