PR_FUTEX_HASH_SET_SLOTS(2const) — Linux manual page

PR_FUTEX_HASH_SET_SLOTS(2const)           PR_FUTEX_HASH_SET_SLOTS(2const)

NAME         top

       PR_FUTEX_HASH_SET_SLOTS - set the size of the private hash

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <linux/prctl.h>  /* Definition of PR_* constants */
       #include <sys/prctl.h>

       int prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS,
                 unsigned long size, unsigned long flags);

DESCRIPTION         top

       Set the number of slots to use for the private hash.

       size   Specify the size of private hash to allocate.

              0      Use the global hash.  This is the behaviour used
                     before Linux 6.17.

              >0     Specify the number of slots to allocate.  The value
                     must be power of two, and the lowest possible value
                     is 2.  The upper limit depends on the available
                     memory in the system.  Each slot requires 64 bytes
                     of memory.  Kernels compiled with
                     CONFIG_PROVE_LOCKING will consume more than that.

       flags
              The argument must be 0.

RETURN VALUE         top

       On success, 0 is returned.  On error, -1 is returned, and errno is
       set to indicate the error.

ERRORS         top

       EINVAL An argument is invalid.

       ENOMEM Failed to allocate memory.

       EBUSY  The global hash is in use and can not be changed.

STANDARDS         top

       Linux.

HISTORY         top

       Linux 6.17.

SEE ALSO         top

       prctl(2), PR_FUTEX_HASH(2const)

COLOPHON         top

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Linux man-pages 6.16            2025-10-15PR_FUTEX_HASH_SET_SLOTS(2const)

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