Subject: Re: [PATCH v3 15/19] mm/hugetlb_vmemmap: Move bootmem HVO setup to early init

From: Usama Arif <[email-masked]>
Date: Wed, 3 Jun 2026 05:02:44 -0700

On Tue,  2 Jun 2026 18:10:35 +0800 Muchun Song <[email-masked]> wrote:

> Bootmem HugeTLB pages currently defer HVO setup to
> hugetlb_vmemmap_init_late(), because the optimization needs zone
> information.
> 
> Now that zone initialization is available earlier, the bootmem HVO setup
> can be done directly from hugetlb_vmemmap_init_early(). This lets
> gigantic HugeTLB pages apply HVO as soon as they are allocated.
> 
> Bootmem gigantic pages that span multiple zones are now filtered out
> when they are allocated, so the remaining bootmem gigantic pages seen by
> later hugetlb initialization are already zone-valid. As a result,
> hugetlb_vmemmap_init_late() no longer needs to handle bootmem HVO setup.
> 
> Signed-off-by: Muchun Song <[email-masked]>
> ---
>  mm/hugetlb_vmemmap.c | 67 +++++++++-----------------------------------
>  1 file changed, 13 insertions(+), 54 deletions(-)
> 
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index ea6af85bfec1..464578ee246e 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -745,6 +745,8 @@ static bool vmemmap_should_optimize_bootmem_page(struct huge_bootmem_page *m)
>  	return true;
>  }
>  
> +static struct zone *pfn_to_zone(unsigned nid, unsigned long pfn);
> +
>  /*
>   * Initialize memmap section for a gigantic page, HVO-style.
>   */
> @@ -752,6 +754,7 @@ void __init hugetlb_vmemmap_init_early(int nid)
>  {
>  	unsigned long psize, paddr, section_size;
>  	unsigned long ns, i, pnum, pfn, nr_pages;
> +	unsigned long start, end;
>  	struct huge_bootmem_page *m = NULL;
>  	void *map;
>  
> @@ -761,6 +764,8 @@ void __init hugetlb_vmemmap_init_early(int nid)
>  	section_size = (1UL << PA_SECTION_SHIFT);
>  
>  	list_for_each_entry(m, &huge_boot_pages[nid], list) {
> +		struct zone *zone;
> +
>  		if (!vmemmap_should_optimize_bootmem_page(m))
>  			continue;
>  
> @@ -769,6 +774,14 @@ void __init hugetlb_vmemmap_init_early(int nid)
>  		paddr = virt_to_phys(m);
>  		pfn = PHYS_PFN(paddr);
>  		map = pfn_to_page(pfn);
> +		start = (unsigned long)map;
> +		end = start + hugetlb_vmemmap_size(m->hstate);
> +		zone = pfn_to_zone(nid, pfn);
> +
> +		if (vmemmap_populate_hvo(start, end, huge_page_order(m->hstate),
> +					 zone, HUGETLB_VMEMMAP_RESERVE_SIZE))
> +			panic("Failed to allocate memmap for HugeTLB page\n");

The replaced hugetlb_vmemmap_init_late() path used to fall back to
vmemmap_populate() if vmemmap_populate_hvo() returned an error and
just lost the HVO optimization for that page.

The new path panics on any non-zero return.  Is the panic intended,
given that vmemmap_populate_hvo() returns -ENOMEM on allocation
failure and HVO is normally treated as an optimization rather than a
hard requirement?

> +		memmap_boot_pages_add(DIV_ROUND_UP(HUGETLB_VMEMMAP_RESERVE_SIZE, PAGE_SIZE));
>  
>  		pnum = pfn_to_section_nr(pfn);
>  		ns = psize / section_size;
> @@ -800,60 +813,6 @@ static struct zone *pfn_to_zone(unsigned nid, unsigned long pfn)
>  
>  void __init hugetlb_vmemmap_init_late(int nid)
>  {
> -	struct huge_bootmem_page *m, *tm;
> -	unsigned long phys, nr_pages, start, end;
> -	unsigned long pfn, nr_mmap;
> -	struct zone *zone = NULL;
> -	struct hstate *h;
> -	void *map;
> -
> -	if (!READ_ONCE(vmemmap_optimize_enabled))
> -		return;
> -
> -	list_for_each_entry_safe(m, tm, &huge_boot_pages[nid], list) {
> -		if (!(m->flags & HUGE_BOOTMEM_HVO))
> -			continue;
> -
> -		phys = virt_to_phys(m);
> -		h = m->hstate;
> -		pfn = PHYS_PFN(phys);
> -		nr_pages = pages_per_huge_page(h);
> -		map = pfn_to_page(pfn);
> -		start = (unsigned long)map;
> -		end = start + nr_pages * sizeof(struct page);
> -
> -		if (!hugetlb_bootmem_page_zones_valid(nid, m)) {
> -			/*
> -			 * Oops, the hugetlb page spans multiple zones.
> -			 * Remove it from the list, and populate it normally.
> -			 */
> -			list_del(&m->list);
> -
> -			vmemmap_populate(start, end, nid, NULL);
> -			nr_mmap = end - start;
> -			memmap_boot_pages_add(DIV_ROUND_UP(nr_mmap, PAGE_SIZE));
> -
> -			memblock_phys_free(phys, huge_page_size(h));
> -			continue;
> -		}
> -
> -		if (!zone || !zone_spans_pfn(zone, pfn))
> -			zone = pfn_to_zone(nid, pfn);
> -		if (WARN_ON_ONCE(!zone))
> -			continue;
> -
> -		if (vmemmap_populate_hvo(start, end, huge_page_order(h), zone,
> -					 HUGETLB_VMEMMAP_RESERVE_SIZE) < 0) {
> -			/* Fallback if HVO population fails */
> -			vmemmap_populate(start, end, nid, NULL);
> -			nr_mmap = end - start;
> -		} else {
> -			m->flags |= HUGE_BOOTMEM_ZONES_VALID;
> -			nr_mmap = HUGETLB_VMEMMAP_RESERVE_SIZE;
> -		}
> -
> -		memmap_boot_pages_add(DIV_ROUND_UP(nr_mmap, PAGE_SIZE));
> -	}
>  }
>  #endif
>  
> -- 
> 2.54.0
> 
>