fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
184 lines
5.7 KiB
Groff
184 lines
5.7 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. 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 May 17, 2014
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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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The amount of memory that a single process can
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.Fn mlock
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is limited by both the per-process
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.Dv RLIMIT_MEMLOCK
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resource limit and the
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system-wide
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.Dq wired pages
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limit
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.Va vm.max_wired .
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.Va vm.max_wired
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applies to the system as a whole, so the amount available to a single
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process at any given time is the difference between
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.Va vm.max_wired
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and
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.Va vm.stats.vm.v_wire_count .
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.Pp
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If
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.Va security.bsd.unprivileged_mlock
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is set to 0 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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.Va security.bsd.unprivileged_mlock
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is set to 0 and 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 the system 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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Locking the indicated range would exceed the per-process limit for locked
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memory.
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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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.Va security.bsd.unprivileged_mlock
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is set to 0 and 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 or all of the address range specified by the addr and len
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arguments does not correspond to valid mapped pages in the address space
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of the process.
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.It Bq Er ENOMEM
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Locking the pages mapped by the specified range would exceed a limit on
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the amount of memory that the process may lock.
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.El
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.Sh "SEE ALSO"
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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 mlockall 2 ,
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.Xr mmap 2 ,
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.Xr munlockall 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 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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.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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