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[Xen-devel] Transcendent Memory ("tmem") -capable kernel now publicly released

Transcendent Memory ("tmem") [1] is a new approach to optimizing RAM utilization
in a virtualized (and, in some cases, a physical) environment

Support for tmem has been in the Xen hypervisor since the 4.0 release, but
the tmem protocols require cooperation between the hypervisor and guest
OS kernel.  While the guest-side kernel changes are relatively simple
and non-intrusive, getting any new technology into any operating system
can be, shall we say, challenging... :-)  BUT...

Last week, Oracle released "Oracle Unbreakable Enterprise Kernel Release 2",
the first publicly-available fully-supported[2] Linux kernel implementing all
Xen-guest-side capabilities for tmem, including "cleancache" (ephemeral tmem
pools), "frontswap" (persistent tmem pools), and in-kernel support for

So now, finally, it should be easy to give tmem a try!

Brief How-To:
1) Install [3] the UEK2 kernel (upgrade or co-existing) in your existing
   RHEL5 or RHEL6 (or Oracle Linux 5 or 6) PV or HVM guest(s).
2) Add the "tmem" kernel boot parameter in your guest's grub.conf.
3) Add the "tmem" Xen boot parameter on the xen.gz line in dom0's grub.conf.
   (Optionally add "tmem_compress" and "tmem_dedup" depending on your
    environment and testing plans.)
4) Reboot Xen and launch your guest(s).  Check to ensure the guests are
    running UEK2.
5) Start a workload on your guest(s).
6) Use xentop to watch the fun!  (Don't forget to press "t" in xentop for
   more detail.)

Dan Magenheimer

[1] For more information on tmem:

    Technical overview: http://oss.oracle.com/projects/tmem 
    Xen Summit 2010 (including performance analysis): 
    Tmem without virtualization: http://lwn.net/Articles/454795/ and 

[2] At this time, the tmem capability in UEK2 is officially a
    "Technology Preview" so is not recommended for production use.

[3] For more information on UEK2 including installation:

    UEK2 install/getting started: 

    UEK2 Release notes: 

    Press release: http://www.oracle.com/us/corporate/press/1555025 

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