[PATCH mm-unstable v19 10/14] mm/khugepaged: introduce collapse_possible_orders helper functions

[Nico Pache]

Add collapse_possible_orders() to generalize THP order eligibility. The
function determines which THP orders are permitted based on collapse
context (khugepaged vs madv_collapse). We also add collapse_possible()
as a thin wrapper around collapse_possible_orders() that returns a bool
rather than the whole bitmap.

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

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
---
 mm/khugepaged.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 26c343a6fa3d..ec886a031952 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -554,12 +554,30 @@ void __khugepaged_enter(struct mm_struct *mm)
 		wake_up_interruptible(&khugepaged_wait);
 }
 
+/*
+ * Check what orders are possible based on the vma and collapse type.
+ * This is used to determine if mTHP collapse is a viable option.
+ */
+static unsigned long collapse_possible_orders(struct vm_area_struct *vma,
+		vm_flags_t vm_flags, enum tva_type tva_flags)
+{
+	const unsigned long orders = BIT(HPAGE_PMD_ORDER);
+
+	return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
+}
+
+static bool collapse_possible(struct vm_area_struct *vma,
+		vm_flags_t vm_flags, enum tva_type tva_flags)
+{
+	return collapse_possible_orders(vma, vm_flags, tva_flags);
+}
+
 void khugepaged_enter_vma(struct vm_area_struct *vma,
 			  vm_flags_t vm_flags)
 {
 	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_possible(vma, vm_flags, TVA_KHUGEPAGED))
 			__khugepaged_enter(vma->vm_mm);
 	}
 }
@@ -2700,7 +2718,7 @@ static void collapse_scan_mm_slot(unsigned int progress_max,
 			cc->progress++;
 			break;
 		}
-		if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
+		if (!collapse_possible(vma, vma->vm_flags, TVA_KHUGEPAGED)) {
 			cc->progress++;
 			continue;
 		}
@@ -3010,7 +3028,7 @@ 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_possible(vma, vma->vm_flags, TVA_FORCED_COLLAPSE))
 		return -EINVAL;
 
 	cc = kmalloc_obj(*cc);
-- 
2.54.0