NAME
mlockall,
munlockall —
lock (unlock) the address space of a process
LIBRARY
Standard C Library (libc, -lc)
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
A return value of 0 indicates that the call succeeded and all pages in the range
have either been locked or unlocked. 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
errno is set to indicate
the error.
ERRORS
mlockall() will fail if:
-
-
- [
EINVAL
]
- The flags argument is zero, or
includes unimplemented flags.
-
-
- [
ENOMEM
]
- Locking the indicated range 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 privilege
to perform the requested operation.
SEE ALSO
mincore(2),
mlock(2),
mmap(2),
munmap(2),
setrlimit(2)
STANDARDS
The
mlockall() and
munlockall() functions
conform to
IEEE Std 1003.1b-1993
(“POSIX.1b”).
HISTORY
The
mlockall() and
munlockall() functions
first appeared in
NetBSD 1.5.
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 as only a single page
in the system limit.