mm/mempolicy: convert queue_pages_hugetlb() to queue_folios_hugetlb()

This change is in preparation for the conversion of queue_pages_required()
to queue_folio_required() and migrate_page_add() to migrate_folio_add().

Link: https://lkml.kernel.org/r/20230130201833.27042-5-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: "Yin, Fengwei" <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: VMoola

mm/mempolicy.c

@@ -558,29 +558,29 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
 	return addr != end ? -EIO : 0;
 }
 
-static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
+static int queue_folios_hugetlb(pte_t *pte, unsigned long hmask,
 			       unsigned long addr, unsigned long end,
 			       struct mm_walk *walk)
 {
 	int ret = 0;
 #ifdef CONFIG_HUGETLB_PAGE
 	struct queue_pages *qp = walk->private;
 	unsigned long flags = (qp->flags & MPOL_MF_VALID);
-	struct page *page;
+	struct folio *folio;
 	spinlock_t *ptl;
 	pte_t entry;
 
 	ptl = huge_pte_lock(hstate_vma(walk->vma), walk->mm, pte);
 	entry = huge_ptep_get(pte);
 	if (!pte_present(entry))
 		goto unlock;
-	page = pte_page(entry);
-	if (!queue_pages_required(page, qp))
+	folio = pfn_folio(pte_pfn(entry));
+	if (!queue_pages_required(&folio->page, qp))
 		goto unlock;
 
 	if (flags == MPOL_MF_STRICT) {
 		/*
-		 * STRICT alone means only detecting misplaced page and no
+		 * STRICT alone means only detecting misplaced folio and no
 		 * need to further check other vma.
 		 */
 		ret = -EIO;
@@ -591,21 +591,28 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
 		/*
 		 * Must be STRICT with MOVE*, otherwise .test_walk() have
 		 * stopped walking current vma.
-		 * Detecting misplaced page but allow migrating pages which
+		 * Detecting misplaced folio but allow migrating folios which
 		 * have been queued.
 		 */
 		ret = 1;
 		goto unlock;
 	}
 
-	/* With MPOL_MF_MOVE, we migrate only unshared hugepage. */
+	/*
+	 * With MPOL_MF_MOVE, we try to migrate only unshared folios. If it
+	 * is shared it is likely not worth migrating.
+	 *
+	 * To check if the folio is shared, ideally we want to make sure
+	 * every page is mapped to the same process. Doing that is very
+	 * expensive, so check the estimated mapcount of the folio instead.
+	 */
 	if (flags & (MPOL_MF_MOVE_ALL) ||
-	    (flags & MPOL_MF_MOVE && page_mapcount(page) == 1 &&
+	    (flags & MPOL_MF_MOVE && folio_estimated_sharers(folio) == 1 &&
 	     !hugetlb_pmd_shared(pte))) {
-		if (isolate_hugetlb(page_folio(page), qp->pagelist) &&
+		if (isolate_hugetlb(folio, qp->pagelist) &&
 			(flags & MPOL_MF_STRICT))
 			/*
-			 * Failed to isolate page but allow migrating pages
+			 * Failed to isolate folio but allow migrating pages
 			 * which have been queued.
 			 */
 			ret = 1;
@@ -703,7 +710,7 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
 }
 
 static const struct mm_walk_ops queue_pages_walk_ops = {
-	.hugetlb_entry		= queue_pages_hugetlb,
+	.hugetlb_entry		= queue_folios_hugetlb,
 	.pmd_entry		= queue_folios_pte_range,
 	.test_walk		= queue_pages_test_walk,
 };