Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents

Memory Pool System Project

                             VM MODULE ON DEC UNIX
                                design.mps.vmo1
                                 incomplete doc
                                 drj 1997-03-25

    INTRODUCTION

    .readership: Any MPS developer.

    .intro: This is the design of the VM Module for DEC UNIX (aka OSF/1 os.o1).  In
    general aspects (including interface) the design is as for design.mps.vm.

    DETAILS

    Functions

    .fun.unmap:

    VMUnmap

    It "unmaps" a region by replacing the existing mapping with a mapping using the
    vm->none_fd file descriptor (see mumble mumble, VMCreate), and protection set
    to PROT_NONE (ie no access).  .fun.unmap.justify: Replacing the mapping in this
    way means that the address space is still reserved and will not be used by
    calls to mmap (perhaps in other libraries) which specify MAP_VARIABLE.
    .fun.unmap.offset: The offset for this mapping is the offset of the region
    being unmapped in the VM; this gives the same effect as if there was one
    mapping of the vm->none_fd from the base to the limit of the VM (but "behind"
    all the other mappings that have been created).  .fun.unmap.offset.justify: If
    this is not done (if for example the offset is always specified as 0) then the
    VM will cause the kernel to create a new file reference for each mapping
    created with VMUnmap; eventually the kernel refuses the mmap call because it
    can't create a new file reference.

## A. References

## B. Document History

2002-06-07 | RB | Converted from MMInfo database design document.

## C. Copyright and License

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Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents