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

[Michael S. Tsirkin]

On Tue, May 12, 2026 at 11:56:02AM -0400, Gregory Price wrote:
> 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@xxxxxxxxxx>
> > 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

Does it matter? It makes my head hurt.

-- 
MST