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

Nico Pache
2025-10-22T18:40:18Z

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