1.\" $OpenBSD: madvise.2,v 1.23 2024/01/21 17:46:03 deraadt Exp $ 2.\" $NetBSD: madvise.2,v 1.7 1995/12/27 21:17:02 jtc Exp $ 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93 32.\" 33.Dd $Mdocdate: January 21 2024 $ 34.Dt MADVISE 2 35.Os 36.Sh NAME 37.Nm madvise , 38.Nm posix_madvise 39.Nd give advice about use of memory 40.Sh SYNOPSIS 41.In sys/mman.h 42.Ft int 43.Fn madvise "void *addr" "size_t len" "int behav" 44.Ft int 45.Fn posix_madvise "void *addr" "size_t len" "int behav" 46.Sh DESCRIPTION 47The 48.Fn madvise 49system call 50allows a process that has knowledge of its memory behavior 51to describe it to the system. 52The 53.Fn posix_madvise 54interface has the same effect, but returns the error value 55instead of only setting 56.Va errno . 57.Pp 58The possible behaviors are: 59.Bl -tag -width MADV_SEQUENTIAL 60.It Dv MADV_NORMAL 61No further special treatment needed. 62.It Dv MADV_RANDOM 63Expect random page access patterns. 64.It Dv MADV_SEQUENTIAL 65Expect sequential page references. 66.It Dv MADV_WILLNEED 67The pages will be referenced soon. 68.It Dv MADV_DONTNEED 69The pages will not be referenced soon. 70.It Dv MADV_SPACEAVAIL 71Ensure that resources are reserved. 72.It Dv MADV_FREE 73The pages don't contain any useful data and can be recycled. 74.El 75.Pp 76Portable programs that call the 77.Fn posix_madvise 78interface should use the aliases 79.Dv POSIX_MADV_NORMAL , POSIX_MADV_RANDOM , 80.Dv POSIX_MADV_SEQUENTIAL , POSIX_MADV_WILLNEED , 81and 82.Dv POSIX_MADV_DONTNEED 83rather than the flags described above. 84.Sh RETURN VALUES 85.Rv -std madvise 86.Pp 87If successful, the 88.Fn posix_madvise 89function will return zero. 90Otherwise an error number will be returned to indicate the error. 91.Sh ERRORS 92.Fn madvise 93will fail if: 94.Bl -tag -width Er 95.It Bq Er EINVAL 96The specified 97.Fa behav 98argument was invalid. 99.It Bq Er EINVAL 100The 101.Fa addr 102parameter was not page aligned or 103.Fa addr 104and 105.Fa size 106specify a region that would extend beyond the end of the address space. 107.It Bq Er EPERM 108The 109.Fa addr 110and 111.Fa len 112parameters specify a region which contains at least one page marked immutable. 113.El 114.Sh SEE ALSO 115.Xr mimmutable 2 , 116.Xr minherit 2 , 117.Xr mprotect 2 , 118.Xr msync 2 , 119.Xr munmap 2 120.Sh STANDARDS 121The 122.Fn posix_madvise 123system call conforms to 124.St -p1003.1-2008 . 125.Pp 126The 127.Er EPERM 128failure conditions described are an extension to this specification. 129.Sh HISTORY 130The 131.Fn madvise 132function first appeared in SunOS 4.0 and has been available since 133.Ox 2.7 . 134The 135.Fn posix_madvise 136function first appeared in 137.Ox 4.8 . 138.Sh BUGS 139The 140.Dv MADV_WILLNEED 141behavior is ignored. 142The 143.Dv MADV_SPACEAVAIL 144behavior is not implemented and will always fail. 145