On 7/9/26 9:25 PM, Li Zhe wrote:
> memmap_init_zone_device() currently mixes refcount policy and core
> ZONE_DEVICE page setup in a single helper.
>
> Factor the refcount-reset predicate into pagemap_resets_refcount(), move
> the common page initialization into __zone_device_page_init(), and wrap
> the existing slow path in zone_device_page_init_slow().
>
> This keeps the slow-path behaviour unchanged and gives later patches
> reusable helper boundaries.
>
> No functional change intended.
>
> Signed-off-by: Li Zhe <[email protected]>
> Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
> ---
> mm/mm_init.c | 56 ++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 37 insertions(+), 19 deletions(-)
>
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 95808ab5cfdb..5fccfbacf855 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1005,11 +1005,37 @@ static void __init memmap_init(void)
> }
>
> #ifdef CONFIG_ZONE_DEVICE
> -static void __ref __init_zone_device_page(struct page *page, unsigned long
> pfn,
> +/*
> + * Return true when the free path for this pagemap type restores the page
> + * refcount to 1, so memmap_init_zone_device() can keep the count set by
> + * __init_single_page(). Otherwise initialize the refcount to 0 and leave
> + * it to the allocator or pgmap callbacks to raise it when the page is
> + * handed out again.
> + */
> +static inline bool pagemap_resets_refcount(const struct dev_pagemap *pgmap)
> +{
resets_refcount reads like it resets it to 0, but it could be just me. How does
pagemap_requires_refcount_reset() sound, with the value returned being toggled
> + /*
> + * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free
> + * path. The remaining ZONE_DEVICE types start from 0 here and raise
> + * the count again when the allocator or driver hands the page out.
> + */
> + switch (pgmap->type) {
> + case MEMORY_DEVICE_FS_DAX:
> + case MEMORY_DEVICE_PRIVATE:
> + case MEMORY_DEVICE_COHERENT:
> + case MEMORY_DEVICE_PCI_P2PDMA:
> + return false;
> + case MEMORY_DEVICE_GENERIC:
> + return true;
> + }
> +
> + return true;
Shouldn't the default be a VM_WARN_ON()?
> +}
> +
> +static void __ref __zone_device_page_init(struct page *page, unsigned long
> pfn,
> unsigned long zone_idx, int nid,
> struct dev_pagemap *pgmap)
> {
> -
> __init_single_page(page, pfn, zone_idx, nid);
>
> /*
> @@ -1028,23 +1054,15 @@ static void __ref __init_zone_device_page(struct page
> *page, unsigned long pfn,
> */
> page_folio(page)->pgmap = pgmap;
> page->zone_device_data = NULL;
> +}
>
> - /*
> - * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free
> - * path. The remaining ZONE_DEVICE types start from 0 here and raise
> - * the count again when the allocator or driver hands the page out.
> - */
> - switch (pgmap->type) {
> - case MEMORY_DEVICE_FS_DAX:
> - case MEMORY_DEVICE_PRIVATE:
> - case MEMORY_DEVICE_COHERENT:
> - case MEMORY_DEVICE_PCI_P2PDMA:
> +static void __ref zone_device_page_init_slow(struct page *page,
> + unsigned long pfn, unsigned long zone_idx, int nid,
> + struct dev_pagemap *pgmap)
> +{
> + __zone_device_page_init(page, pfn, zone_idx, nid, pgmap);
> + if (!pagemap_resets_refcount(pgmap))
> set_page_count(page, 0);
> - break;
> -
> - case MEMORY_DEVICE_GENERIC:
> - break;
> - }
> }
>
> /*
> @@ -1090,7 +1108,7 @@ static void __ref memmap_init_compound(struct page
> *head,
> for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) {
> struct page *page = pfn_to_page(pfn);
>
> - __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
> + zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
> prep_compound_tail(page, head, order);
> set_page_count(page, 0);
> }
> @@ -1126,7 +1144,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
> for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) {
> struct page *page = pfn_to_page(pfn);
>
> - __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
> + zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
>
> if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
> cond_resched();
Balbir
