MLOCKALL(2) BSD System Calls Manual MLOCKALL(2)
mlockall, munlockall -- lock (unlock) the address space of a process
The mlockall() system call locks into memory the physical pages associ-
ated 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 map-
pings 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
The mlockall() and munlockall() functions return the value 0 if success-
ful; otherwise the value -1 is returned and the global variable errno is
set to indicate the error.
mlockall() will fail if:
[EINVAL] The flags argument is zero or includes unimplemented
[ENOMEM] Locking all of the pages currently mapped would exceed
either the system or per-process limit for locked mem-
[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
privileges to perform the requested operation.
mincore(2), mlock(2), mmap(2), munmap(2), setrlimit(2)
The mlockall() and munlockall() functions conform to IEEE Std 1003.1-2008
The mlockall() and munlockall() functions first appeared in OpenBSD 2.9.
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.
BSD March 27, 2017 BSD