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

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Date:   Thu, 29 Apr 2021 18:05:56 +0800
From:   Coly Li <colyli@...e.de>
To:     Muhammad Usama Anjum <musamaanjum@...il.com>,
        Zheng Yongjun <zhengyongjun3@...wei.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     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 4/29/21 12:19 AM, Muhammad Usama Anjum wrote:
> 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?
> 
> 


I am waiting for Yongjun's v4 patch to update the commit log, which was
suggested by Pavel Goran.

Coly Li