mlockall, munlockall - Locks into memory, or unlocks, all
of a specified process's pages (P1003.1b)
int mlockall ( int options);
int munlockall (void);
Realtime Library (librt.so, librt.a)
Determines whether the pages to be locked are those currently
mapped by the process's address space, those that
will be mapped in the future, or both. The options argument
is constructed as the OR of one or more of the constants,
MCL_CURRENT or MCL_FUTURE, as defined in the
<mman.h> header file.
The mlockall function causes all of the pages mapped by
the process's address space to be memory resident until
unlocked by a call to the munlockall function, until the
process exits, or until the process calls exec. MCL_CURRENT
locks all of the pages currently mapped into the process's
address space. MCL_FUTURE locks all of the pages
that become mapped into the process's address space in the
future, when those mappings are established. You can specify
MCL_CURRENT and subsequently specify MCL_FUTURE to
lock both current and future address space.
The munlockall function unlocks all currently mapped pages
of the process's address space. Any pages that become
mapped into a process's address space after a call to
munlockall are not locked unless otherwise specified by a
subsequent call to mlockall. Pages locked or mapped into
another process's address space are unaffected by this
process's call to the munlockall function.
Locking the process's pages into memory also makes the
When the pages are unlocked, the process is made swappable.
A lock is not inherited across a fork. All memory locks
established on an address by this process are removed if
an address range associated with the lock is unmapped with
a call to the munmap function.
You must have superuser privileges to call the mlockall
On a successful call to the mlockall function, a value of
0 (zero) is returned and memory is locked. On an unsuccessful
call, a value of -1 is returned, no memory is
locked, and errno is set to indicate that an error
On a successful call to the munlockall function, a value
of 0 (zero) is returned and memory is unlocked. On an
unsuccessful call, a value of -1 is returned and errno is
set to indicate that an error occurred.
The mlockall and munlockall functions fail under the following
condition: The implementation does not support this
memory locking interface.
If any of the following conditions occur, the mlockall
function fails: Some or all of the memory identified by
the operation could not be locked when the call was made.
The options argument is zero or includes unimplemented
options. Locking all of the pages currently mapped into
the process's address space exceeds an implementationdefined
limit on the amount of memory that the process may
lock. The calling process does not have the appropriate
privilege to perform the requested operation.
Functions: exec(2), _exit(2), fork(2), munmap(2)
Guide to Realtime Programming
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