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.\" $OpenBSD: madvise.2,v 1.19 2014/07/10 13:42:53 guenther Exp $
.\" $NetBSD: madvise.2,v 1.7 1995/12/27 21:17:02 jtc Exp $
.\"
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: July 10 2014 $
.Dt MADVISE 2
.Os
.Sh NAME
.Nm madvise ,
.Nm posix_madvise
.Nd give advice about use of memory
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn madvise "void *addr" "size_t len" "int behav"
.Ft int
.Fn posix_madvise "void *addr" "size_t len" "int behav"
.Sh DESCRIPTION
The
.Fn madvise
system call
allows a process that has knowledge of its memory behavior
to describe it to the system.
The
.Fn posix_madvise
interface has the same effect, but returns the error value
instead of only setting
.Va errno .
.Pp
The possible behaviors are:
.Bl -tag -width MADV_SEQUENTIAL
.It Dv MADV_NORMAL
No further special treatment needed.
.It Dv MADV_RANDOM
Expect random page access patterns.
.It Dv MADV_SEQUENTIAL
Expect sequential page references.
.It Dv MADV_WILLNEED
The pages will be referenced soon.
.It Dv MADV_DONTNEED
The pages will not be referenced soon.
.It Dv MADV_SPACEAVAIL
Ensure that resources are reserved.
.It Dv MADV_FREE
The pages don't contain any useful data and can be recycled.
.El
.Pp
Portable programs that call the
.Fn posix_madvise
interface should use the aliases
.Dv POSIX_MADV_NORMAL , POSIX_MADV_RANDOM ,
.Dv POSIX_MADV_SEQUENTIAL , POSIX_MADV_WILLNEED ,
and
.Dv POSIX_MADV_DONTNEED
rather than the flags described above.
.Sh RETURN VALUES
.Rv -std madvise
.Pp
If successful, the
.Fn posix_madvise
function will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh SEE ALSO
.Xr mincore 2 ,
.Xr minherit 2 ,
.Xr mprotect 2 ,
.Xr msync 2 ,
.Xr munmap 2
.Sh STANDARDS
The
.Fn posix_madvise
system call conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn madvise
function first appeared in
.Bx 4.4 .
The
.Fn posix_madvise
function first appeared in
.Ox 4.8 .
.Sh BUGS
The
.Dv MADV_WILLNEED
behavior is ignored.
The
.Dv MADV_SPACEAVAIL
behavior is not implemented and will always fail.
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