PR_FUTEX_HASH_SET_SLOTS(2const)                PR_FUTEX_HASH_SET_SLOTS(2const)

NAME
       PR_FUTEX_HASH_SET_SLOTS - set the size of the private hash

LIBRARY
       Standard C library (libc, -lc)

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

ERRORS
       EINVAL An argument is invalid.

       ENOMEM Failed to allocate memory.

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

STANDARDS
       Linux.

HISTORY
       Linux 6.17.

SEE ALSO
       prctl(2), PR_FUTEX_HASH(2const)

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