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Re: [Xen-devel] copy on write memory

On Tue, 2004-11-16 at 12:09 -0600, Adam Heath wrote:
> On Mon, 15 Nov 2004, Rik van Riel wrote:
> > On Mon, 15 Nov 2004, Peri Hankey wrote:
> >
> > > It occurred to me that the equivalent in the Xen world would be to use
> > > one Linux xenU domain purely as a page-table manager for a collection of
> > > separate xenU domains that are expected or known have similar process
> > > populations.
> >
> > UML copy on write is only for filesystems, isn't it ?
> And, since UML can use mmap access, if there are shared filesystems, it can
> reduce memory pressure.  Maybe that is something that can be worked on for
> xen.

If you're going to design a system like this I believe it's important to
also consider a method of re-sharing filesystems.  With UML after a
length of time all the software will not be shared anymore and you see
no memory gains.  There really needs to be a way for things to be re-
linked.  VServer does this on a filesystem level by doing a name,
permissions, and SHA1 hash comparision.  I think for a CoW file-backed
disk image you'd have to do block level though.  This way if httpd
binary get updated (ie. via yum/apt/up2date) on all domains that have a
shared backing store there should be a method to re-share that httpd

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