Re: [PATCH resend v6 21/30] mm: page_alloc: preserve PG_zeroed in page_del_and_expand

[Gregory Price <gourry@gourry.net>]

On Mon, May 11, 2026 at 05:03:41AM -0400, Michael S. Tsirkin wrote:
> Propagate PG_zeroed through buddy splits in page_del_and_expand()
> and try_to_claim_block().  When a zeroed high-order page is split
> to satisfy a smaller allocation, the sub-pages placed back on the
> free lists keep PG_zeroed.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: Claude:claude-opus-4-6
> Assisted-by: cursor-agent:GPT-5.4-xhigh

Reviewed-by: Gregory Price <gourry@gourry.net>

> ---
>  mm/page_alloc.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d70c9ba6b329..468e8bde7d34 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1712,7 +1712,8 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>   * -- nyc
>   */
>  static inline unsigned int expand(struct zone *zone, struct page *page, int low,
> -				  int high, int migratetype, bool reported)
> +				  int high, int migratetype, bool reported,
> +				  bool zeroed)
>  {
>  	unsigned int size = 1 << high;
>  	unsigned int nr_added = 0;
> @@ -1743,6 +1744,8 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low,
>  		 */
>  		if (reported)
>  			__SetPageReported(&page[size]);
> +		if (zeroed)
> +			__SetPageZeroed(&page[size]);
>  	}
>  
>  	return nr_added;
> @@ -1754,10 +1757,12 @@ static __always_inline void page_del_and_expand(struct zone *zone,
>  {
>  	int nr_pages = 1 << high;
>  	bool was_reported = page_reported(page);
> +	bool was_zeroed = PageZeroed(page);
>  
>  	__del_page_from_free_list(page, zone, high, migratetype);
>  
> -	nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
> +	nr_pages -= expand(zone, page, low, high, migratetype, was_reported,
> +			   was_zeroed);
>  	account_freepages(zone, -nr_pages, migratetype);
>  }
>  
> @@ -2335,11 +2340,12 @@ try_to_claim_block(struct zone *zone, struct page *page,
>  	if (current_order >= pageblock_order) {
>  		unsigned int nr_added;
>  		bool was_reported = page_reported(page);
> +		bool was_zeroed = PageZeroed(page);
>  
>  		del_page_from_free_list(page, zone, current_order, block_type);
>  		change_pageblock_range(page, current_order, start_type);
>  		nr_added = expand(zone, page, order, current_order, start_type,
> -				  was_reported);
> +				  was_reported, was_zeroed);
>  		account_freepages(zone, nr_added, start_type);
>  		return page;
>  	}
> -- 
> MST
>