The fastscan default value is set in one of the following ways:
The fastscan value set in the /etc/system file is used.
The maxfastscan value set in the /etc/system file is used.
If neither fastscan nor maxfastscan is set in the /etc/system file, fastscan is set to 64 MB when the system is booted. Then, after the system is booted for a few minutes, the fastscan value is set to the number of pages that the scanner can scan in one second using 10% of a CPU.
In all three cases, if the derived value is more than half the memory in the system, the fastscan value is capped at the value of half the memory in the system.
64 MB to half the system's physical memory
Yes, unless dynamic reconfiguration operations that add or delete memory occur. At that point, the value is reset to the value provided by /etc/system or calculated from the new physical memory value.
The maximum value is the lesser of 64 MB and 1/2 of physical memory.
When more aggressive scanning of memory is preferred during periods of memory shortfall, especially when the system is subject to periods of intense memory demand or when performing heavy file I/O.