>>>>> On Tue, 13 Jul 1999 10:11:14 -0400 (EDT),
	"Brian F. Feldman" <green@FreeBSD.org> said:

>> > you also have to consider a program wishing to make sparse use
>> > of its address space, without overcommit it becomes impossible.
>> 
>> SVR4 has MAP_NORESERVE option for mmap(2) for this.
>> So, default behaivour don't have to be overcommitment.

> Isn't that just like mmap()ing then mlock()ing the range? That would
> keep it in core.

No.
MAP_NORESERVE is nothing related to page wiring (i.e. mlock()ing).

From Solaris 2.6 man page:
:      The MAP_NORESERVE option specifies that  no  swap  space  be
:      reserved  for a mapping.  Without this flag, the creation of
:      a writable MAP_PRIVATE mapping reserves swap space equal  to
:      the  size  of the mapping; when the mapping is written into,
:      the reserved space is employed to hold private copies of the
:      data.  A write into a MAP_NORESERVE mapping produces results
:      which depend on the current availability of  swap  space  in
:      the system.  If space is available, the write succeeds and a
:      private copy of the written page is created; if space is not
:      available, the write fails and a SIGBUS or SIGSEGV signal is
:      delivered to the writing process. MAP_NORESERVE mappings are
:      inherited  across  fork();  at  the time of the fork(), swap
:      space is reserved in the child for all  private  pages  that
:      currently  exist  in the parent; thereafter the child's map-
:      ping behaves as described above.
--
soda