Number of pages for memory mapping for HFS files (MAXMMAPAREA)

Specify the maximum amount of data space storage space (in pages) that can be allocated for memory mapping of HFS files. Storage is not allocated until the memory mapping is active.

Using memory map services causes a large amount of system memory to be consumed. For each page (4KB) that is memory-mapped, 96 bytes of Extended System Queue Area (ESQA) are consumed when a file is not shared with any other users. When a file is shared by multiple users, each user after the first causes 32 bytes of ESQA to be consumed for each shared page. Assuming that the default of 40960 pages is taken, and assuming that no sharing is done by mmap() users, a maximum of 384KB of ESQA could be consumed. The ESQA storage is consumed when the mmap() function is invoked rather than when the page is accessed by the memory mapping application program.

If you have applications using the __MAP_MEGA option, you can map very large files without the system overhead in ESQA.

Default: 40960

Range: 1 to 16777216.