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Browse Prior Art Database

An Efficient and Fair Memory Aging Scheme

IP.com Disclosure Number: IPCOM000120441D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 40K

Publishing Venue

IBM

Related People

Rasmussen, EG: AUTHOR

Abstract

Described is a technique for use in a computer operating system which combines the efficiency of interrupt-time aging and the fairness of task time aging without the overhead of an ager thread.

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This is the abbreviated version, containing approximately 93% of the total text.

An Efficient and Fair Memory Aging Scheme

      Described is a technique for use in a computer operating system
which combines the efficiency of interrupt-time aging and the
fairness of task time aging without the overhead of an ager thread.

      In the prior art three of the known aging schemes are explained
as follows:
1.   Age segments at interrupt time.  At periodic intervals, scan
some of the segments belonging to the current process.  If a segment
has been accessed since the last scan, mark recently used.
2.   Age segments at task time.  When a thread gives up the CPU, scan
some of the segments belonging to its process.  Mark the accessed
segments as recently used. This is fair, but is far too time
consuming to be practical.  The aging takes place too frequently.
3.   Create a separate ager thread.  This thread would enumerate all
segments belonging to all processes and would run only as frequently
as need be.  This is fair and not impractical, but incurs the use of
an additional thread.

      In the technique of this disclosure age segments at task time,
but only at periodic intervals.  This is a hybrid of schemes 1 and 2
above.  For each process, keep track of the time it was last aged.
When a thread gives up the CPU, check the timestamp of the owning
process.  If its segments have not been aged within the aging
interval, age them.  If the process has been aged recently, do not
age it.

      This combines the regularity of scheme...