4. EXCEPTIONS › 4.3 Detailed Exception Descriptions › 02901: PLPA Packing Loss Exceeds Max

02901: PLPA Packing Loss Exceeds Max

FILE: Virtual Storage System Usage File
SAS FILE NAME: DAYS.SCPVSM01
SOURCE LOCATION: prefix.MICS.USER.SOURCE(DYRMFEXC)

SEVERITY: Impacting            (SEVERITY='I')
MANAGEMENT AREA: Performance   (MGMTAREA='PERFORMANCE')

PURPOSE:  Identify excessive virtual storage use within the
Pageable Link Pack Area (PLPA) caused by the use of the pack
list option.

RATIONALE:  PLPA paging can be reduced by forcing modules
that tend to be used together to be loaded into the same
page, or group of pages, in PLPA storage, thus reducing the
probability of additional pages being read from auxiliary
storage after the initial module is accessed.  When a group
of modules in the pack list is loaded into memory, any unused
space in the last page is never used.  This is in contrast to
normal PLPA loading, where an effort is made to make best use
of all space.  An excessive amount of space being wasted, as
a result of incomplete pages built during pack list
processing, may be cause for concern in virtual storage
constrained systems, especially if the amount is sufficient
to cause the LPA to exceed a one-megabyte segment boundary,
thereby making the private area one megabyte smaller than
necessary.

DEFINITION:  This exception is detected when the amount of
empty space caused by pack list processing exceeds an
installation-specified maximum.

EXCEPTION STATEMENTS:  The SAS statements identifying the
exception situation and describing the condition are stored
in the source member named in SOURCE LOCATION and are
described below:

/* ***************************************
**  02901 PLPA PACKING LOSS EXCEEDS MAX **
*************************************** */
IF VSMAPAKL GT kbyte
 THEN DO;
  EXCCODE='02901'; SEVERITY='I'; MGMTAREA='PERFORMANCE';
  EXCDESC1='PLPA PACKING LOSS EXCEEDS MAX';
  EXCDESC2='LOSS=' !! PUT(VSMAPAKL,4.) !! ' KBYTES';
  LINK HIT;
END;
THRESHOLD MODIFICATION:  The user should modify the kbyte
value according to the following convention:

kbyte - The maximum amount of unused space caused by pack
list processing.   A threshold 100 KB would appear as:

VSMAPAKL GT 100