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Reducing Thrashing With Time-Outs

IP.com Disclosure Number: IPCOM000060055D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

McDermott, MJ: AUTHOR [+2]

Abstract

Thrashing is a common problem on systems with overcommitted storage. The more often virtual areas are moved in and out of storage, the worse system throughput becomes. Thrashing can be reduced by setting a timer after execution of a supervisor call (e.g., WAIT or CALL). The system storage manager is prevented from using the real storage associated with the related program until the timer expires. Statistics have shown that the longer a wait has been outstanding, the longer until the wait will be satisfied. Typically, systems have not differentiated between waits of various lengths when selecting virtual areas to remove from storage.

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Reducing Thrashing With Time-Outs

Thrashing is a common problem on systems with overcommitted storage. The more often virtual areas are moved in and out of storage, the worse system throughput becomes. Thrashing can be reduced by setting a timer after execution of a supervisor call (e.g., WAIT or CALL). The system storage manager is prevented from using the real storage associated with the related program until the timer expires. Statistics have shown that the longer a wait has been outstanding, the longer until the wait will be satisfied. Typically, systems have not differentiated between waits of various lengths when selecting virtual areas to remove from storage. The Region Time Out Counter (RTOC) processes wait lengths as follows: OE On known long waits, for example, workstation input wait or certain resource waits, RTOC immediately releases the storage of the virtual areas of the task's regions. Long waits can also be explicitly indicated. OE On unknown waits, RTOC does not release the storage of the virtual areas of the task's regions. Instead, RTOC assigns a specific time interval. If the time interval expires before the wait is satisfied, RTOC releases the virtual storage areas of the related program. Statistically, when the wait is not satisfied within the RTOC time interval, the time until the wait is satisfied is long. Thus RTOC reduces thrashing by increasing the probability of taking storage from virtual areas in long waits. RTOC is also used when on...