[PATCH 08/12] mm: khugepaged: add a helper to get the minimal collapse order

[Baolin Wang]

shmem mTHP collapse will need to support order-1 collapse in the future,
so add a helper to retrieve the minimal collapse order as a preparation.
Also rename KHUGEPAGED_MIN_MTHP_ORDER to KHUGEPAGED_MIN_ANON_MTHP_ORDER
for better readability, and add a new COLLAPSE_MIN_FILE_MTHP_ORDER for
the shmem minimal collapse order.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/collapse.h   |  3 ++-
 mm/khugepaged.c | 10 +++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/collapse.h b/mm/collapse.h
index e52969965262..d2fff6b5e1ec 100644
--- a/mm/collapse.h
+++ b/mm/collapse.h
@@ -8,7 +8,8 @@
 #include <linux/types.h>
 
 #define COLLAPSE_MAX_PTES_LIMIT		(HPAGE_PMD_NR - 1)
-#define COLLAPSE_MIN_MTHP_ORDER		2
+#define COLLAPSE_MIN_ANON_MTHP_ORDER		2
+#define COLLAPSE_MIN_FILE_MTHP_ORDER		1
 
 enum scan_result {
 	SCAN_FAIL,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6c648ede24c4..64605a72ac2b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -302,6 +302,14 @@ static bool pte_none_or_zero(pte_t pte)
 	return pte_present(pte) && is_zero_pfn(pte_pfn(pte));
 }
 
+static unsigned int collapse_min_mthp_order(struct file *file)
+{
+	if (file)
+		return COLLAPSE_MIN_FILE_MTHP_ORDER;
+
+	return COLLAPSE_MIN_ANON_MTHP_ORDER;
+}
+
 /**
  * collapse_max_ptes_none - Calculate maximum allowed empty PTEs or PTEs mapping
  * the shared zeropage for the given collapse operation.
@@ -1485,7 +1493,7 @@ static enum scan_result mthp_collapse(struct mm_struct *mm, unsigned long addres
 		 * any smaller order enabled. When at the smallest order
 		 * we must always move to the next offset.
 		 */
-		if (order > COLLAPSE_MIN_MTHP_ORDER &&
+		if (order > collapse_min_mthp_order(NULL) &&
 		    (cc->scan_orders & GENMASK(order - 1, 0))) {
 			order--;
 			continue;
-- 
2.47.3