MLOCKALL(3P)

📦 version 2017a, in alpine 3.22, alpine 3.23, alpine 3.24, arch rolling, nixpkgs unstable, opensuse-leap 16.0

👑 MLOCKALL(3P) 👑 — bestie edition

okay so this is the POSIX Programmer's Manual page for mlockall and munlockall, section 3P. sit down, hydrate, let's lock some memory together 💖

🌸 PROLOG 🌸

real talk: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so pls go consult the corresponding Linux manual page for details of Linux behavior), or honestly the interface may not even be implemented on Linux at all. no cap. 🙈

✨ NAME ✨

mlockall, munlockall — lock/unlock the address space of a process (REALTIME)

🎀 SYNOPSIS 🎀

#include <sys/mman.h>

int mlockall(int flags);
int munlockall(void);

💅 DESCRIPTION 💅

so what mlockall() does is it shall cause all of the pages mapped by the address space of a process to be memory-resident until they get unlocked, or until the process exits, or until it execs another process image. iconic behavior honestly.

the flags argument is the vibe check that decides which pages get locked:

  • those currently mapped by the address space of the process,
  • those that are mapped in the future,
  • or literally both. 💫

the flags argument is constructed from the bitwise-inclusive OR of one or more of the following symbolic constants, defined in <sys/mman.h>:

  • MCL_CURRENT — lock all of the pages currently mapped into the address space of the process.
  • MCL_FUTURE — lock all of the pages that become mapped into the address space of the process in the future, when those mappings are established.
⚠️ heads up: if MCL_FUTURE is specified, and the automatic locking of future mappings eventually causes the amount of locked memory to exceed the amount of available physical memory (or any other implementation-defined limit), the behavior is implementation-defined. the manner in which the implementation informs the application of these situations is also implementation-defined. so like… it's giving "your mileage may vary" 😭

now munlockall() shall unlock all currently mapped pages of the address space of the process. any pages that become mapped into the address space of the process after a call to munlockall() shall not be locked — unless there's an intervening call to mlockall() specifying MCL_FUTURE, or a subsequent call to mlockall() specifying MCL_CURRENT. got it? 💜

also, if pages mapped into the address space of the process are also mapped into the address spaces of other processes and are locked by those processes, the locks established by the other processes shall be unaffected by a call by this process to munlockall(). their locks, their business. 🫶

upon successful return from the mlockall() function that specifies MCL_CURRENT, all currently mapped pages of the address space of the process shall be memory-resident and locked. upon return from the munlockall() function, all currently mapped pages of the address space of the process shall be unlocked with respect to the address space of the process. the memory residency of unlocked pages is unspecified. 🙃

appropriate privileges are required to lock process memory with mlockall(). yes, it's that kind of party. 👑

⭐ RETURN VALUE ⭐

upon successful completion, the mlockall() function shall return a value of zero. otherwise, no additional memory shall be locked, and the function shall return a value of -1 and set errno to indicate the error. the effect of failure of mlockall() on previously existing locks in the address space is unspecified.

if it is supported by the implementation, the munlockall() function shall always return a value of zero. otherwise, the function shall return a value of -1 and set errno to indicate the error.

💀 ERRORS 💀

the mlockall() function shall fail if:

  • EAGAIN — some or all of the memory identified by the operation could not be locked when the call was made.
  • EINVAL — the flags argument is zero, or includes unimplemented flags.

the mlockall() function may fail if:

  • ENOMEM — locking all of the pages currently mapped into the address space of the process would exceed an implementation-defined limit on the amount of memory that the process may lock.
  • EPERM — the calling process does not have appropriate privileges to perform the requested operation.

the following sections are informative.

🌈 EXAMPLES 🌈

None. (yes, fr fr. nothing here. moving on 🦋)

🍓 APPLICATION USAGE 🍓

None.

🧚 RATIONALE 🧚

None.

🔥 FUTURE DIRECTIONS 🔥

None.

💖 SEE ALSO 💖

exec, exit(), fork(), mlock(), munmap()

The Base Definitions volume of POSIX.1‐2017, <sys_mman.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

and that's the whole page bestie 💅 this was brought to you by IEEE/The Open Group, dated 2017, and filed under MLOCKALL(3P). now go lock some pages (responsibly, with appropriate privileges) 🎀✨

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