[linux-mm-cc] First experience of compressed cache

[Nitin Gupta]

On Mon, Mar 31, 2008 at 3:37 PM,  <nai.xia at gmail.com> wrote:
> Hi, I found this project both from kernelnewbies.org and linux.org. I think it's
>  interesting and so I checked out the code HEAD and tried today.

I often leave SVN in uncompilable state or some half-cooked/untested
code which can cause strange bugs.
So, I would suggest you to use released version.

>  My first experience is based on a very simple RAM memory overloading:
>
>  1. Concurrently booted up two virutal machines which ate up about 75% of my total
>  virutal memory(RAM + hard-disk swap) without compcache.
>  2. Booted them with default loaded compcache (that means 25% of RAM was used as ramswap).
>
>  I saw a significant performance loss in the 2nd case. ( Actuall I killed one of
>  the virutal machines before it could eat all my hard-disk swap).
>
>  Does problem lie in the current "static cache" implementation?
>  Or was I just using it at the wrong place or with wrong module parameters?
>

I seems you are running compcache on host only and not inside VMs.
Try running compcache inside VMs (assuming these are Linux too). This
way you can run VMs with less
than usual RAM assigned. I am not very sure if running compcache on
host in addition to in VMs will have
any negative performance impact.


>  I get from the paper "Adaptive Compressed Caching: Design and Implementation"
>  that this method should suit to both hard swap backed cache and file cache,
>  while it seems that the features are still not in your code.
>
>  will all that features planned on the roadmap of the version based on kernel
>  2.6? (sorry, I did not find roadmap info in the project homepage)
>

Compressing page-cache(filesystem backed) pages, is highly desirable
but I don't yet have
a way of cleanly implementing this without intrusive kernel patching.
If you want an implementation for pagecache+swapcache compression, you
can refer patches
for 2.6.x at:

http://linuxcompressed.sourceforge.net/


>  I am very much interested in this project, however I am still a kernel newbie.
>  I will be very glad to help, if someone could kindly be my mentor. :-)
>  (And I am currently reading related papers and code by myself.)
>
>
>

I would be glad to help you out :)


Cheers,
Nitin