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.\"	$NetBSD: madvise.2,v 1.7 1995/12/27 21:17:02 jtc Exp $
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.\"	@(#)madvise.2	8.1 (Berkeley) 6/9/93
.\"
.Dd June 9, 1993
.Dt MADVISE 2
.Os
.Sh NAME
.Nm madvise ,
.Nm posix_madvise
.Nd give advice about use of memory
.Sh SYNOPSIS
.Fd #include <sys/mman.h>
.Ft int
.Fo madvise
.Fa "void *addr"
.Fa "size_t len"
.Fa "int advice"
.Fc
.Ft int
.Fo posix_madvise
.Fa "void *addr"
.Fa "size_t len"
.Fa "int advice"
.Fc
.Sh DESCRIPTION
The
.Fn madvise
system call allows a process that has knowledge of its memory behavior
to describe it to the system.
The advice passed in may be used by the system
to alter its virtual memory paging strategy.
This advice may improve application and system performance.
The behavior specified in
.Fa advice
can only be one of the following values:
.Pp
.Bl -tag -width MADV_SEQUENTIAL
.It Dv  MADV_NORMAL
Indicates that the application has no advice to give on its behavior
in the specified address range.
This is the system default behavior.
This is used with 
.Fn madvise
system call.
.It Dv POSIX_MADV_NORMAL
Same as MADV_NORMAL but used with 
.Fn posix_madvise
system call.
.It Dv MADV_SEQUENTIAL
Indicates that the application expects to access this address range
in a sequential manner.
This is used with
.Fn madvise
system call.
.It Dv POSIX_MADV_SEQUENTIAL
Same as MADV_SEQUENTIAL but used with 
.Fn posix_madvise
system call.
.It Dv MADV_RANDOM
Indicates that the application expects to access this address range
in a random manner.
This is used with
.Fn madvise
system call.
.It Dv POSIX_MADV_RANDOM
Same as MADV_RANDOM but used with 
.Fn posix_madvise
system call.
.It Dv MADV_WILLNEED
Indicates that the application expects to access this address range soon.
This is used with
.Fn madvise
system call.
.It Dv POSIX_MADV_WILLNEED
Same as MADV_WILLNEED but used with 
.Fn posix_madvise
system call.
.It Dv MADV_DONTNEED
Indicates that the application is not expecting
to access this address range soon.
This is used with
.Fn madvise
system call.
.It Dv POSIX_MADV_DONTNEED
Same as MADV_DONTNEED but used with 
.Fn posix_madvise
system call.
.It Dv MADV_FREE
Indicates that the application will not need the information contained
in this address range, so the pages may be reused right away.
The address range will remain valid.
This is used with
.Fn madvise
system call.
.El
.Pp
The
.Fn posix_madvise
behaves same as 
.Fn madvise
except that it uses values with POSIX_ prefix for the 
.Fa advice
system call argument.
.Sh RETURN VALUES
Upon successful completion,
a value of 0 is returned.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn madvise
fails if one or more of the following are true:
.Bl -tag -width Er
.\" ==========
.It Bq Er EINVAL
The value of 
.Fa advice 
is incorrect.
.\" ==========
.It Bq Er EINVAL
The address range includes unallocated regions.
.\" ==========
.It Bq Er ENOMEM
The virtual address range specified by the 
.Fa addr
and
.Fa len
are outside the range allowed for the address space.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Pp
.Ft int
.br
.Fo madvise
.Fa "caddr_t addr"
.Fa "size_t len"
.Fa "int advice"
.Fc ;
.Pp
.Ft int
.br
.Fo posix_madvise
.Fa "caddr_t addr"
.Fa "size_t len"
.Fa "int advice"
.Fc ;
.Pp
The include file
.In sys/types.h
is necessary.
The type of
.Fa addr
has changed.
.Sh SEE ALSO
.Xr mincore 2 ,
.Xr minherit 2 ,
.Xr mprotect 2 , 
.Xr msync 2 ,
.Xr munmap 2 ,
.Xr compat 5
.Sh HISTORY
The
.Nm madvise
function first appeared in 4.4BSD.
The
.Nm posix_madvise
function is part of IEEE 1003.1-2001
and was first implemented in Mac OS X 10.2.