[PATCH] mm/page_alloc: Consolidate unlikely handling in page_expected_state

[PATCH] mm/page_alloc: Consolidate unlikely handling in page_expected_state

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

This patch consolidates the handling of unlikely conditions in the
page_expected_state function, reducing code duplication and improving
readability.

Previously, the check_new_page_bad function contained logic to handle
__PG_HWPOISON flags, which was called from check_new_page. This patch
moves the handling of __PG_HWPOISON flags into the page_expected_state
function and removes the check_new_page_bad function. The check_new_page
function now directly calls bad_page if the page has unexpected flags.

This change simplifies the code by reducing the number of functions and
centralizing the unlikely condition handling in one place.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 mm/page_alloc.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2842da893eea..d8d04ac1d709 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -892,6 +892,13 @@ static inline bool page_expected_state(struct page *page,
 	if (unlikely(atomic_read(&page->_mapcount) != -1))
 		return false;
 
+	if (unlikely(PageHWPoison(page))) {
+		/* Don't complain about hwpoisoned pages */
+		if (PageBuddy(page))
+			__ClearPageBuddy(page);
+		return false;
+	}
+
 	if (unlikely((unsigned long)page->mapping |
 			page_ref_count(page) |
 #ifdef CONFIG_MEMCG
@@ -1586,29 +1593,16 @@ static __always_inline void page_del_and_expand(struct zone *zone,
 	account_freepages(zone, -nr_pages, migratetype);
 }
 
-static void check_new_page_bad(struct page *page)
-{
-	if (unlikely(PageHWPoison(page))) {
-		/* Don't complain about hwpoisoned pages */
-		if (PageBuddy(page))
-			__ClearPageBuddy(page);
-		return;
-	}
-
-	bad_page(page,
-		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
-}
-
 /*
  * This page is about to be returned from the page allocator
  */
 static bool check_new_page(struct page *page)
 {
-	if (likely(page_expected_state(page,
-				PAGE_FLAGS_CHECK_AT_PREP|__PG_HWPOISON)))
+	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_PREP)))
 		return false;
 
-	check_new_page_bad(page);
+	bad_page(page,
+		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
 	return true;
 }
 
-- 
2.25.1

Re: [PATCH] mm/page_alloc: Consolidate unlikely handling in page_expected_state

[Anshuman Khandual]

On 3/21/25 06:43, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> This patch consolidates the handling of unlikely conditions in the
> page_expected_state function, reducing code duplication and improving
> readability.
> 
> Previously, the check_new_page_bad function contained logic to handle
> __PG_HWPOISON flags, which was called from check_new_page. This patch
> moves the handling of __PG_HWPOISON flags into the page_expected_state
> function and removes the check_new_page_bad function. The check_new_page
> function now directly calls bad_page if the page has unexpected flags.
> 
> This change simplifies the code by reducing the number of functions and
> centralizing the unlikely condition handling in one place.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
>  mm/page_alloc.c | 26 ++++++++++----------------
>  1 file changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2842da893eea..d8d04ac1d709 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -892,6 +892,13 @@ static inline bool page_expected_state(struct page *page,
>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
>  		return false;
>  
> +	if (unlikely(PageHWPoison(page))) {
> +		/* Don't complain about hwpoisoned pages */
> +		if (PageBuddy(page))
> +			__ClearPageBuddy(page);
> +		return false;

Should this be return 'true' instead ?

Let's consider a scenario where PageHWPoison(page) is true.

Previously bad_page() was not getting called as check_new_page_bad() will
return earlier before reaching bad_page().

But now with the proposed change here page_expected_state() returns false
and hence bad_page() still gets called later on in check_new_page().

There is a change in behaviour - or am I missing something here ?

> +	}
> +
>  	if (unlikely((unsigned long)page->mapping |
>  			page_ref_count(page) |
>  #ifdef CONFIG_MEMCG
> @@ -1586,29 +1593,16 @@ static __always_inline void page_del_and_expand(struct zone *zone,
>  	account_freepages(zone, -nr_pages, migratetype);
>  }
>  
> -static void check_new_page_bad(struct page *page)
> -{
> -	if (unlikely(PageHWPoison(page))) {
> -		/* Don't complain about hwpoisoned pages */
> -		if (PageBuddy(page))
> -			__ClearPageBuddy(page);
> -		return;
> -	}
> -
> -	bad_page(page,
> -		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
> -}
> -
>  /*
>   * This page is about to be returned from the page allocator
>   */
>  static bool check_new_page(struct page *page)
>  {
> -	if (likely(page_expected_state(page,
> -				PAGE_FLAGS_CHECK_AT_PREP|__PG_HWPOISON)))
> +	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_PREP)))
>  		return false;
>  
> -	check_new_page_bad(page);
> +	bad_page(page,
> +		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
>  	return true;
>  }
> 

Re: [PATCH] mm/page_alloc: Consolidate unlikely handling in page_expected_state

[Ye Liu]

在 2025/3/21 13:40, Anshuman Khandual 写道:
>
> On 3/21/25 06:43, Ye Liu wrote:
>> From: Ye Liu <liuye@kylinos.cn>
>>
>> This patch consolidates the handling of unlikely conditions in the
>> page_expected_state function, reducing code duplication and improving
>> readability.
>>
>> Previously, the check_new_page_bad function contained logic to handle
>> __PG_HWPOISON flags, which was called from check_new_page. This patch
>> moves the handling of __PG_HWPOISON flags into the page_expected_state
>> function and removes the check_new_page_bad function. The check_new_page
>> function now directly calls bad_page if the page has unexpected flags.
>>
>> This change simplifies the code by reducing the number of functions and
>> centralizing the unlikely condition handling in one place.
>>
>> Signed-off-by: Ye Liu <liuye@kylinos.cn>
>> ---
>>  mm/page_alloc.c | 26 ++++++++++----------------
>>  1 file changed, 10 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 2842da893eea..d8d04ac1d709 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -892,6 +892,13 @@ static inline bool page_expected_state(struct page *page,
>>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
>>  		return false;
>>  
>> +	if (unlikely(PageHWPoison(page))) {
>> +		/* Don't complain about hwpoisoned pages */
>> +		if (PageBuddy(page))
>> +			__ClearPageBuddy(page);
>> +		return false;
> Should this be return 'true' instead ?
>
> Let's consider a scenario where PageHWPoison(page) is true.
>
> Previously bad_page() was not getting called as check_new_page_bad() will
> return earlier before reaching bad_page().
>
> But now with the proposed change here page_expected_state() returns false
> and hence bad_page() still gets called later on in check_new_page().
>
> There is a change in behaviour - or am I missing something here ?

Thank you for the suggestion. You're right, it makes sense to return true in this case.
I'll update the patch accordingly. Appreciate your feedback!                           
                                                                                      
>
>> +	}
>> +
>>  	if (unlikely((unsigned long)page->mapping |
>>  			page_ref_count(page) |
>>  #ifdef CONFIG_MEMCG
>> @@ -1586,29 +1593,16 @@ static __always_inline void page_del_and_expand(struct zone *zone,
>>  	account_freepages(zone, -nr_pages, migratetype);
>>  }
>>  
>> -static void check_new_page_bad(struct page *page)
>> -{
>> -	if (unlikely(PageHWPoison(page))) {
>> -		/* Don't complain about hwpoisoned pages */
>> -		if (PageBuddy(page))
>> -			__ClearPageBuddy(page);
>> -		return;
>> -	}
>> -
>> -	bad_page(page,
>> -		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
>> -}
>> -
>>  /*
>>   * This page is about to be returned from the page allocator
>>   */
>>  static bool check_new_page(struct page *page)
>>  {
>> -	if (likely(page_expected_state(page,
>> -				PAGE_FLAGS_CHECK_AT_PREP|__PG_HWPOISON)))
>> +	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_PREP)))
>>  		return false;
>>  
>> -	check_new_page_bad(page);
>> +	bad_page(page,
>> +		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
>>  	return true;
>>  }
>>