Re: copy on write memory

[Kip Macy <kmacy@eventdriven.org>]

It doesn't sound like the performance benefit would justify the added
management complexity for xen.

				-Kip

On Thu, 18 Nov 2004, Keir Fraser wrote:

> > >
> > > Is there any documentation on the semantics of DCSS and the hypervisor
> > > services that are used? It would be interesting to see if Xen ought to
> > > have some similar concept.
> >
> > This doesn't really answer your question - but the closest your likely
> > to get is at their pubs:
> >
> > http://www.vm.ibm.com/pubs/
>
> There's a manual called "How to Improve the Performance of Linux on
> z/VM with Execute-In-Place Technology", which is easily googled for.
> Turns out that DCSSs are pretty simple things -- just a blob of
> physmem that is mapped into phys address space of every Linux
> instance, and contains a read-only filesystem image. xip2fs is a
> simple read-only fs that serves mmap() requests directly out of the
> shared DCSS rather than the private block cache. Looks tedious to
> manage because the whole filesystem takes up space in every Linux
> memory map all the time, no matter whether a particular file/block is
> being used. So you have to be careful to put only frequently accessed
> and highly shared files in the filesystem and use twisted symlinks to
> link in from their usual location into the mounted xip2fs filesystem.
>
>  -- Keir
>
>
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