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: <5fd9144b-fb1c-08fc-8124-1972f86253a4@huaweicloud.com>
Date: Tue, 19 Mar 2024 09:22:03 +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 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.

>  
>> 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