linux-kernel - Re: [PATCH -next] bcache: use DEFINE

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Message-ID: <0b4b7c5cc2f19d2d77a66c0d2ce42f63692174d9.camel@gmail.com>
Date:   Wed, 28 Apr 2021 21:19:26 +0500
From:   Muhammad Usama Anjum <musamaanjum@...il.com>
To:     Coly Li <colyli@...e.de>, Zheng Yongjun <zhengyongjun3@...wei.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     musamaanjum@...il.com, linux-bcache@...r.kernel.org,
        kernel-janitors@...r.kernel.org, Hulk Robot <hulkci@...wei.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] bcache: use DEFINE_MUTEX() for mutex lock

On Tue, 2021-04-06 at 02:17 +0500, Muhammad Usama Anjum wrote:
> On Mon, 2021-04-05 at 22:02 +0800, Coly Li wrote:
> > On 4/5/21 6:14 PM, Zheng Yongjun wrote:
> > > mutex lock can be initialized automatically with DEFINE_MUTEX()
> > > rather than explicitly calling mutex_init().
> > > 
> > > Reported-by: Hulk Robot <hulkci@...wei.com>
> > > Signed-off-by: Zheng Yongjun <zhengyongjun3@...wei.com>
> > 
> > NACK. This is not the first time people try to "fix" this location...
> > 
> > Using DEFINE_MUTEX() does not gain anything for us, it will generate
> > unnecessary extra size for the bcache.ko.
> > ines.
> 
> How can the final binary have larger size by just static declaration?
> By using DEFINE_MUTEX, the mutex is initialized at compile time. It'll
> save initialization at run time and one line of code will be less also
> from text section. 
> 
> #### with no change (dynamic initialization)
> size drivers/md/bcache/bcache.ko
>    text	   data	    bss	    dec	    hex	filename
>  187792	  25310	    152	 213254	  34106	drivers/md/bcache/bcache.ko
> 
> #### with patch applied (static initialization)
>    text	   data	    bss	    dec	    hex	filename
>  187751	  25342	    120	 213213	  340dd	drivers/md/bcache/bcache.ko
> 
> Module's binary size has decreased by 41 bytes with the path applied
> (x86_64 arch).
> 
Anybody has any thoughts on it?