AIX 5L Problem Determination - IBM Redbooks

► Shared subclass: This subclass receives all the memory pages used by
processes in more than one subclass of the superclass. This includes pages
in shared memory regions and pages in files that are used by processes in
more than one subclass of the same superclass. Shared memory and files
used by multiple processes that belong to a single subclass are associated
with that subclass. The pages are placed in the Shared subclass of the
superclass only when a process from a different subclass of the same
superclass accesses the shared memory region or file. There are no
processes in the Shared subclass. This subclass can only have physical
memory shares and limits applied to it. It cannot have shares or limits for the
other resource types or assignment rules specified.
Tiers
Tier configuration is based on the importance of a class relative to other classes
in WLM. There are 10 available tiers, from 0 through to 9. Tier value 0 is the most
important and value 9 is the least important. As a result, classes belonging to tier
0 will get resource allocation priority over classes in tier 1; classes in tier 1 will
have priority over classes in tier 2; and so on. The default tier number, if the
attribute is not specified, is 0.
The tier applies at both the superclass and subclass levels. Superclass tiers are
used to specify resource allocation priority between superclasses, and subclass
tiers are used to specify resource allocation priority between subclasses of the
same superclass. There is no relationship between tier numbers of subclasses of
different superclasses.
Tier separation, in terms of prioritization, is much more enforced in AIX 5L than in
the previous release. A process in tier 1 will never have priority over a process in
tier 0, since there is no overlapping of priorities in tiers. It is unlikely that classes
in tier 1 will acquire any resources if the processes in tier 0 are consuming all the
resources. This occurs because the control of leftover resources is much more
restricted than in the AIX Version 4.3.3 release of WLM, as shown in Figure 10-5
on page 281.
280 IBM ^ Certification Study Guide - AIX 5L Problem Determination Tools and Techniques