On Tue, Dec 23, 2025 at 5:45 AM Pratyush Yadav <[email protected]> wrote:
>
> When restoring a page (from kho_restore_pages()) or folio (from
> kho_restore_folio()), KHO must initialize the struct page. The
> initialization differs slightly depending on if a folio is requested or
> a set of 0-order pages is requested.
>
> Conceptually, it is quite simple to understand. When restoring 0-order
> pages, each page gets a refcount of 1 and that's it. When restoring a
> folio, head page gets a refcount of 1 and tail pages get 0.
>
> kho_restore_page() tries to combine the two separate initialization flow
> into one piece of code. While it works fine, it is more complicated to
> read than it needs to be. Make the code simpler by splitting the two
> initalization paths into two separate functions. This improves
> readability by clearly showing how each type must be initialized.
>
> Signed-off-by: Pratyush Yadav <[email protected]>
> ---
>
> Notes:
> This patch is a follow up from
> https://lore.kernel.org/linux-mm/[email protected]/
>
> kernel/liveupdate/kexec_handover.c | 41 ++++++++++++++++++++----------
> 1 file changed, 27 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index 2d9ce33c63dc..304c26fd5ee6 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -219,11 +219,33 @@ static int __kho_preserve_order(struct kho_mem_track
> *track, unsigned long pfn,
> return 0;
> }
>
> +/* For physically contiguous 0-order pages. */
> +static void kho_init_pages(struct page *page, unsigned int nr_pages)
Here and in other places below, it is better for nr_pages to be
unsigned long. This is consistent with other places in mm, where we
have gradually moved on from int/unsigned int to unsigned long for
npages (see gup.c for example). Otherwise, LGTM.
> +{
> + 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);
> +}
> +
> static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
> {
> struct page *page = pfn_to_online_page(PHYS_PFN(phys));
> - unsigned int nr_pages, ref_cnt;
> union kho_page_info info;
> + unsigned int nr_pages;
>
> if (!page)
> return NULL;
> @@ -240,20 +262,11 @@ static struct page *kho_restore_page(phys_addr_t phys,
> bool is_folio)
>
> /* Clear private to make sure later restores on this page error out.
> */
> page->private = 0;
> - /* Head page gets refcount of 1. */
> - set_page_count(page, 1);
>
> - /*
> - * 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, ref_cnt);
> -
> - if (is_folio && info.order)
> - prep_compound_page(page, info.order);
> + if (is_folio)
> + kho_init_folio(page, info.order);
> + else
> + kho_init_pages(page, nr_pages);
Thanks,
Pasha
