On 9/27/26 04:54, Muchun Song wrote:
> Device DAX still uses vmemmap_populate_compound_pages() to populate its
> compound-page vmemmap mappings. That helper allocates the head and first
> tail vmemmap pages explicitly, then reuses the first tail page for the
> remaining tail page mappings.
>
> Device DAX is being moved to the section-based vmemmap optimization
> infrastructure, but it cannot switch to the generic section-based
> population path yet. Once a later patch records the DAX compound page
> order in section metadata, DAX head and first-tail PFNs can look
> optimizable to the generic helpers as well.
>
> Add a DAX-specific population flag for this transition. It keeps DAX
Well, you're not adding flag, your reusing an existing one and renaming it?
And then you're specifying it on more paths.
[...]
> mm/sparse-vmemmap.c | 27 +++++++++++++++------------
> 1 file changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index e4dae98ba7f8..2457ea2c6dca 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -35,8 +35,8 @@
> /*
> * Flags for vmemmap_populate_range and friends.
> */
> -/* Get a ref on the head page struct page, for ZONE_DEVICE compound pages */
> -#define VMEMMAP_POPULATE_PAGEREF 0x0001
> +/* Vmemmap population for ZONE_DEVICE compound pages */
> +#define VMEMMAP_POPULATE_DAX 0x0001
Cleaner.
>
> #include "internal.h"
> #include "mm_init.h"
> @@ -243,13 +243,17 @@ static inline struct page
> *vmemmap_shared_tail_page(unsigned int order,
> #endif
>
> static __meminit void *vmemmap_alloc_pte(unsigned long pfn, int node,
> - struct vmem_altmap *altmap)
> + struct vmem_altmap *altmap, unsigned long flags)
> {
> struct zone *zone;
> struct page *page;
> const unsigned int order = pfn_to_section_compound_order(pfn);
>
> - if (!vmemmap_optimizable_pfn(pfn))
> + /*
> + * Device DAX still relies on vmemmap_populate_compound_pages() for
> + * head/first-tail allocation and tail-page reuse.
> + */
> + if (!vmemmap_optimizable_pfn(pfn) || flags & VMEMMAP_POPULATE_DAX)
> return vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
>
> zone = pfn_to_zone(pfn, node);
> @@ -271,7 +275,7 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd,
> unsigned long addr, in
> pte_t entry;
>
> if (ptpfn == (unsigned long)-1) {
> - void *p = vmemmap_alloc_pte(pfn, node, altmap);
> + void *p = vmemmap_alloc_pte(pfn, node, altmap, flags);
>
> if (!p)
> return NULL;
> @@ -286,7 +290,7 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd,
> unsigned long addr, in
> * and through vmemmap_populate_compound_pages() when
> * slab is available.
> */
> - if (flags & VMEMMAP_POPULATE_PAGEREF)
> + if (flags & VMEMMAP_POPULATE_DAX)
> get_page(pfn_to_page(ptpfn));
> }
> entry = pfn_pte(ptpfn, PAGE_KERNEL);
> @@ -546,6 +550,7 @@ static int __meminit
> vmemmap_populate_compound_pages(unsigned long start_pfn,
> unsigned long size, addr;
> pte_t *pte;
> int rc;
> + unsigned long flags = VMEMMAP_POPULATE_DAX;
const and at the top?
--
Cheers,
David
