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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 are believed to conform to IEEE Std 1003.1-2001
     (“POSIX.1”).

HISTORY

     The mlockall() and munlockall() functions first appeared in FreeBSD 5.1.

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.