The maximum DMA transfer expressed in pages of memory. This amount must be less than the value of syssegsz and maxpmem.
Value
Default: 1024 pages
32-bit Range: 1 - syssegsz (maximum 0x20000)
64-bit Range: 1 - syssegsz (maximum 0x10000000)
When to Change
Change this parameter when you need to be able to use very large read or write system calls, or other system calls that perform large scale DMA. This situation typically arises when using optical scanners, film recorders or some printers.