[RFC PATCH 05/12] khugepaged: Generalize __collapse_huge_page_isolate()

[Dev Jain <dev.jain@arm.com>]

Scale down the scan range and the sysfs tunables according to the scan order,
and isolate the folios.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
 mm/khugepaged.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f52dae7d5179..de044b1f83d4 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -564,15 +564,18 @@ 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, int order)
 {
-	struct page *page = NULL;
-	struct folio *folio = NULL;
-	pte_t *_pte;
+	unsigned int max_ptes_shared = khugepaged_max_ptes_shared >> (HPAGE_PMD_ORDER - order);
+	unsigned int max_ptes_none = khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - order);
 	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
+	struct folio *folio = NULL;
+	struct page *page = NULL;
 	bool writable = false;
+	pte_t *_pte;
 
-	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
+
+	for (_pte = pte; _pte < pte + (1UL << order);
 	     _pte++, address += PAGE_SIZE) {
 		pte_t pteval = ptep_get(_pte);
 		if (pte_none(pteval) || (pte_present(pteval) &&
@@ -580,7 +583,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 			++none_or_zero;
 			if (!userfaultfd_armed(vma) &&
 			    (!cc->is_khugepaged ||
-			     none_or_zero <= khugepaged_max_ptes_none)) {
+			     none_or_zero <= max_ptes_none)) {
 				continue;
 			} else {
 				result = SCAN_EXCEED_NONE_PTE;
@@ -609,7 +612,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		if (folio_likely_mapped_shared(folio)) {
 			++shared;
 			if (cc->is_khugepaged &&
-			    shared > khugepaged_max_ptes_shared) {
+			    shared > max_ptes_shared) {
 				result = SCAN_EXCEED_SHARED_PTE;
 				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
 				goto out;
@@ -1200,7 +1203,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl);
 	if (pte) {
 		result = __collapse_huge_page_isolate(vma, address, pte, cc,
-						      &compound_pagelist);
+						      &compound_pagelist, order);
 		spin_unlock(pte_ptl);
 	} else {
 		result = SCAN_PMD_NULL;
-- 
2.30.2