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

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Date: Tue, 19 Mar 2024 17:01:38 +0200
From: Mike Rapoport <rppt@...nel.org>
To: "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
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 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. 
  
> >> 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
> 

-- 
Sincerely yours,
Mike.