NAME
mlockall,
munlockall —
lock (unlock) the address space of a
process
SYNOPSIS
#include
<sys/mman.h>
int
mlockall(int
flags);
int
munlockall(void);
DESCRIPTION
The
mlockall()
system call locks into memory the physical pages associated with the address
space of a process until the address space is unlocked, the process exits,
or execs another program image.
The following flags affect the behavior of
mlockall():
MCL_CURRENT- Lock all pages currently mapped into the process's address space.
MCL_FUTURE- Lock all pages mapped into the process's address space in the future, at the time the mapping is established. Note that this may cause future mappings to fail if those mappings cause resource limits to be exceeded.
Since physical memory is a potentially scarce resource, processes
are limited in how much they can lock down. A single process can lock the
minimum of a system-wide “wired pages” limit and the
per-process RLIMIT_MEMLOCK resource limit.
The
munlockall()
call unlocks any locked memory regions in the process address space. Any
regions mapped after an munlockall() call will not
be locked.
RETURN VALUES
The mlockall() and
munlockall() functions return the value 0 if
successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
ERRORS
mlockall() will fail if:
- [
EINVAL] - The flags argument is zero or includes unimplemented flags.
- [
ENOMEM] - Locking all of the pages currently mapped would exceed either the system or per-process limit for locked memory.
- [
EAGAIN] - Some or all of the memory mapped into the process's address space could not be locked when the call was made.
- [
EPERM] - The calling process does not have the appropriate privileges to perform the requested operation.
SEE ALSO
STANDARDS
The mlockall() and
munlockall() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
The mlockall() and
munlockall() functions first appeared in
OpenBSD 2.9.
BUGS
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 only as a single page in the system limit.