5 Storage Management in Common Lisp

5.4 Controlling memory expansion

Lisp automatically expands memory as needed during the execution of a program. You can control memory expansion either by changing the parameters that control automatic memory expansion or by explicitly expanding the dynamic areas and the reserved area.

In general, you should use the default parameters and monitor the progress of garbage collections and memory expansion. If garbage collections occur often or if the dynamic or reserved areas are expanded too frequently, you can increase the size of these areas to reduce the number of garbage collections.

If your application requires a specific amount of memory and you are concerned about efficient memory use, you can adjust the memory management parameters to accommodate the application. To adjust the parameters, you must know how much memory the application uses. Ephemeral garbage collection normally reduces the amount of dynamic space needed by your application, so if you have already adjusted an application for use with just dynamic garbage collection, you should reevaluate the application's storage needs when using ephemeral garbage collection. You can use the following general guidelines to determine an application's memory needs:

Begin with relatively small dynamic areas and use the default ephemeral levels.
Set a high growth limit to allow your application enough room to expand memory.
Run the application, then use theroom function to report how much memory the application uses.
If your application is spending too much time either garbage collecting objects or expanding the reserved and dynamic areas, you can reduce the number of initial garbage collections by explicitly expanding the reserved and dynamic areas when the image is started.

The functionchange-memory-management allows you to change the parameters that control memory expansion and to explicitly expand the dynamic and reserved areas.

5.4.1 - Changing memory expansion parameters
5.4.2 - Explicitly expanding memory

The User's Guide - 9 SEP 1996

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