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.\"	@(#)madvise.2	8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: January 21 2024 $
.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 ERRORS
.Fn madvise
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The specified
.Fa behav
argument was invalid.
.It Bq Er EINVAL
The
.Fa addr
parameter was not page aligned or
.Fa addr
and
.Fa size
specify a region that would extend beyond the end of the address space.
.It Bq Er EPERM
The
.Fa addr
and
.Fa len
parameters specify a region which contains at least one page marked immutable.
.El
.Sh SEE ALSO
.Xr mimmutable 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 .
.Pp
The
.Er EPERM
failure conditions described are an extension to this specification.
.Sh HISTORY
The
.Fn madvise
function first appeared in SunOS 4.0 and has been available since
.Ox 2.7 .
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.