[frgeek-michiana] Compcache/ramzswap and LTSP
- From: Tony Germano <tony_germano@xxxxxxxxxxx>
- To: <frgeek-michiana@xxxxxxxxxxxxx>
- Date: Thu, 6 May 2010 16:42:17 -0400
I read an interesting article (http://lwn.net/Articles/334649/) about
compcache, a kernel module that creates a compressed swapfile in RAM. It has
some interesting use cases for both limited resource computing and
virtualization. While you decrease your main ram and incur some additional
overhead having to decompress the swap, it is orders of magnitude faster than
disk-based swap, effectively increasing your total ram for a very minimal
performance hit.
When running it in the hypervisor, you can increase the total amount of virtual
machines that a given server can host as the entire virtual machine runs in
swapable ram. There have been reports of performance boosts using compcache
when running a Windows VM under the KVM hypervisor.
More relevant to FGM is the increased amount of available ram to thin clients
without disk swap. The compcache developers did some performance testing with
LTSP running local firefox and kdpf. Here
(http://code.google.com/p/compcache/wiki/Performance/LTSPPerf) are the results.
They look promising. There is a dramatic increase in the amount of pdf files
that can be opened at once, as well as improvements in responsiveness when
paging through documents. Similar effects were seen in firefox when
switching/opening tabs.
Compcache is officially in the mainline kernel as of the most stable release
(2.6.33.3.) Ubuntu 10.04 is running 2.6.32, BUT they have patched their kernel
to add support (since version 8.10.) Note, they are not running the most recent
version of compcache. You can test it out by typing:
$ sudo modprobe ramzswap
$ sudo swapon /dev/ramzswap0 -p 100
The first line will load the module and create the default swap device 15% of
the size of physical ram. The second line activates the swap with higher
priority than default disk swap if it exists. The system will fall back to disk
swap if the ramzswap device is full.
Here (https://wiki.ubuntu.com/Compcache) is more information from the Ubuntu
wiki.
Tony
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