mm/mlock: implement folio_mlock_step() using folio_pte_batch()

Let's make folio_mlock_step() simply a wrapper around folio_pte_batch(),
which will greatly reduce the cost of ptep_get() when scanning a range of
contptes.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Lance Yang <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Suggested-by: Barry Song <[email protected]>
Suggested-by: Matthew Wilcox <[email protected]>
Cc: Bang Li <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Yin Fengwei <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ioworker0

mm/mlock.c

@@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
 static inline unsigned int folio_mlock_step(struct folio *folio,
 		pte_t *pte, unsigned long addr, unsigned long end)
 {
-	unsigned int count, i, nr = folio_nr_pages(folio);
-	unsigned long pfn = folio_pfn(folio);
+	const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
+	unsigned int count = (end - addr) >> PAGE_SHIFT;
 	pte_t ptent = ptep_get(pte);
 
 	if (!folio_test_large(folio))
 		return 1;
 
-	count = pfn + nr - pte_pfn(ptent);
-	count = min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
-
-	for (i = 0; i < count; i++, pte++) {
-		pte_t entry = ptep_get(pte);
-
-		if (!pte_present(entry))
-			break;
-		if (pte_pfn(entry) - pfn >= nr)
-			break;
-	}
-
-	return i;
+	return folio_pte_batch(folio, addr, pte, ptent, count, fpb_flags, NULL,
+			       NULL, NULL);
 }
 
 static inline bool allow_mlock_munlock(struct folio *folio,