CAMASTER using high number of Real Storage frames

Products

• SYSVIEW Performance Management

Issue/Introduction

On one of the z/OS 2.4 images, CAMASTER is using a high number of Real Storage frames. 

This might have occurred right after varying a large number of devices online. 

But since this address space is 'non-cancellable, non-stoppable', how to get it to release that storage short of an IPL? 

Environment

SYSVIEW 16.0 & 17 - z/OS supported releases - 

 

Resolution

SYSVIEW does not delete its data spaces. They will remain there for the life of an IPL because they are used by several address spaces, including monitored CICS regions.

 

Wanting to keep device collection off then in SCHDMVS parmlib member do not comment out the entry for MVS-DEVICES. 

Leave it uncommented and make it DISABLED (rather than ENABLE).

Additional Information

For a given data space SYSVIEW allocates the entire 2G max up front (the Blocks field on DSLIST) and then does its own storage management within that 2G.  Even though 2G is allocated and available for use, data space storage isn't considered 'used' (the Useblk field) until you actually touch a block/page.  Touching a page causes it to be backed in a real frame, at least for some amount of time.

 

There isn't really a concept of freeing or releasing this data space storage - from the OS perspective all 2G is actually allocated and will never be freed.  It is a matter of how much of that 2G gets referenced thus causing it to reside in a real frame.  If the data in that real frame doesn't get touched again for some amount of time, then the OS can page that data out and reuse that real frame to back some other virtual storage page that someone else is referencing.  But that will only occur when a frame is needed and all other frames are currently being used.

 

So SYSVIEW is no longer actively touching all those 200k+ pages anymore, but they are still backed in real frames from earlier in the week when it was touching them all.  And those frames will continue to be assigned to this data space until the OS steals them to use for some other data.