linux-kernel - Re: [PATCH] mm/slub: Refactor note_cmpxchg

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Message-ID: <f7728a4a-7af9-4d7b-a06d-d61b697eaeef@linux.dev>
Date: Mon, 8 Sep 2025 17:33:57 +0800
From: Ye Liu <ye.liu@...ux.dev>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
 Andrew Morton <akpm@...ux-foundation.org>, Ye Liu <liuye@...inos.cn>,
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>,
 Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: Refactor note_cmpxchg_failure for better
 readability



在 2025/9/8 17:21, Harry Yoo 写道:
> On Mon, Sep 08, 2025 at 04:56:40PM +0800, Ye Liu wrote:
>>
>>
>> 在 2025/9/8 16:39, Harry Yoo 写道:
>>> On Mon, Sep 08, 2025 at 03:19:21PM +0800, Ye Liu wrote:
>>>> From: Ye Liu <liuye@...inos.cn>
>>>>
>>>> Use IS_ENABLED() and standard if-else to make the code clearer.
>>>>
>>>> Signed-off-by: Ye Liu <liuye@...inos.cn>
>>>> ---
>>>
>>> Looks good to me,
>>> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
>>>
>>> with a nit,
>>>
>>>>  mm/slub.c | 10 ++++------
>>>>  1 file changed, 4 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/mm/slub.c b/mm/slub.c
>>>> index 30003763d224..34853c0441a6 100644
>>>> --- a/mm/slub.c
>>>> +++ b/mm/slub.c
>>>> @@ -3064,18 +3064,16 @@ static inline void note_cmpxchg_failure(const char *n,
>>>>  
>>>>  	pr_info("%s %s: cmpxchg redo ", n, s->name);
>>>>  
>>>> -#ifdef CONFIG_PREEMPTION
>>>> -	if (tid_to_cpu(tid) != tid_to_cpu(actual_tid))
>>>> +	if (IS_ENABLED(CONFIG_PREEMPTION) && tid_to_cpu(tid) != tid_to_cpu(actual_tid)) {
>>>
>>> nit: insert newline after && as it's more than 80 columns?
>>
>> I noticed this too, but using the script ./scripts/checkpatch.pl , there were no warnings.
>>
>> $ ./scripts/checkpatch.pl 0001-mm-slub-Refactor-note_cmpxchg_failure-for-better-rea.patch 
>> total: 0 errors, 0 warnings, 22 lines checked
>>
>> 0001-mm-slub-Refactor-note_cmpxchg_failure-for-better-rea.patch has no obvious style problems and is ready for submission.
> 
> IIUC the default limit is increased to 100 characters in checkpatch
> but 80 characters is still preferred.
Thank you for your patience.
I will update the V2 version and include your Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> 
> Quoting Documentation/process/coding-style.rst:
> 
> 2) Breaking long lines and strings
> ----------------------------------
> 
> Coding style is all about readability and maintainability using commonlu
> available tools.
> 
> The preferred limit on the length of a single line is 80 columns.
> 
> Statements longer than 80 columns should be broken into sensible chunks,
> unless exceeding 80 columns significantly increases readability and does
> not hide information.
> 
> Descendants are always substantially shorter than the parent and                
> are placed substantially to the right.  A very commonly used style              
> is to align descendants to a function open parenthesis.                         
> 
> These same rules are applied to function headers with a long argument list.
> 
> However, never break user-visible strings such as printk messages because
> that breaks the ability to grep for them. 
> 
> And also quoting a commit message:
> 
> commit bdc48fa11e46f867ea4d75fa59ee87a7f48be144
> Author: Joe Perches <joe@...ches.com>
> Date:   Fri May 29 16:12:21 2020 -0700
> 
>     checkpatch/coding-style: deprecate 80-column warning
> 
>     Yes, staying withing 80 columns is certainly still _preferred_.  But
>     it's not the hard limit that the checkpatch warnings imply, and other
>     concerns can most certainly dominate.
> 
>     Increase the default limit to 100 characters.  Not because 100
>     characters is some hard limit either, but that's certainly a "what are
>     you doing" kind of value and less likely to be about the occasional
>     slightly longer lines.
> 
>     Miscellanea:
> 
>      - to avoid unnecessary whitespace changes in files, checkpatch will no
>        longer emit a warning about line length when scanning files unless
>        --strict is also used
> 
>      - Add a bit to coding-style about alignment to open parenthesis
> 
>     Signed-off-by: Joe Perches <joe@...ches.com>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> 
>>>>  		pr_warn("due to cpu change %d -> %d\n",
>>>>  			tid_to_cpu(tid), tid_to_cpu(actual_tid));
>>>> -	else
>>>> -#endif
>>>> -	if (tid_to_event(tid) != tid_to_event(actual_tid))
>>>> +	} else if (tid_to_event(tid) != tid_to_event(actual_tid)) {
>>>>  		pr_warn("due to cpu running other code. Event %ld->%ld\n",
>>>>  			tid_to_event(tid), tid_to_event(actual_tid));
>>>> -	else
>>>> +	} else {
>>>>  		pr_warn("for unknown reason: actual=%lx was=%lx target=%lx\n",
>>>>  			actual_tid, tid, next_tid(tid));
>>>> +	}
>>>>  #endif
>>>>  	stat(s, CMPXCHG_DOUBLE_CPU_FAIL);
>>>>  }
>>>> -- 
>>>> 2.43.0
>>
>> -- 
>> Thanks,
>> Ye Liu
>>
>>
> 

-- 
Thanks,
Ye Liu