Re: [RFC 07/11] khugepaged: generalize __collapse_huge_page_* for mTHP support

Dev Jain
2025-01-10T06:38:54Z

On 09/01/25 5:01 am, Nico Pache wrote:
> generalize the order of the __collapse_huge_page_* functions
> to support future mTHP collapse.
>
> No functional changes in this patch.
>
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
> mm/khugepaged.c | 36 +++++++++++++++++++-----------------
> 1 file changed, 19 insertions(+), 17 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 6daf3a943a1a..9eb161b04ee4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -565,7 +565,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> unsigned long address,
> pte_t *pte,
> struct collapse_control *cc,
> - struct list_head *compound_pagelist)
> + struct list_head *compound_pagelist,
> + u8 order)
> {
> struct page *page = NULL;
> struct folio *folio = NULL;
> @@ -573,7 +574,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
> bool writable = false;
>
> - for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> + for (_pte = pte; _pte < pte + (1 << order);
> _pte++, address += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> if (pte_none(pteval) || (pte_present(pteval) &&
> @@ -711,14 +712,15 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte,
> struct vm_area_struct *vma,
> unsigned long address,
> spinlock_t *ptl,
> - struct list_head *compound_pagelist)
> + struct list_head *compound_pagelist,
> + u8 order)
> {
> struct folio *src, *tmp;
> pte_t *_pte;
> pte_t pteval;
>
> - for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> - _pte++, address += PAGE_SIZE) {
> + for (_pte = pte; _pte < pte + (1 << order);
> + _pte++, address += PAGE_SIZE) {
> pteval = ptep_get(_pte);
> if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
> @@ -764,7 +766,8 @@ static void __collapse_huge_page_copy_failed(pte_t *pte,
> pmd_t *pmd,
> pmd_t orig_pmd,
> struct vm_area_struct *vma,
> - struct list_head *compound_pagelist)
> + struct list_head *compound_pagelist,
> + u8 order)
> {
> spinlock_t *pmd_ptl;
>
> @@ -781,7 +784,7 @@ static void __collapse_huge_page_copy_failed(pte_t *pte,
> * Release both raw and compound pages isolated
> * in __collapse_huge_page_isolate.
> */
> - release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist);
> + release_pte_pages(pte, pte + (1 << order), compound_pagelist);
> }
>
> /*
> @@ -802,7 +805,7 @@ static void __collapse_huge_page_copy_failed(pte_t *pte,
> static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
> pmd_t *pmd, pmd_t orig_pmd, struct vm_area_struct *vma,
> unsigned long address, spinlock_t *ptl,
> - struct list_head *compound_pagelist)
> + struct list_head *compound_pagelist, u8 order)
> {
> unsigned int i;
> int result = SCAN_SUCCEED;
> @@ -810,7 +813,7 @@ static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
> /*
> * Copying pages' contents is subject to memory poison at any iteration.
> */
> - for (i = 0; i < HPAGE_PMD_NR; i++) {
> + for (i = 0; i < (1 << order); i++) {
> pte_t pteval = ptep_get(pte + i);
> struct page *page = folio_page(folio, i);
> unsigned long src_addr = address + i * PAGE_SIZE;
> @@ -829,10 +832,10 @@ static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
>
> if (likely(result == SCAN_SUCCEED))
> __collapse_huge_page_copy_succeeded(pte, vma, address, ptl,
> - compound_pagelist);
> + compound_pagelist, order);
> else
> __collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma,
> - compound_pagelist);
> + compound_pagelist, order);
>
> return result;
> }
> @@ -996,11 +999,11 @@ static int check_pmd_still_valid(struct mm_struct *mm,
> static int __collapse_huge_page_swapin(struct mm_struct *mm,
> struct vm_area_struct *vma,
> unsigned long haddr, pmd_t *pmd,
> - int referenced)
> + int referenced, u8 order)
> {

I had dropped 'h' from haddr because the address won't be huge-aligned
after mTHP support.

> int swapped_in = 0;
> vm_fault_t ret = 0;
> - unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
> + unsigned long address, end = haddr + ((1 << order) * PAGE_SIZE);

Better to write PAGE_SIZE << order, as Matthew had noted in my patch :)