[RFC PATCH 07/14] mm/khugepaged: add vm_flags_ignore to hugepage_vma_revalidate_pmd_count()

["Zach O'Keefe" <zokeefe@google.com>]

In madvise collapse context, we optionally want to be able to ignore
advice from MADV_NOHUGEPAGE-marked regions.

Add a vm_flags_ignore argument to hugepage_vma_revalidate_pmd_count()
which can be used to ignore vm flags used when considering thp
eligibility.

Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
 mm/khugepaged.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1d20be47bcea..ecbd3fc41c80 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -964,10 +964,14 @@ khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 #endif
 
 /*
- * Revalidate a vma's eligibility to collapse nr hugepages.
+ * Revalidate a vma's eligibility to collapse nr hugepages. vm_flags_ignore
+ * can be used to ignore certain vma_flags that would otherwise be checked -
+ * the principal example being VM_NOHUGEPAGE which is ignored in madvise
+ * collapse context.
  */
 static int hugepage_vma_revalidate_pmd_count(struct mm_struct *mm,
 					     unsigned long address, int nr,
+					     unsigned long vm_flags_ignore,
 					     struct vm_area_struct **vmap)
 {
 	struct vm_area_struct *vma;
@@ -986,7 +990,7 @@ static int hugepage_vma_revalidate_pmd_count(struct mm_struct *mm,
 	hend = vma->vm_end & HPAGE_PMD_MASK;
 	if (address < hstart || (address + nr * HPAGE_PMD_SIZE) > hend)
 		return SCAN_ADDRESS_RANGE;
-	if (!hugepage_vma_check(vma, vma->vm_flags))
+	if (!hugepage_vma_check(vma, vma->vm_flags & ~vm_flags_ignore))
 		return SCAN_VMA_CHECK;
 	/* Anon VMA expected */
 	if (!vma->anon_vma || vma->vm_ops)
@@ -1000,9 +1004,11 @@ static int hugepage_vma_revalidate_pmd_count(struct mm_struct *mm,
  */
 
 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
+				   unsigned long vm_flags_ignore,
 				   struct vm_area_struct **vmap)
 {
-	return hugepage_vma_revalidate_pmd_count(mm, address, 1, vmap);
+	return hugepage_vma_revalidate_pmd_count(mm, address, 1,
+			vm_flags_ignore, vmap);
 }
 
 /*
@@ -1043,7 +1049,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 		/* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
 		if (ret & VM_FAULT_RETRY) {
 			mmap_read_lock(mm);
-			if (hugepage_vma_revalidate(mm, haddr, &vma)) {
+			if (hugepage_vma_revalidate(mm, haddr, VM_NONE, &vma)) {
 				/* vma is no longer available, don't continue to swapin */
 				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 				return false;
@@ -1200,7 +1206,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
 
 	mmap_read_lock(mm);
-	result = hugepage_vma_revalidate(mm, address, &vma);
+	result = hugepage_vma_revalidate(mm, address, VM_NONE, &vma);
 	if (result) {
 		mmap_read_unlock(mm);
 		goto out_nolock;
@@ -1232,7 +1238,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 */
 	mmap_write_lock(mm);
 
-	result = hugepage_vma_revalidate(mm, address, &vma);
+	result = hugepage_vma_revalidate(mm, address, VM_NONE, &vma);
 	if (result)
 		goto out_up_write;
 	/* check if the pmd is still valid */
-- 
2.35.1.616.g0bdcbb4464-goog