f0eaf8ec5e
User wirings of the same address range don't stack. Noted by: Dan Nelson MFC after: 3 days
182 lines
5.6 KiB
Groff
182 lines
5.6 KiB
Groff
.\" 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. 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
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd March 20, 2018
|
|
.Dt MLOCK 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mlock ,
|
|
.Nm munlock
|
|
.Nd lock (unlock) physical pages in memory
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/mman.h
|
|
.Ft int
|
|
.Fn mlock "const void *addr" "size_t len"
|
|
.Ft int
|
|
.Fn munlock "const void *addr" "size_t len"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn mlock
|
|
system call
|
|
locks into memory the physical pages associated with the virtual address
|
|
range starting at
|
|
.Fa addr
|
|
for
|
|
.Fa len
|
|
bytes.
|
|
The
|
|
.Fn munlock
|
|
system call unlocks pages previously locked by one or more
|
|
.Fn mlock
|
|
calls.
|
|
For both, the
|
|
.Fa addr
|
|
argument should be aligned to a multiple of the page size.
|
|
If the
|
|
.Fa len
|
|
argument 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
|
|
.Fn mlock
|
|
system 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.
|
|
Multiple processes may have the same physical pages locked via their own
|
|
virtual address mappings.
|
|
A single process may likewise have pages multiply-locked via different virtual
|
|
mappings of the same physical pages.
|
|
Unlocking is performed explicitly by
|
|
.Fn munlock
|
|
or implicitly by a call to
|
|
.Fn munmap
|
|
which deallocates the unmapped address range.
|
|
Locked mappings are not inherited by the child process after a
|
|
.Xr fork 2 .
|
|
.Pp
|
|
Since physical memory is a potentially scarce resource, processes are
|
|
limited in how much they can lock down.
|
|
The amount of memory that a single process can
|
|
.Fn mlock
|
|
is limited by both the per-process
|
|
.Dv RLIMIT_MEMLOCK
|
|
resource limit and the
|
|
system-wide
|
|
.Dq wired pages
|
|
limit
|
|
.Va vm.max_wired .
|
|
.Va vm.max_wired
|
|
applies to the system as a whole, so the amount available to a single
|
|
process at any given time is the difference between
|
|
.Va vm.max_wired
|
|
and
|
|
.Va vm.stats.vm.v_wire_count .
|
|
.Pp
|
|
If
|
|
.Va security.bsd.unprivileged_mlock
|
|
is set to 0 these calls are only available to the super-user.
|
|
.Sh RETURN VALUES
|
|
.Rv -std
|
|
.Pp
|
|
If the call succeeds, all pages in the range become locked (unlocked);
|
|
otherwise the locked status of all pages in the range remains unchanged.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn mlock
|
|
system call
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EPERM
|
|
.Va security.bsd.unprivileged_mlock
|
|
is set to 0 and the caller is not the super-user.
|
|
.It Bq Er EINVAL
|
|
The address range given wraps around zero.
|
|
.It Bq Er EAGAIN
|
|
Locking the indicated range would exceed the system 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.
|
|
Locking the indicated range would exceed the per-process limit for locked
|
|
memory.
|
|
.El
|
|
The
|
|
.Fn munlock
|
|
system call
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EPERM
|
|
.Va security.bsd.unprivileged_mlock
|
|
is set to 0 and the caller is not the super-user.
|
|
.It Bq Er EINVAL
|
|
The address range given wraps around zero.
|
|
.It Bq Er ENOMEM
|
|
Some or all of the address range specified by the addr and len
|
|
arguments does not correspond to valid mapped pages in the address space
|
|
of the process.
|
|
.It Bq Er ENOMEM
|
|
Locking the pages mapped by the specified range would exceed a limit on
|
|
the amount of memory that the process may lock.
|
|
.El
|
|
.Sh "SEE ALSO"
|
|
.Xr fork 2 ,
|
|
.Xr mincore 2 ,
|
|
.Xr minherit 2 ,
|
|
.Xr mlockall 2 ,
|
|
.Xr mmap 2 ,
|
|
.Xr munlockall 2 ,
|
|
.Xr munmap 2 ,
|
|
.Xr setrlimit 2 ,
|
|
.Xr getpagesize 3
|
|
.Sh HISTORY
|
|
The
|
|
.Fn mlock
|
|
and
|
|
.Fn munlock
|
|
system calls first appeared in
|
|
.Bx 4.4 .
|
|
.Sh BUGS
|
|
Allocating too much wired memory can lead to a memory-allocation deadlock
|
|
which requires a reboot to recover from.
|
|
.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.
|
|
.Pp
|
|
The per-process resource limit is not currently supported.
|