HI Offer, Unfortunately this is the way it works under z/Linux. Of course because of the way z/VM tries to Share memory once memory for a z/Linux guest is pushed into cache it is not considered when z/VM is trying to manage the memory by taking from one to give to another, it limits z/VM in its' memory management process. In Linux he sees having a bunch o f cache as a good thing because he has use of the cache and allows in most cases for better performance. So as you can see there is a conflict here. The hope is that these types of conflicts including double paging due to the same LRU approach used by both z/Linux and z/VM, as well as a way to dynamically prioritize the workloads for not only z/VM but for processes running in z/Linux can be resolved.
Anyway for now the best approach for the cache is to try to size the memory of the z/Linux guest to where you just see a very small amount of SWAPPING and make this SWAPPING go to VDISK. VDISK SWAPPING is a memory speed in z/VM so it is very fast. This will set the behavior so that z/Linux does not cache. I know from my own experiences that this is not always an easy thing to nail down but for the most part I have been able to balance this between the OSs'. Thank You, Terry Martin Lockheed Martin - Citic z/OS and z/VM Performance Tuning and Operating Systems Support Office - 443 348-2102 Cell - 443 632-4191 -----Original Message----- From: Linux on 390 Port [mailto:[email protected]] On Behalf Of Offer Baruch Sent: Thursday, February 11, 2010 8:18 AM To: [email protected] Subject: Linux file system cache Hi all, One of the problems with Linux under VM (not just z/VM I guess) is that no matter how much memory you allocate to the guest it will consume it all as cache. It just seems reasonable to be able to limit this cache to a user defined value leaving the rest of it for the applications. Sadly I couldn't find a parameter to enforce this limit. So, my question is, is there a way to limit the cache? If not, why? Obviously this caching method is just not good enough under VM. Decreasing and increasing memory for a guest is quite disruptive and adding 100M to an oracle guest just looks bad :-) Thanks! Offer Baruch No virus found in this outgoing message. Checked by AVG - www.avg.com Version: 9.0.733 / Virus Database: 271.1.1/2680 - Release Date: 02/10/10 21:38:00 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
