VM65475: DEMAND SCAN RECLAIMS MORE STORAGE THAN NECESSARY

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When the system is short on memory, Demand Scan first tries to
  satisfy the need for frames from the reclaimable section of the
  Global Aging List.  After which, whether the need was satisfied
  or not, Demand Scan invokes HCPLANRS to free all of the storage
  in the VSwitch Global NDMBK recycle queue, and HCPKCLFW to free
  all available ISFC work units. This results in demand scan
  over-shooting the system need target, and a reduction in the
  efficiency achieved by maintaining the NDMBK recycle queue and
  the ISFC available work units queue.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of VSwitch or ISFC.                *
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  * PROBLEM DESCRIPTION:                                         *
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  * RECOMMENDATION: APPLY PTF                                    *
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  During a demand scan, HCPALDSC invokes HCPALGTA to reclaim
  frames from the Global Aging List to replenish the Global
  Available Lists.  If there are not enough reclaimable frames
  on the Global Aging List to satisfy the system need, HCPALGTA
  sets a non-zero frame manager deficit (RSAAGDFC) equal to the
  number of frames needed minus the number of frames reclaimed.
  Upon return to HCPALDSC, there is no check to determine whether
  RSAAGDFC is non-zero before invoking HCPKCLFW (to release all
  of the available LWKBKs, including the associated control pages
  and CCW pages), and stacking a call to HCPLANRS (to release the
  global NDMBK recycle queue).  With this behavior, any efficiency
  gained by ISFC and VSwitch in having these available pools of
  storage is lost once memory becomes over-committed, even in the
  case where demand scan is keeping up with the system's need for
  frames.
  

Problem conclusion

• HCPALDSC has been modified to call HCPKCLFW and stack a call to
  HCPLANRS only when the system's need for frames cannot be
  satisfied from the reclaimable section of the Global Aging List.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UM34269

Modules/Macros

• HCPALD
  

Fix information

• Fixed component name

  VM CP

• Fixed component ID

  568411202

Applicable component levels

• R630 PSY UM34269

     UP14/03/13 P 1501

Fix is available

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