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

[Avi Kivity <avi@redhat.com>]

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?

> o execute-in-place: This is a Linux feature to exploit the DCSS technology.
>   The goal is to shared identical guest pages without the additional overhead
>   of KSM etc. We have a block device driver for DCSS. This block device driver
>   supports the direct_access function and therefore allows to use the xip
>   option of ext2. The idea is to put  binaries into an read-only ext2
>   filesystem. Whenever an mmap is made on this file system, the page is not
>   mapped into the page cache. The ptes point into the DCSS memory instead.
>   Since the DCSS is demand-paged by the host no memory is wasted for unused
>   parts of the binaries. In case of COW the page is copied as usual. It turned
>   out that installations with many similar guests (lets say 400 guests) will
>   profit in terms of memory saving and quicker application startups (not the
>   first guest of course). There is a downside: this requires a skilled
>   administrator to setup.

ksm might be easier to admin, at the cost of some cpu time.

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