Re: [PATCH 08/11] sysctl: Add size to register_sysctl_init

From: Petr Mladek <pmladek@suse.com>
To: Joel Granados <j.granados@samsung.com>
Cc: mcgrof@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, Theodore Ts'o <tytso@mit.edu>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Juergen Gross <jgross@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Benjamin LaHaise <bcrl@kvack.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Jeff Layton <jlayton@kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>, Jan Kara <jack@suse.cz>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Eric Biederman <ebiederm@xmission.com>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Muchun Song <muchun.song@linux.dev>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	David Howells <dhowells@redhat.com>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
	Amir Goldstein <amir73il@gmail.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>, Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	John Ogness <john.ogness@linutronix.de>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Will Drewry <wad@chromium.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, bpf@vger.kernel.org,
	kexec@lists.infradead.org, linux-trace-kernel@vger.kernel.org,
	keyrings@vger.kernel.org, linux-security-module@vger.kernel.org
Subject: Re: [PATCH 08/11] sysctl: Add size to register_sysctl_init
Date: Wed, 21 Jun 2023 13:36:46 +0200	[thread overview]
Message-ID: <ZJLgzo1GuykDV8fd@alley> (raw)
In-Reply-To: <20230621091000.424843-9-j.granados@samsung.com>

On Wed 2023-06-21 11:09:57, Joel Granados wrote:
> In order to remove the end element from the ctl_table struct arrays, we
> explicitly define the size when registering the targes. We add a size
> argument to the register_sysctl_init call and pass an ARRAY_SIZE for all
> the callers.

This does not explain the motivatin why the end element is removed.

I agree with Jiri that saving 9k is a questionable gain. According to
the cover letter it saved 0,00%. It is because it saved 9k with allyes
config which produces huge kernel. IMHO, the 9k might be interesting
only for a tiny kernel. But I guess that it would safe much less
bytes there.

And the code with the added ARRAY_SIZE() parameter looks worse than before.

> diff --git a/kernel/printk/sysctl.c b/kernel/printk/sysctl.c
> index c228343eeb97..28f37b86414e 100644
> --- a/kernel/printk/sysctl.c
> +++ b/kernel/printk/sysctl.c
> @@ -81,5 +81,6 @@ static struct ctl_table printk_sysctls[] = {
>  
>  void __init printk_sysctl_init(void)
>  {
> -	register_sysctl_init("kernel", printk_sysctls);
> +	register_sysctl_init("kernel", printk_sysctls,
> +			     ARRAY_SIZE(printk_sysctls));
>  }

Is register_sysctl_init() still ready to handle the last empty element,
please? I am not in Cc on the related patches.

Best Regards,
Petr