Re: [PATCH v10 03/13] khugepaged: generalize hugepage_vma_revalidate for mTHP support

On Sat, Aug 23, 2025 at 7:37 PM Wei Yang [off-list ref] wrote:

Hi, Nico

Some nit below.

On Tue, Aug 19, 2025 at 07:41:55AM -0600, Nico Pache wrote:

quoted

For khugepaged to support different mTHP orders, we must generalize this
to check if the PMD is not shared by another VMA and the order is enabled.

To ensure madvise_collapse can support working on mTHP orders without the
PMD order enabled, we need to convert hugepage_vma_revalidate to take a
bitmap of orders.

No functional change in this patch.

Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <redacted>
Co-developed-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Nico Pache <redacted>
---
mm/khugepaged.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b7b98aebb670..2d192ec961d2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c

There is a comment above this function, which says "revalidate vma before
taking mmap_lock".

I am afraid it is "after taking mmap_lock"? or "after taking mmap_lock again"?

Good catch, never noticed that. I updated the comment!

quoted

@@ -917,7 +917,7 @@ static int collapse_find_target_node(struct collapse_control *cc)

static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
                                 bool expect_anon,
                                 struct vm_area_struct **vmap,
-                                 struct collapse_control *cc)
+                                 struct collapse_control *cc, unsigned long orders)
{
      struct vm_area_struct *vma;
      enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :

@@ -930,9 +930,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
      if (!vma)
              return SCAN_VMA_NULL;

+      /* Always check the PMD order to insure its not shared by another VMA */
      if (!thp_vma_suitable_order(vma, address, PMD_ORDER))
              return SCAN_ADDRESS_RANGE;
-      if (!thp_vma_allowable_order(vma, vma->vm_flags, type, PMD_ORDER))
+      if (!thp_vma_allowable_orders(vma, vma->vm_flags, type, orders))
              return SCAN_VMA_CHECK;
      /*
       * Anon VMA expected, the address may be unmapped then

Below is a comment, "thp_vma_allowable_order may return".

Since you use thp_vma_allowable_orders, maybe we need to change the comment
too.

Ack! Thanks for the review!

quoted

@@ -1134,7 +1135,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
              goto out_nolock;

      mmap_read_lock(mm);
-      result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
+      result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
+                                       BIT(HPAGE_PMD_ORDER));
      if (result != SCAN_SUCCEED) {
              mmap_read_unlock(mm);
              goto out_nolock;

@@ -1168,7 +1170,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
       * mmap_lock.
       */
      mmap_write_lock(mm);
-      result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
+      result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
+                                       BIT(HPAGE_PMD_ORDER));
      if (result != SCAN_SUCCEED)
              goto out_up_write;
      /* check if the pmd is still valid */

@@ -2807,7 +2810,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
                      mmap_read_lock(mm);
                      mmap_locked = true;
                      result = hugepage_vma_revalidate(mm, addr, false, &vma,
-                                                       cc);
+                                                       cc, BIT(HPAGE_PMD_ORDER));
                      if (result  != SCAN_SUCCEED) {
                              last_fail = result;
                              goto out_nolock;
--

2.50.1

--
Wei Yang
Help you, Help me