linux-kernel - Re: [PATCH v2 1/5] man/man2/prctl.2, PR_FUTEX_HASH_SET_SLOTS.2const: Document PR_FUTEX_HASH_SET

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Message-ID: <ueacsjksonhqg6pt6hvlav4uhfms2vrqttfez3ouryud5myhb6@uunect56gya2>
Date: Wed, 15 Oct 2025 23:29:39 +0200
From: Alejandro Colomar <alx@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-man@...r.kernel.org, 
	André Almeida <andrealmeid@...lia.com>, Darren Hart <dvhart@...radead.org>, 
	Davidlohr Bueso <dave@...olabs.net>, Ingo Molnar <mingo@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Valentin Schneider <vschneid@...hat.com>, 
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v2 1/5] man/man2/prctl.2, PR_FUTEX_HASH_SET_SLOTS.2const:
 Document PR_FUTEX_HASH_SET_SLOTS

Hi Sebastian,

Sorry for taking a month to reply.

On Mon, Sep 15, 2025 at 04:13:01PM +0200, Sebastian Andrzej Siewior wrote:
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Thanks!  I've applied the patch, and amended it with the following
change:

	diff --git c/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const i/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
	index 1605c18c6..dfd97540c 100644
	--- c/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
	+++ i/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
	@@ -27,7 +27,7 @@ .SH DESCRIPTION
	 .TP
	 .I 0
	 Use the global hash.
	-This is the behaviour used before 6.17.
	+This is the behaviour used before Linux 6.17.
	 .TP
	 .I >0
	 Specify the number of slots to allocate.

Have a lovely night!
Alex

> ---
>  man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const | 67 ++++++++++++++++++++
>  1 file changed, 67 insertions(+)
>  create mode 100644 man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
> 
> diff --git a/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const b/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
> new file mode 100644
> index 0000000000000..1605c18c6985b
> --- /dev/null
> +++ b/man/man2const/PR_FUTEX_HASH_SET_SLOTS.2const
> @@ -0,0 +1,67 @@
> +.\" Copyright, the authors of the Linux man-pages project
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH PR_FUTEX_HASH_SET_SLOTS 2const (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +PR_FUTEX_HASH_SET_SLOTS
> +\-
> +set the size of the private hash
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ,\~ \-lc )
> +.SH SYNOPSIS
> +.nf
> +.BR "#include <linux/prctl.h>" "  /* Definition of " PR_* " constants */"
> +.B #include <sys/prctl.h>
> +.P
> +.B int prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS,
> +.BI "          unsigned long " size ", unsigned long " flags ");
> +.fi
> +.SH DESCRIPTION
> +Set the number of slots to use for the private hash.
> +.TP
> +.I size
> +Specify the size of private hash to allocate.
> +.RS
> +.TP
> +.I 0
> +Use the global hash.
> +This is the behaviour used before 6.17.
> +.TP
> +.I >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
> +.I CONFIG_PROVE_LOCKING
> +will consume more than that.
> +.RE
> +.TP
> +.I flags
> +.RS
> +The argument must be 0.
> +.SH RETURN VALUE
> +On success,
> +0 is returned.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EINVAL
> +An argument is invalid.
> +.TP
> +.B ENOMEM
> +Failed to allocate memory.
> +.TP
> +.B EBUSY
> +The global hash is in use and can not be changed.
> +.SH STANDARDS
> +Linux.
> +.SH HISTORY
> +Linux 6.17.
> +.SH SEE ALSO
> +.BR prctl (2),
> +.BR PR_FUTEX_HASH (2const)
> -- 
> 2.51.0
> 

-- 
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).

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