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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.