Re: [PATCH resend v6 20/30] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero

[Gregory Price <gourry@gourry.net>]

On Mon, May 11, 2026 at 05:03:35AM -0400, Michael S. Tsirkin wrote:
> When two buddy pages merge in __free_one_page(), preserve
> PG_zeroed on the merged page only if both buddies have the
> flag set.  Otherwise clear it.
> 
> The merged page would inherit PG_zeroed, and a later __GFP_ZERO
> allocation would skip zeroing stale data in the non-zero half.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: Claude:claude-opus-4-6
> Assisted-by: cursor-agent:GPT-5.4-xhigh
> ---
>  mm/page_alloc.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bd3b909cacdf..d70c9ba6b329 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -940,10 +940,14 @@ static inline void __free_one_page(struct page *page,
>  	unsigned long buddy_pfn = 0;
>  	unsigned long combined_pfn;
>  	struct page *buddy;
> +	bool buddy_zeroed;
> +	bool page_zeroed;

If you want to play some code golf, i think you can get away with a
single bool here:

    bool zeroed;
    zeroed = PageZeroed(buddy);
    zeroed &= PageZeroed(page);

    if (zeroed)
        __SetPageZeroed(page);

~Gregory