[tedesco]

This answer might be a little late, but it still might be usefull to some one:

I also noticed a excessive memory usage specially when the VSX has been logging locally for a while.

The solution is to switch the logs on the VSX/VS. (it it not the same than to switch on the CMA/MDS.)

You can check the size of your file by loging on the vsx and doing:
[Expert@vsxxxx]# cd /var/opt/CPfw1-V25/CTX/
[Expert@vsxxxx]# du -sk */log | sort -n
...
3708 CTX00074/log
3724 CTX00072/log
3760 CTX00096/log
...

Then you can list the local logs:
[Expert@vsxxxx]# vrfctl -s 96
[Expert@vsxxxx]# fw -vs 96 lslogs
Size Log file name
2152KB 2005-11-04_142611.log
1529KB fw.log

Finally you can switch the logs, using the command line or the Smartview tracker for the corresponding cma/VS. (Tools/Remote Files Management)