linux-kernel - Re: [PATCH] mm/page_alloc: Consolidate unlikely handling in page_expected

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Message-ID: <b7347fad-9ea8-424b-b000-e3d01dfe0dd1@arm.com>
Date: Fri, 21 Mar 2025 11:10:23 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Ye Liu <ye.liu@...ux.dev>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Ye Liu <liuye@...inos.cn>
Subject: Re: [PATCH] mm/page_alloc: Consolidate unlikely handling in
 page_expected_state



On 3/21/25 06:43, Ye Liu wrote:
> From: Ye Liu <liuye@...inos.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@...inos.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;
>  }
>