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Combined Real/Virtual Fixed-Size Buffer Mechanism in Shared Storage

IP.com Disclosure Number: IPCOM000043820D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 6 page(s) / 56K

Publishing Venue

IBM

Related People

Bolton, DW: AUTHOR [+3]

Abstract

The technique to be described provides a combined real/virtual storage mechanism from a common storage pool where a virtual buffer facility uses under-utilized real storage. It can be used with microprocessors with multiple priority interrupt levels where a machine check/program check activates the highest priority interrupt level and where there is no hardware protection to main storage.

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Combined Real/Virtual Fixed-Size Buffer Mechanism in Shared Storage

The technique to be described provides a combined real/virtual storage mechanism from a common storage pool where a virtual buffer facility uses under-utilized real storage. It can be used with microprocessors with multiple priority interrupt levels where a machine check/program check activates the highest priority interrupt level and where there is no hardware protection to main storage. The control program/operating system of the microprocessor employs machine check/program check error processing on the highest priority interrupt level, an interrupt handler to control level interrupts, device communication on next highest interrupt levels, a control program scheduler and services on next priority interrupt level, and multiple tasking application programs executing basic processor instructions on remaining processor interrupt levels. Volatile control storage is used for system control tables, resident control programs, and as a storage pool into which transient control programs are scatter loaded. Storage is reserved for overlay pages of the control program. Another storage pool provides real fixed size storage blocks to requesting tasks for use as task control blocks, program work areas, and for I/O buffers. Storage allocation for application tasks is a control program service which records allocated storage by task within control tables and available storage within chain entries in a Block Allocation Table (BAT). A system control value is used which defines the maximum number of storage blocks in the storage pool. There is a maximum potential storage demand value for a task which requires to be satisfied before that task can be executed. A task can be rolled out to the direct access storage device (DASD) as it is waiting but not ready for execution at a roll point and another task is ready for execution. A task is executed only if its maximum potential storage demand from roll point to roll point can be made available from the system storage blocks currently available. Tasks often underuse the maximum potential demand made available to the task, when the task is actually being executed. The problem is the ability to satisfy a request for buffer allocation of a buffer combination that is larger than the maximum potential storage demand. It is not possible to increase the maximum potential storage demand because of the limiting effect on the number of concurrent executing tasks. It is then necessary to provide a virtual buffer mechanism in addition to a real buffer mechanism. Frequently there will not be enough storage for an independent virtual buffer mechanism. Existing storage management systems frequently operate at all times with a significant reserve of storage which is unused but which, because of storage management rules, will not be allocated. In the modified storage management subsystem described below, this idle storage is used to implement a cache of ...