linux-kernel - Re: [PATCH v2 1/2] sysctl: remove empty dev table

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Message-ID: <20230601053534.272v4berfml7vytz@localhost>
Date:   Thu, 1 Jun 2023 07:35:34 +0200
From:   Joel Granados <j.granados@...sung.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
CC:     <ebiederm@...ssion.com>, <keescook@...omium.org>,
        <yzaikin@...gle.com>, <dave.hansen@...el.com>, <arnd@...db.de>,
        <bp@...en8.de>, <James.Bottomley@...senpartnership.com>,
        <deller@....de>, <tglx@...utronix.de>, <mingo@...hat.com>,
        <x86@...nel.org>, <hpa@...or.com>, <luto@...nel.org>,
        <peterz@...radead.org>, <brgerst@...il.com>,
        <christophe.jaillet@...adoo.fr>, <kirill.shutemov@...ux.intel.com>,
        <jroedel@...e.de>, <akpm@...ux-foundation.org>,
        <willy@...radead.org>, <linux-parisc@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] sysctl: remove empty dev table

On Tue, May 30, 2023 at 03:55:10PM -0700, Luis Chamberlain wrote:
> On Tue, May 30, 2023 at 09:42:04AM -0700, Luis Chamberlain wrote:
> > On Mon, May 29, 2023 at 10:04:57PM +0200, Joel Granados wrote:
> > > On Fri, May 26, 2023 at 03:22:05PM -0700, Luis Chamberlain wrote:
> > > > Now that all the dev sysctls have been moved out we can remove the
> > > > dev sysctl base directory. We don't need to create base directories,
> > > > they are created for you as if using 'mkdir -p' with register_syctl()
> > > > and register_sysctl_init(). For details refer to sysctl_mkdir_p()
> > > > usage.
> > > > 
> > > > We save 90 bytes with this changes:
> > > > 
> > > > ./scripts/bloat-o-meter vmlinux.2.remove-sysctl-table vmlinux.3-remove-dev-table
> > > > add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-90 (-90)
> > > > Function                                     old     new   delta
> > > > sysctl_init_bases                            111      85     -26
> > > > dev_table                                     64       -     -64
> > > > Total: Before=21257057, After=21256967, chg -0.00%
> > > > 
> > > > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > > > ---
> > > >  kernel/sysctl.c | 5 -----
> > > >  1 file changed, 5 deletions(-)
> > > > 
> > > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > > > index fa2aa8bd32b6..a7fdb828afb6 100644
> > > > --- a/kernel/sysctl.c
> > > > +++ b/kernel/sysctl.c
> > > > @@ -2344,16 +2344,11 @@ static struct ctl_table debug_table[] = {
> > > >  	{ }
> > > >  };
> > > >  
> > > > -static struct ctl_table dev_table[] = {
> > > > -	{ }
> > > > -};
> > > > -
> > > >  int __init sysctl_init_bases(void)
> > > >  {
> > > >  	register_sysctl_init("kernel", kern_table);
> > > >  	register_sysctl_init("vm", vm_table);
> > > >  	register_sysctl_init("debug", debug_table);
> > > > -	register_sysctl_init("dev", dev_table);
> > > >  
> > > >  	return 0;
> > > >  }
> > > > -- 
> > > > 2.39.2
> > > > 
> > > LGTM.
> > 
> > BTW, please use proper tags like Reviewed-by, and so on even if you use
> > LGTM so that then if anyone uses things like b4 it can pick the tags for
> > you.
> > 
> > > But why was dev there to begin with?
> > 
> > I will enhance the commit log to mention that, it was there because
> > old APIs didn't create the directory for you, and now it is clear it
> > is not needed. I checked ant he dev table was there since the beginning
> > of sysctl.c on v2.5.0.
> 
> I've extended the commmit log with this very importance piece of
> information:
Awesome!

> 
> The empty dev table has been in place since the v2.5.0 days because back
> then ordering was essentialy. But later commit 7ec66d06362d ("sysctl:
*essential ?

> Stop requiring explicit management of sysctl directories"), merged as of
> v3.4-rc1, the entire ordering of directories was replaced by allowing
> sysctl directory autogeneration. This new mechanism introduced on v3.4
> allows for sysctl directories to automatically be created for sysctl
> tables when they are needed and automatically removes them when no
> sysctl tables use them.  That commit also added a dedicated struct
> ctl_dir as a new type for these autogenerated directories.
> 
>   Luis

-- 

Joel Granados

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