Provided by: freebsd-manpages_8.0-1_all
mlockall, munlockall - lock (unlock) the address space of a process
Standard C Library (libc, -lc)
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
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
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
[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
[EPERM] The calling process does not have the appropriate
privilege to perform the requested operation.
mincore(2), mlock(2), mmap(2), munmap(2), setrlimit(2)
The mlockall() and munlockall() functions are believed to conform to IEEE
Std 1003.1-2001 (“POSIX.1”).
The mlockall() and munlockall() functions first appeared in FreeBSD 5.1.
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.