Re: memory hotplug for guests?

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Thursday 05 April 2007, Avi Kivity wrote:
> > arch/s390/mm/extmem.c has another very interesting concept, though the
> > hcall interfaces used there are not as flexible as they should be in
> > kvm. It's basically about mapping host files into the guest real address
> > space, e.g. for shared memory between guests.
> >   
> 
> This, too, is interesting, though it means guest apps need to be written 
> to take advantage of it.

The primary user of this interface is the ext2 file system with the -oxip
mount option that can easily share read-only file systems across guests
without actually copying files into the page cache of each guest.

Another potential (future) user are cluster file systems like ocfs2 and
gfs2, but to be really efficient, these also need a specialized distributed
lock manager that communicates through hcalls instead of TCP/IP networking.

Simply mapping the shared memory as a character device is similar enough
that applications written for posix shared memory can easily be adapted,
but I'm not aware of anyone doing that currently.

	Arnd <><

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