[PATCH v12 mm-new 11/15] khugepaged: introduce collapse_allowable_orders helper function

[Nico Pache <npache@redhat.com>]

Add collapse_allowable_orders() to generalize THP order eligibility. The
function determines which THP orders are permitted based on collapse
context (khugepaged vs madv_collapse).

This consolidates collapse configuration logic and provides a clean
interface for future mTHP collapse support where the orders may be
different.

Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Nico Pache <npache@redhat.com>
---
 mm/khugepaged.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0dbbe04c31fe..89a105124790 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -489,7 +489,16 @@ static unsigned int collapse_max_ptes_none(unsigned int order, bool full_scan)
 	max_ptes_none = min(khugepaged_max_ptes_none, HPAGE_PMD_NR/2 - 1);
 
 	return max_ptes_none >> (HPAGE_PMD_ORDER - order);
+}
+
+/* Check what orders are allowed based on the vma and collapse type */
+static unsigned long collapse_allowable_orders(struct vm_area_struct *vma,
+			vm_flags_t vm_flags, bool is_khugepaged)
+{
+	enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE;
+	unsigned long orders = BIT(HPAGE_PMD_ORDER);
 
+	return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
 }
 
 void khugepaged_enter_vma(struct vm_area_struct *vma,
@@ -497,7 +506,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
 {
 	if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
 	    hugepage_pmd_enabled()) {
-		if (thp_vma_allowable_order(vma, vm_flags, TVA_KHUGEPAGED, PMD_ORDER))
+		if (collapse_allowable_orders(vma, vm_flags, true))
 			__khugepaged_enter(vma->vm_mm);
 	}
 }
@@ -2567,7 +2576,7 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, int *result,
 			progress++;
 			break;
 		}
-		if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
+		if (!collapse_allowable_orders(vma, vma->vm_flags, true)) {
 skip:
 			progress++;
 			continue;
@@ -2873,7 +2882,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 	BUG_ON(vma->vm_start > start);
 	BUG_ON(vma->vm_end < end);
 
-	if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
+	if (!collapse_allowable_orders(vma, vma->vm_flags, false))
 		return -EINVAL;
 
 	cc = kmalloc(sizeof(*cc), GFP_KERNEL);
-- 
2.51.0