Re: [PATCH v2] Driver for Inter-VM shared memory device for KVM supporting interrupts.

[Avi Kivity <avi@redhat.com>]

Christian Bornträger wrote:
> Am Mittwoch 20 Mai 2009 10:45:50 schrieb Avi Kivity:
>   
>> Christian Bornträger wrote:
>>     
>>> o shared guest kernels: The CMS operating system is build as a bootable
>>> DCSS (called named-saved-segments NSS). All guests have the same host
>>> pages for the read-only parts of the CMS kernel. The local data is stored
>>> in exclusive-write parts of the same NSS. Linux on System z is also
>>> capable of using this feature (CONFIG_SHARED_KERNEL). The kernel linkage
>>> is changed in a way to separate the read-only text segment from the other
>>> parts with segment size alignment
>>>       
>> How does patching (smp, kprobes/jprobes, markers/ftrace) work with this?
>>     
> It does not. :-) 
> Because of that and since most distro kernels are fully modular and kernel 
> updates are another problem this feature is not used very often for Linux. It 
> is used heavily in CMS, though.
> Actually, we could do COW in the host but then it is really not worth the 
> effort.
>   

ksm on low throttle would solve all of those problems.

> Yes, KSM is easier and it even finds duplicate data pages.
> On the other hand it does only provide memory saving. It does not speedup 
> application startup like execute-in-place (major page faults become minor page 
> faults for text pages if the page is already backed by the host)
> I am not claiming that KSM is useless. Depending on the scenario you might 
> want the one or the other or even both. For typical desktop use, KSM is very 
> likely the better approach

If ksm shares pagecache, then doesn't it become effectively XIP?

We could also hook virtio dma to preemptively share pages somehow.

-- 
error compiling committee.c: too many arguments to function