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  Copyright © 1997 Bryce Cogswell and Mark Russinovich

  Last Updated July 9, 1997

  Controlling the NT system cache

  Introduction  Windows NT provides system administrators with virtually
                no control over the system cache's sizing and write-back
                behaviors. Other than specifying that it should be Large
                or Small (the definitions of which are not documented by
                Microsoft), none of the cache's parameters can be
                altered. The Cache Manager uses a variety of complex
                equations to determine when it should grow and shrink,
                and when it should write dirty data back to disk. Use
                Cacheman to explore alternate NT system caching
                parameters to see if performance can be increased for
                particular applications (or in general!).

  Installation  To run Cacheman, simply copy the executable and driver to
       and Use  a local hard drive and type "cacheman". The Cacheman
                dialog dynamically loads the Cacheman driver. Cacheman
                presents Cache Manager tuning parameters as groups of
                related settings. Alter the settings you desire and then
                direct Cacheman to enforce your choices. Here is a brief
                description of each of the variables that Cacheman lets
                you change. While running Cacheman you can use the dialog
                help pointer to obtain these descriptions in a help
                balloon. Note that these are our best guesses as to what
                these variables represent and may not be totally
                accurate.

                   * CcFirstDelay Delay before writing back a page after
                     first access
                   * CcIdleDelay Idle period to wait before writing back
                     dirty pages
                   * CcCollisionDelay Delay by this amount if writeback
                     not possible
                   * CcTargetCleanDelay Standard delay before writing
                     back dirty data
                   * CcDirtyPageThreshold Maximum number of dirty pages
                     to allow in cache
                   * CcDirtyPageTarget Desired number of dirty pages in
                     cache
                   * CcAvailableMaxDirtyWrite Maximum number of dirty
                     pages to write back at a time
                   * CcAvailablePagesThreshold Require at least this many
                     pages available
                   * MmSystemCacheWsMinimum Minimum size of the working
                     set of the cache
                   * MmSystemCacheWsMaximum Maximum size of the working
                     set of the cache
                   * MmDoPeriodicAgressiveTrimming Agressively reduce
                     working sets of all tasks
                   * MmPeriodicAgressiveTrimMinFree Trim working set of
                     cache if available pages greater than this amount
                   * MmPeriodicAgressiveTrimMaxFree Trim working set of
                     cache if available pages less than this amount
                   * MmPeriodicAgressiveCacheWsMin Trim cache to this
                     amount periodically
                   * MmWorkingSetReductionMaxCacheWs Trim cache by this
                     amount if larger than max size
                   * MmWorkingSetVolReductionMaxCacheWs Trim cache by
                     this amount if larger than max size during volume
                     reduction

                Cacheman does not perform validity checking on input
                values so it is possible that entering inappropriate
                settings will result in the system becoming unstable or
                crashing. Changes to most of these variables will not
                immediately have a noticeable affect on the Cache's
                behavior or size unless the system is under heavy memory
                load. We have not spent much time experimenting with
                different values, so if you obtain benchmark performance
                results of the standard caching policy compared to one
                you have enabled, we would be interested in posting them.

                Cacheman runs on NT 4.0 Final Release, SP1, SP2 and SP3.

        Sample
    Screenshot  Here is a screenshot of Cacheman.

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