Re: [PATCH v1 00/11] Zero page->private when freeing pages

[David Hildenbrand (Arm)]

On 2/23/26 15:06, Christian König wrote:
> On 2/23/26 14:46, Christoph Hellwig wrote:
> > On Sun, Feb 22, 2026 at 10:26:30PM -0500, Zi Yan wrote:
> > > Hi all,
> > >
> > > Based on a recent discussion with David Hildenbrand on page->private
> > > is not zero when a page is freed[1], this patchset is trying to fix all
> > > users do not zero ->private when freeing a page and add checks to make
> > > sure all freed pages have ->private set to zero. For compound pages,
> > > both head page and tail pages need to have ->private set to zero.
> >
> > Requiring the user to clear a field before freeing is just a way to
> > awkward interface.  Don't do that.
>
> Completely agree. This is just asking for trouble.
>
> The cache line(s) backing this struct page are most likely accessed anyway on free/alloc. So I don't see much extra overhead.

I think the question is more around handling non-head pages when freeing 
larger orders. But maybe the overhead of zeroing page->private it there 
as well in __free_pages_prepare() is tolerable.

I'll note, though, that we already require page->mapping and 
page->memcg_data of pages to be zeroed by the caller, so it's not 
completely crazy. (see page_expected_state)

--
Cheers,

David