1994-05-27 05:00:24 +00:00
|
|
|
.\" 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. All advertising materials mentioning features or use of this software
|
|
|
|
|
.\" must display the following acknowledgement:
|
|
|
|
|
.\" This product includes software developed by the University of
|
|
|
|
|
.\" California, Berkeley and its contributors.
|
|
|
|
|
.\" 4. 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
|
|
|
|
|
.\"
|
1996-07-20 04:37:26 +00:00
|
|
|
.Dd Jul 19, 1996
|
1994-05-27 05:00:24 +00:00
|
|
|
.Dt MADVISE 2
|
|
|
|
|
.Os
|
|
|
|
|
.Sh NAME
|
|
|
|
|
.Nm madvise
|
|
|
|
|
.Nd give advise about use of memory
|
|
|
|
|
.Sh SYNOPSIS
|
1996-02-02 05:06:29 +00:00
|
|
|
.Fd #include <sys/types.h>
|
|
|
|
|
.Fd #include <sys/mman.h>
|
1996-03-02 17:34:28 +00:00
|
|
|
.Fn madvise "caddr_t addr" "size_t len" "int behav"
|
1994-05-27 05:00:24 +00:00
|
|
|
.Sh DESCRIPTION
|
|
|
|
|
The
|
|
|
|
|
.Fn madvise
|
|
|
|
|
system call
|
|
|
|
|
allows a process that has knowledge of its memory behavior
|
|
|
|
|
to describe it to the system.
|
|
|
|
|
The known behaviors are given in
|
|
|
|
|
.Pa <sys/mman.h> :
|
|
|
|
|
.Bd -literal
|
1996-07-20 04:37:26 +00:00
|
|
|
#define MADV_NORMAL 0 /* no further special treatment */
|
|
|
|
|
#define MADV_RANDOM 1 /* expect random page references */
|
|
|
|
|
#define MADV_SEQUENTIAL 2 /* expect sequential references */
|
|
|
|
|
#define MADV_WILLNEED 3 /* will need these pages */
|
|
|
|
|
#define MADV_DONTNEED 4 /* don't need these pages */
|
|
|
|
|
#define MADV_FREE 5 /* data is now unimportant */
|
1994-05-27 05:00:24 +00:00
|
|
|
.Ed
|
1996-07-20 04:37:26 +00:00
|
|
|
.sp
|
|
|
|
|
MADV_NORMAL tells the system to revert to the default paging
|
|
|
|
|
behavior.
|
|
|
|
|
.sp
|
|
|
|
|
MADV_RANDOM is a hint that pages will be accessed randomly, and prefetching
|
|
|
|
|
is likely not advantageous.
|
|
|
|
|
.sp
|
|
|
|
|
MADV_SEQUENTIAL causes the VM system to depress the priority of
|
|
|
|
|
pages immediately preceeding a given page when it is faulted in.
|
|
|
|
|
.sp
|
|
|
|
|
MADV_WILLNEED causes pages that are in a given virtual address range
|
|
|
|
|
to temporarily have higher priority, and if they are in
|
|
|
|
|
memory, decrease the likelihood of them being freed. Additionally,
|
|
|
|
|
the pages that are already in memory will be immediately mapped into
|
|
|
|
|
the process, thereby eliminating unnecessary overhead of going through
|
|
|
|
|
the entire process of faulting the pages in. This WILL NOT fault
|
|
|
|
|
pages in from backing store, but quickly map the pages already in memory
|
|
|
|
|
into the calling process.
|
|
|
|
|
.sp
|
|
|
|
|
MADV_DONTNEED allows the VM system to decrease the in-memory priority
|
|
|
|
|
of pages in the specified range. Additionally future references to
|
|
|
|
|
this address range will incur a page fault.
|
|
|
|
|
.sp
|
|
|
|
|
MADV_FREE gives the VM system the freedom to free pages,
|
|
|
|
|
and and tells the system that information in the specified page range
|
|
|
|
|
is no longer important. This is an efficient way of allowing malloc(3) to
|
|
|
|
|
free pages anywhere in the address space, while keeping the address space
|
|
|
|
|
valid. The next time that the page is referenced, the page might be demand
|
|
|
|
|
zeroed, or might contain the data that was there before the MADV_FREE call.
|
|
|
|
|
References made to that address space range will not make the VM system
|
|
|
|
|
page the information back in from backing store until the page is
|
|
|
|
|
modified again.
|
|
|
|
|
|
1994-05-27 05:00:24 +00:00
|
|
|
.Sh SEE ALSO
|
|
|
|
|
.Xr msync 2 ,
|
|
|
|
|
.Xr munmap 2 ,
|
|
|
|
|
.Xr mprotect 2 ,
|
1996-01-23 23:33:55 +00:00
|
|
|
.Xr mincore 2 .
|
|
|
|
|
|
1994-05-27 05:00:24 +00:00
|
|
|
.Sh HISTORY
|
|
|
|
|
The
|
|
|
|
|
.Nm madvise
|
|
|
|
|
function first appeared in 4.4BSD.
|
