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A Robust Method of Frame Allocation

IP.com Disclosure Number: IPCOM000012731D
Original Publication Date: 2003-May-22
Included in the Prior Art Database: 2003-May-22
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Abstract

The current frame allocation algorithm in z/OS* provides frames to all requestors when available frames exist, in all situations, regardless of the significance of the request. This method has allowed the pool of available frames to become depleted and subsequently cause system outages when no frames exist for non-suspendable requestors. In OS/390*, expanded storage provided a cache for auxiliary storage where real storage could be paged out to expanded quickly to replenish the system's supply of frames. Such a cache does not exist for z/OS*; thus a new frame management algorithm is required which will better maintain the system's supply of frames.

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A Robust Method of Frame Allocation

  Disclosed is a more robust method of frame (unit of real storage) allocation that preserves a set of frames for non-suspendable units of work. The invention involves two distinct software components: a Real Storage Manager (RSM) which has direct control over real storage and a System Resource Manager (SRM) which monitors real storage usage as well as other system resources periodically and directs RSM accordingly. We also divide frame requestors into two types: (1) critical - requestors who cannot suspend for a frame and (2) suspendable - requestors who could suspend for a frame. In the critical case (1) when there is no available frame of the desired type, the RSM invokes an algorithm referred to as Pref Steal. Pref Steal attempts to steal an in use frame of the desired type either by simply taking the frame when the frame is unchanged in real, or by exchanging the frame with a different available frame. In the event that an exchange frame is unavailable there is a high likelihood that the Pref Steal algorithm may fail which may potentially lead to the failure of a critical system function. In the suspendable case (2), the requestor suspends and is resumed when a frame of the desired type becomes available.

    In order to improve the likelihood of the availability of an exchange frame for the critical case, a new frame threshold is used. Whereas before this invention, RSM would allocate its last frame to a suspendable requestor, now it will allocate frames for suspendable requests until the count of available frames reaches a new threshold...