Re: [RFC PATCH 08/26] hugetlb: add hugetlb_free_range to free PT structures

["manish.mishra" <manish.mishra@nutanix.com>]

On 24/06/22 11:06 pm, James Houghton wrote:
> This is a helper function for freeing the bits of the page table that
> map a particular HugeTLB PTE.
>
> Signed-off-by: James Houghton <jthoughton@google.com>
> ---
>   include/linux/hugetlb.h |  2 ++
>   mm/hugetlb.c            | 17 +++++++++++++++++
>   2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 1d4ec9dfdebf..33ba48fac551 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -107,6 +107,8 @@ bool hugetlb_pte_none_mostly(const struct hugetlb_pte *hpte);
>   pte_t hugetlb_ptep_get(const struct hugetlb_pte *hpte);
>   void hugetlb_pte_clear(struct mm_struct *mm, const struct hugetlb_pte *hpte,
>   		       unsigned long address);
> +void hugetlb_free_range(struct mmu_gather *tlb, const struct hugetlb_pte *hpte,
> +			unsigned long start, unsigned long end);
>   
>   struct hugepage_subpool {
>   	spinlock_t lock;
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1a1434e29740..a2d2ffa76173 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1120,6 +1120,23 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
>   	return false;
>   }
>   
> +void hugetlb_free_range(struct mmu_gather *tlb, const struct hugetlb_pte *hpte,
> +			unsigned long start, unsigned long end)
> +{
> +	unsigned long floor = start & hugetlb_pte_mask(hpte);
> +	unsigned long ceiling = floor + hugetlb_pte_size(hpte);
> +
> +	if (hugetlb_pte_size(hpte) >= PGDIR_SIZE) {

sorry again did not understand why it is >= check and not just ==, does it help

in non-x86 arches.

> +		free_p4d_range(tlb, (pgd_t *)hpte->ptep, start, end, floor, ceiling);
> +	} else if (hugetlb_pte_size(hpte) >= P4D_SIZE) {
> +		free_pud_range(tlb, (p4d_t *)hpte->ptep, start, end, floor, ceiling);
> +	} else if (hugetlb_pte_size(hpte) >= PUD_SIZE) {
> +		free_pmd_range(tlb, (pud_t *)hpte->ptep, start, end, floor, ceiling);
> +	} else if (hugetlb_pte_size(hpte) >= PMD_SIZE) {
> +		free_pte_range(tlb, (pmd_t *)hpte->ptep, start);
> +	}
> +}
> +
>   bool hugetlb_pte_present_leaf(const struct hugetlb_pte *hpte)
>   {
>   	pgd_t pgd;