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charset=UTF-8 Content-Transfer-Encoding: 7bit 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