Re: [PATCH 2/2] kho: fix restoring of contiguous ranges of order-0 pages

Mike Rapoport
2025-12-01T06:54:56Z

Hi Pratyush,

On Tue, Nov 25, 2025 at 02:45:59PM +0100, Pratyush Yadav wrote:
> On Tue, Nov 25 2025, Mike Rapoport wrote:

...

> > @@ -243,11 +243,16 @@ static struct page *kho_restore_page(phys_addr_t phys)
> > /* Head page gets refcount of 1. */
> > set_page_count(page, 1);
> >
> > - /* For higher order folios, tail pages get a page count of zero. */
> > + /*
> > + * For higher order folios, tail pages get a page count of zero.
> > + * For physically contiguous order-0 pages every pages gets a page
> > + * count of 1
> > + */
> > + ref_cnt = is_folio ? 0 : 1;
> > for (unsigned int i = 1; i < nr_pages; i++)
> > - set_page_count(page + i, 0);
> > + set_page_count(page + i, ref_cnt);
> >
> > - if (info.order > 0)
> > + if (is_folio && info.order)
>
> This is getting a bit difficult to parse. Let's separate out folio and
> page initialization to separate helpers:

Sorry, I've missed this earlier and now the patches are in akpm's -stable
branch.
Let's postpone these changes for the next cycle, maybe along with support
for deferred initialization of struct page.

> /* Initalize 0-order KHO pages */
> static void kho_init_page(struct page *page, unsigned int nr_pages)
> {
> for (unsigned int i = 0; i < nr_pages; i++)
> set_page_count(page + i, 1);
> }
>
> static void kho_init_folio(struct page *page, unsigned int order)
> {
> unsigned int nr_pages = (1 << order);
>
> /* Head page gets refcount of 1. */
> set_page_count(page, 1);
>
> /* For higher order folios, tail pages get a page count of zero. */
> for (unsigned int i = 1; i < nr_pages; i++)
> set_page_count(page + i, 0);
>
> if (order > 0)
> prep_compound_page(page, order);
> }

--
Sincerely yours,
Mike.