RE: [Xen-devel] failed to start centos 5 domU with maxmem=30000

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> This is problem, because a'm using centos, debian, ubuntu, opensuse and
> other systems in domU, but i read that tmem support needed in dom0 and
> domU. Debian and Ubuntu i think, does not support this... But i'm try.

I have kernel rpm's for some versions of Oracle Enterprise Linux
that might work on the same version of centos.  I'm told that an
earlier version of the tmem patch (without self-ballooning) was
added to opensuse.

Due to upstream Linux kernel change requests, the tmem Linux patches
continue to change... cosmetic changes, all core functionality
is the same.  I've been focused on that rather than on keeping
the patches for older versions up to date.  But if you are eager
to try tmem on a particular distro and you have experience in
patching kernels for that distro, I would be happy to help.

Also, tmem does not require dom0 kernel changes, but the toolset
that create domains must be aware of tmem because tmem introduces
the concept of "freeable" memory... since tmem eventually uses all
free memory in the system, creating a domain may require freeable
memory to be freed and the tools need to know how to do that.
Xend (xm) works fine as of 4.0.0.

Again, efficient utilization of memory is a very hard problem.
"Simple" solutions that have been tried to date (such as externally
ballooning all guests from the host, and page sharing with host
swapping) have unacceptable side-effects.  Tmem uses paravirtualization
to achieve a much more efficient solution to the problem, but it
requires guest changes.

Thanks,
Dan

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