Mark Real Mode Region as Pageable

Call With

AX = 0602H
BX:CX = starting linear address of memory to mark as pageable
SI:DI = size of region to be marked (bytes)

Returns

if function successful
Carry flag = clear

if function unsuccessful
Carry flag = set
AX = error code

8002H	invalid state (region already marked as pageable)
8025H	invalid linear address (region is above 1 MB boundary)

Notes

• If the function returns an error, none of the memory has been marked as pageable.

• If the specified region overlaps part of a page at the beginning or end of the region, the page(s) will not be marked as pageable.

• Pageability information for a real mode region is maintained as a binary state, not a count. Therefore, multiple calls to this function for the same region have no effect.

• For compatibility with DPMI version 0.9 hosts, a client must call the Relock Real Mode Region function (Int 31H Function 0603H) to relock the memory region before terminating. Memory that remains unlocked after the client has terminated could result in fatal page faults when another program is executed in the same address space. DPMI 1.0 hosts automatically relock real mode memory at client termination.

• Under some DPMI hosts, all conventional memory may be locked by default. If a protected mode program is using memory in the first megabyte of address space, it is recommended that this function be used to turn off automatic page locking for regions of memory that will not be touched at interrupt time.

• The client must not mark memory as pageable in regions that it does not own; i.e. it may only mark as pageable memory that it has previously allocated with Int 31H Function 0100H or by a direct call to DOS via the translation functions. For example, marking all free DOS memory as pageable under some DPMI hosts could cause a page fault to occur while inside of DOS, resulting in a crash. Also, a client should not mark the DPMI host data area as pageable.

• Note that address space marked as pageable by this function can still be locked using the Lock Linear Region function (Int 31H Function 0600H). This function is just an advisory service to allow memory that does not need to be locked to be paged out; it disables any automatic locking of real mode memory performed by the DPMI host.

• This function is ignored by DPMI implementations that do not support virtual memory; the function will return the Carry flag clear to indicate success, but has no other effect. DPMI hosts which support virtual memory may also choose to ignore this function, but such hosts must be able to handle page faults transparently at arbitrary points during a client's execution, including within interrupt and exception handlers.