4.1cBSD/usr/man/man2/madvise.2

.TH MADVISE 2 2/12/83
.SH NAME
madvise \- give advice to the paging system
.SH SYNOPSIS
.nf
.ft B
#include <mman.h>
#include <sys/types.h>
.PP
.ft B
madvise(addr, len, behavior)
caddr_t addr; int len, behavior;
.fi
.SH DESCRIPTION
\fBThis 4.2 call is not implemented in 4.1c.\fP
.PP
.I Madvise
is used to inform the system that process paging
behavior merits special consideration.  The call
specifies that memory starting at
.I addr
and continuing for
.I len
bytes will exhibit a particular
.IR behavior .
The system may use this information to alter its
paging policy as best suits this behavior, though
nothing is guaranteed.
.TP 5
MADV_RANDOM
advises that the paging behavior is not likely to
be well handled by the system's default algorithm,
since reference information collected over macroscopic
intervals (e.g. 10-20 seconds) will not serve to indicate
future page references.  The system in this case will
choose to replace pages with little emphasis placed
on recent usage, and more emphasis on referenceless
circular behavior.  It is 
.I essential
that processes which have very random paging behavior
(such as LISP during garbage collection of very large
address spaces) call
.I madvise,
as otherwise the system has great difficulty dealing
with their page-consumptive demands.
.TP 5
MADV_NORMAL
restores default paging replacement behavior.
.TP 5
MADV_SEQUENTIAL
indicates sequential access should be expected
in the area of memory indicated.  The system should try
and prepage
.I forward
of the current reference, where possible.
.TP 5
MADVISE_WILLNEED
advises the system that the memory
indicated will be needed in the future and the associated pages
should not be, if possible, reclaimed.
.TP 5
MADVISE_WONTNEED
tells the system that the process has
no further need for the memory indicated and the associated
pages may be immediately reclaimed.
.SH "RETURN VALUE"
???
.SH ERRORS
???
.SH "SEE ALSO"
mmap(2), mincore(2), mremap(2), munmap(2)