IBR

IBR Analysis

Specifics - IBR analysis:

IBR stands for Invalid but Resident. It is part of the new storage concept that replaces XSTORE (expanded storage) for handling memory activity as of z/VM 6.3. It contains several frame/page lists.
When the system needs real storage (memory), the algorithm selects frames/pages from the user and system owned lists. These pages are put in IBR state. Any access to a page in IBR state by guests results in revalidation. Otherwise, the frame associated with an IBR page is added to the global aging list to be reused.
Linux servers tend to do polling which causes the server to look at data then go back to sleep. If the few pages it touches at each dispatch get paged out (moved to DASD), the system page rate goes up. A high page rate will cause system performance impacts. (See Storage Level for more details.)
However the following can be done to improve IBR performance:
Set the size to 5%, earlywrites to yes and keepslot to yes. SET AGELIST SIZE 5% EARLYWRITES YES KEEPSLOT YES.

ESAUSTR - User Storage Utilization - Shows virtual and resident storage/paging rates activity. Both screen and report samples:

IBR - This shows Invalid But Resident pages above and below the 2GB line. Watch for significant changes.

AgeList - This shows the IBR storage in the agelist. The agelist is used by the system's frame replenishment algorithm when storage is needed. Watch for significant changes.

PreWrite IBR/Agelst - This shows pages either already backed on disk (IBR) or pages already written to disk (Agelst). If there are high numbers in these lists, it would indicate a problem.

The following settings are suggested by Velocity Software:

Use Q AGELIST to view the current settings.
Update Target size to 5.0% - SET AGELIST SIZE 5.0% - if needed. This gives a bigger buffer area.
Update Early writes to yes - SET AGELIST EARLYW YES - if needed. This allows unused pages to be written out early.
Update Keep slot to yes - SET AGELIST KEEPS YES - if needed. This keeps the storage address longer.