mlockall
, munlockall
—
lock (unlock) the address space of a process
Standard C Library (libc, -lc)
#include <sys/mman.h>
int
mlockall
(int
flags);
int
munlockall
(void);
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.
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.
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.
The mlockall
() and munlockall
()
functions conform to IEEE Std 1003.1b-1993
(“POSIX.1b”).
The mlockall
() and munlockall
()
functions first appeared in NetBSD 1.5.
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.