.\" $NetBSD: mlock.2,v 1.3 1995/06/24 10:42:03 cgd Exp $ .\" .\" Copyright (c) 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. .\" .\" @(#)mlock.2 8.2 (Berkeley) 12/11/93 .\" .Dd June 2, 1993 .Dt MLOCK 2 .Os .Sh NAME .Nm mlock , .Nm munlock .Nd lock (unlock) physical pages in memory .Sh SYNOPSIS .Fd #include <sys/mman.h> .Ft int .Fo mlock .Fa "const void *addr" .Fa "size_t len" .Fc .Ft int .Fo munlock .Fa "const void *addr" .Fa "size_t len" .Fc .Sh DESCRIPTION The .Nm mlock system call locks a set of physical pages into memory. The pages are associated with a virtual address range that starts at .Fa addr and extends for .Fa len bytes. The .Nm munlock call unlocks pages that were previously locked by one or more .Nm mlock calls. For both calls, the .Fa addr parameter should be aligned to a multiple of the page size. If the .Fa len parameter is not a multiple of the page size, it will be rounded up to be so. The entire range must be allocated. .Pp After an .Nm mlock call, the indicated pages will cause neither a non-resident page nor address-translation fault until they are unlocked. They may still cause protection-violation faults or TLB-miss faults on architectures with software-managed TLBs. The physical pages remain in memory until all locked mappings for the pages are removed. .Pp Multiple processes may have the same physical pages locked via their own virtual address mappings. Similarly, a single process may have pages multiply-locked via different virtual mappings of the same pages or via nested .Nm mlock calls on the same address range. Unlocking is performed explicitly by .Nm munlock or implicitly by a call to .Nm munmap , which deallocates the unmapped address range. Locked mappings are not inherited by the child process after a .Xr fork 2 . .Pp Because physical memory is a potentially scarce resource, processes are limited in how much memory they can lock down. A single process can .Nm mlock the minimum of a system-wide ``wired pages'' limit and the per-process .Li RLIMIT_MEMLOCK resource limit. .Sh RETURN VALUES A return value of 0 indicates that the call succeeded and all pages in the range have either been locked or unlocked, as requested. A return value of -1 indicates an error occurred and the locked status of all pages in the range remains unchanged. In this case, the global location .Va errno is set to indicate the error. .Sh ERRORS .Fn Mlock and .Fn munlock will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EINVAL The address given is not page-aligned or the length is negative. .\" =========== .It Bq Er ENOMEM Part or all of the specified address range is not mapped to the process. .El .Pp .Fn Mlock will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EAGAIN Locking the indicated range would exceed either the system or per-process limit for locked memory. .\" =========== .It Bq Er ENOMEM Some portion of the indicated address range is not allocated. There was an error faulting/mapping a page. .El .Pp .Fn Munlock will fail if: .Bl -tag -width Er .\" =========== .It Bq Er ENOMEM Some portion of the indicated address range is not allocated. Some portion of the indicated address range is not locked. .El .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/mman.h> .Pp The include file .In sys/types.h is necessary. .Pp .Ft int .br .Fo mlock .Fa "caddr_t addr" .Fa "size_t len" .Fc ; .Pp .Ft int .br .Fo munlock .Fa "caddr_t addr" .Fa "size_t len" .Fc ; .Pp The variable type of .Fa addr has changed. .Sh "SEE ALSO" .Xr fork 2 , .Xr mincore 2 , .Xr minherit 2 , .Xr mmap 2 , .Xr munmap 2 , .Xr setrlimit 2 , .Xr getpagesize 3 , .Xr compat 5 .Sh BUGS Unlike The Sun implementation, multiple .Nm mlock calls on the same address range require the corresponding number of .Nm munlock calls to actually unlock the pages, i.e. .Nm mlock nests. This should be considered a consequence of the implementation and not a feature. .Pp The per-process resource limit is a limit on the amount of virtual memory locked, while the system-wide limit is for the number of locked physical pages. Hence a process with two distinct locked mappings of the same physical page counts as 2 pages against the per-process limit and as only a single page in the system limit. .Sh HISTORY The .Fn mlock and .Fn munlock functions first appeared in 4.4BSD.