170 lines
5.3 KiB
Groff
170 lines
5.3 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mlock.2 8.2 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd August 10, 2004
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.Dt MLOCK 2
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.Os
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.Sh NAME
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.Nm mlock ,
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.Nm munlock
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.Nd lock (unlock) physical pages in memory
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/mman.h
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.Ft int
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.Fn mlock "const void *addr" "size_t len"
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.Ft int
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.Fn munlock "const void *addr" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn mlock
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system call
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locks into memory the physical pages associated with the virtual address
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range starting at
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.Fa addr
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for
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.Fa len
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bytes.
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The
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.Fn munlock
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system call unlocks pages previously locked by one or more
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.Fn mlock
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calls.
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For both, the
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.Fa addr
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argument should be aligned to a multiple of the page size.
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If the
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.Fa len
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argument is not a multiple of the page size, it will be rounded up
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to be so.
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The entire range must be allocated.
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.Pp
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After an
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.Fn mlock
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system call, the indicated pages will cause neither a non-resident page
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nor address-translation fault until they are unlocked.
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They may still cause protection-violation faults or TLB-miss faults on
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architectures with software-managed TLBs.
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The physical pages remain in memory until all locked mappings for the pages
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are removed.
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Multiple processes may have the same physical pages locked via their own
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virtual address mappings.
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A single process may likewise have pages multiply-locked via different virtual
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mappings of the same pages or via nested
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.Fn mlock
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calls on the same address range.
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Unlocking is performed explicitly by
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.Fn munlock
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or implicitly by a call to
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.Fn munmap
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which deallocates the unmapped address range.
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Locked mappings are not inherited by the child process after a
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.Xr fork 2 .
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.Pp
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Since physical memory is a potentially scarce resource, processes are
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limited in how much they can lock down.
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A single process can
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.Fn mlock
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the minimum of
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a system-wide ``wired pages'' limit and
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the per-process
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.Li RLIMIT_MEMLOCK
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resource limit.
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.Pp
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These calls are only available to the super-user.
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.Sh RETURN VALUES
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.Rv -std
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.Pp
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If the call succeeds, all pages in the range become locked (unlocked);
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otherwise the locked status of all pages in the range remains unchanged.
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.Sh ERRORS
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The
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.Fn mlock
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The caller is not the super-user.
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.It Bq Er EINVAL
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The address given is not page aligned or the length is negative.
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.It Bq Er EAGAIN
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Locking the indicated range would exceed either the system or per-process
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limit for locked memory.
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.It Bq Er ENOMEM
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Some portion of the indicated address range is not allocated.
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There was an error faulting/mapping a page.
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.El
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The
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.Fn munlock
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The caller is not the super-user.
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.It Bq Er EINVAL
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The address given is not page aligned or the length is negative.
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.It Bq Er ENOMEM
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Some portion of the indicated address range is not allocated.
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.El
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.Sh "SEE ALSO"
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.Xr mlockall 2 ,
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.Xr munlockall 2 ,
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.Xr fork 2 ,
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.Xr mincore 2 ,
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.Xr minherit 2 ,
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.Xr mmap 2 ,
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.Xr munmap 2 ,
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.Xr setrlimit 2 ,
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.Xr getpagesize 3
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.Sh BUGS
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Allocating too much wired memory can lead to a memory-allocation deadlock
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which requires a reboot to recover from.
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.Pp
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The per-process resource limit is a limit on the amount of virtual
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memory locked, while the system-wide limit is for the number of locked
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physical pages.
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Hence a process with two distinct locked mappings of the same physical page
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counts as 2 pages against the per-process limit and as only a single page
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in the system limit.
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.Pp
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The per-process resource limit is not currently supported.
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.Sh HISTORY
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The
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.Fn mlock
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and
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.Fn munlock
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system calls first appeared in
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.Bx 4.4 .
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