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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.

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.
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

An argument is invalid.
Failed to allocate memory.
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)

2025-10-15 Linux man-pages (unreleased)