linux-kernel - Re: [PATCH 1/1] mm/mm_init.c: eliminate a local variable in mem_debugging_and_hardening

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Message-ID: <5d180035-1337-fcb5-601c-75b773c20a28@huaweicloud.com>
Date: Wed, 20 Mar 2024 09:18:19 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Zhen Lei <thunder.leizhen@...wei.com>
Subject: Re: [PATCH 1/1] mm/mm_init.c: eliminate a local variable in
 mem_debugging_and_hardening_init()



On 2024/3/19 23:01, Mike Rapoport wrote:
> On Tue, Mar 19, 2024 at 09:22:03AM +0800, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2024/3/19 0:33, Mike Rapoport wrote:
>>> On Mon, Mar 18, 2024 at 09:57:14PM +0800, thunder.leizhen@...weicloud.com wrote:
>>>> From: Zhen Lei <thunder.leizhen@...wei.com>
>>>>
>>>> The local variable 'page_poisoning_requested' is assigned true at only
>>>> one point. It can be eliminated by moving the code that depends on it
>>>> to the location where it is assigned true. This also make the moved
>>>> code to be compiled only if CONFIG_PAGE_POISONING is set.
>>>
>>> I don't see it as much of an improvement and code readability becomes worse
>>> IMO.
>>
>> Yes, the moved branch will be optimized by the compiler if CONFIG_PAGE_POISONING is
>> not set. But for a reader, he can simply skip over that moved branch when
>> CONFIG_PAGE_POISONING is not set.
> 
> Saving one branch at init does not justify the churn and reduced
> readability. 

OK, I got it.

>   
>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>>> ---
>>>>  mm/mm_init.c | 17 +++++++----------
>>>>  1 file changed, 7 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>>>> index 549e76af8f82a8e..3eb217130bcb2b5 100644
>>>> --- a/mm/mm_init.c
>>>> +++ b/mm/mm_init.c
>>>> @@ -2614,7 +2614,6 @@ DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
>>>>   */
>>>>  static void __init mem_debugging_and_hardening_init(void)
>>>>  {
>>>> -	bool page_poisoning_requested = false;
>>>>  	bool want_check_pages = false;
>>>>  
>>>>  #ifdef CONFIG_PAGE_POISONING
>>>> @@ -2626,18 +2625,16 @@ static void __init mem_debugging_and_hardening_init(void)
>>>>  	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
>>>>  	      debug_pagealloc_enabled())) {
>>>>  		static_branch_enable(&_page_poisoning_enabled);
>>>> -		page_poisoning_requested = true;
>>>>  		want_check_pages = true;
>>>> -	}
>>>> -#endif
>>>>  
>>>> -	if ((_init_on_alloc_enabled_early || _init_on_free_enabled_early) &&
>>>> -	    page_poisoning_requested) {
>>>> -		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
>>>> -			"will take precedence over init_on_alloc and init_on_free\n");
>>>> -		_init_on_alloc_enabled_early = false;
>>>> -		_init_on_free_enabled_early = false;
>>>> +		if (_init_on_alloc_enabled_early || _init_on_free_enabled_early) {
>>>> +			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
>>>> +				"will take precedence over init_on_alloc and init_on_free\n");
>>>> +			_init_on_alloc_enabled_early = false;
>>>> +			_init_on_free_enabled_early = false;
>>>> +		}
>>>>  	}
>>>> +#endif
>>>>  
>>>>  	if (_init_on_alloc_enabled_early) {
>>>>  		want_check_pages = true;
>>>> -- 
>>>> 2.34.1
>>>>
>>>
>>
>> -- 
>> Regards,
>>   Zhen Lei
>>
> 

-- 
Regards,
  Zhen Lei