1.\" Copyright (c) 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)mlock.2 8.2 (Berkeley) 12/11/93 29.\" $FreeBSD: src/lib/libc/sys/mlock.2,v 1.6.2.5 2001/12/14 18:34:01 ru Exp $ 30.\" $DragonFly: src/lib/libc/sys/mlock.2,v 1.4 2006/02/17 19:35:06 swildner Exp $ 31.\" 32.Dd May 18, 2004 33.Dt MLOCK 2 34.Os 35.Sh NAME 36.Nm mlock , 37.Nm munlock 38.Nd lock (unlock) physical pages in memory 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/mman.h 44.Ft int 45.Fn mlock "const void *addr" "size_t len" 46.Ft int 47.Fn munlock "const void *addr" "size_t len" 48.Sh DESCRIPTION 49The 50.Fn mlock 51system call 52locks into memory the physical pages associated with the virtual address 53range starting at 54.Fa addr 55for 56.Fa len 57bytes. 58The 59.Fn munlock 60call unlocks pages previously locked by one or more 61.Fn mlock 62calls. 63For both, the 64.Fa addr 65parameter should be aligned to a multiple of the page size. 66If the 67.Fa len 68parameter is not a multiple of the page size, it will be rounded up 69to be so. 70The entire range must be allocated. 71.Pp 72After an 73.Fn mlock 74call, the indicated pages will cause neither a non-resident page 75nor address-translation fault until they are unlocked. 76They may still cause protection-violation faults or TLB-miss faults on 77architectures with software-managed TLBs. 78The physical pages remain in memory until all locked mappings for the pages 79are removed. 80Multiple processes may have the same physical pages locked via their own 81virtual address mappings. 82A single process may likewise have pages multiply-locked via different virtual 83mappings of the same pages or via nested 84.Fn mlock 85calls on the same address range. 86Unlocking is performed explicitly by 87.Fn munlock 88or implicitly by a call to 89.Fn munmap 90which deallocates the unmapped address range. 91Locked mappings are not inherited by the child process after a 92.Xr fork 2 . 93.Pp 94Since physical memory is a potentially scarce resource, processes are 95limited in how much they can lock down. 96A single process can 97.Fn mlock 98the minimum of 99a system-wide ``wired pages'' limit and 100the per-process 101.Li RLIMIT_MEMLOCK 102resource limit. 103.Pp 104These calls are only available to the super-user. 105.Sh RETURN VALUES 106.Rv -std 107.Pp 108If the call succeeds, all pages in the range become locked (unlocked); 109otherwise the locked status of all pages in the range remains unchanged. 110.Sh ERRORS 111.Fn Mlock 112will fail if: 113.Bl -tag -width Er 114.It Bq Er EPERM 115The caller is not the super-user. 116.It Bq Er EINVAL 117The address given is not page aligned or the length is negative. 118.It Bq Er EAGAIN 119Locking the indicated range would exceed either the system or per-process 120limit for locked memory. 121.It Bq Er ENOMEM 122Some portion of the indicated address range is not allocated. 123There was an error faulting/mapping a page. 124.El 125.Fn Munlock 126will fail if: 127.Bl -tag -width Er 128.It Bq Er EPERM 129The caller is not the super-user. 130.It Bq Er EINVAL 131The address given is not page aligned or the length is negative. 132.It Bq Er ENOMEM 133Some portion of the indicated address range is not allocated. 134Some portion of the indicated address range is not locked. 135.El 136.Sh "SEE ALSO" 137.Xr fork 2 , 138.Xr mincore 2 , 139.Xr minherit 2 , 140.Xr mmap 2 , 141.Xr munmap 2 , 142.Xr setrlimit 2 , 143.Xr getpagesize 3 144.Sh HISTORY 145The 146.Fn mlock 147and 148.Fn munlock 149functions first appeared in 150.Bx 4.4 . 151.Sh BUGS 152The per-process resource limit is a limit on the amount of virtual 153memory locked, while the system-wide limit is for the number of locked 154physical pages. 155Hence a process with two distinct locked mappings of the same physical page 156counts as 2 pages against the per-process limit and as only a single page 157in the system limit. 158.Pp 159The per-process resource limit is not currently supported. 160