[PATCH 3/4] mm/mm_init: move the range check and clamping inside ZONE_MOVABLE branch

[Sang-Heon Jeon]

Outside the ZONE_MOVABLE branch the check and the clamping have no
effect, because every branch ends with one of the following.

 - *zone_start_pfn == *zone_end_pfn, so the function returns 0 anyway.

 - node_start_pfn <= *zone_start_pfn <= *zone_end_pfn <= node_end_pfn,
   so the check does not return 0 and max(*zone_start_pfn,
   node_start_pfn) is always *zone_start_pfn.

The branches set *zone_start_pfn and *zone_end_pfn as follows.

1. If zone_movable_pfn[nid] != 0 && zone_type == ZONE_MOVABLE,
   *zone_start_pfn = zone_movable_pfn[nid] and *zone_end_pfn =
   min(node_end_pfn, ...).

2. Else If zone_movable_pfn[nid] != 0 && !mirrored_kernelcore &&
   *zone_start_pfn < zone_movable_pfn[nid] < *zone_end_pfn,
   *zone_end_pfn = zone_movable_pfn[nid].

   The condition requires the clamped *zone_start_pfn and
   *zone_end_pfn to differ, which cannot happen when node_end_pfn <
   zone_low or node_start_pfn > zone_high.

   So *zone_start_pfn = max(node_start_pfn, zone_low) >=
   node_start_pfn, and zone_movable_pfn[nid] < clamped *zone_end_pfn =
   min(node_end_pfn, zone_high) <= node_end_pfn.

   So node_start_pfn <= *zone_start_pfn < *zone_end_pfn <=
   node_end_pfn.

3. Else If zone_movable_pfn[nid] != 0 && *zone_start_pfn >=
   zone_movable_pfn[nid], *zone_start_pfn = *zone_end_pfn.

4. Else *zone_start_pfn = clamp(node_start_pfn, zone_low, zone_high)
   and *zone_end_pfn = clamp(node_end_pfn, zone_low, zone_high)

   a. If node_end_pfn < zone_low, *zone_start_pfn = *zone_end_pfn =
      zone_low.

   b. If node_start_pfn > zone_high, *zone_start_pfn = *zone_end_pfn =
      zone_high.

   c. If node_end_pfn >= zone_low && node_start_pfn <= zone_high,
      node_start_pfn <= *zone_start_pfn <= *zone_end_pfn <=
      node_end_pfn.

So move both inside the ZONE_MOVABLE branch.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@xxxxxxxxx>
---
 mm/mm_init.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 75fe1918d4d4..1190a27ed0fb 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1253,6 +1253,17 @@ static unsigned long __init zone_spanned_pages_in_node(int nid,
 			*zone_end_pfn = min(node_end_pfn,
 				arch_zone_highest_possible_pfn[movable_zone]);
 
+			/*
+			 * Check that this node has pages within the
+			 * zone's required range
+			 */
+			if (*zone_end_pfn < node_start_pfn ||
+			    *zone_start_pfn > node_end_pfn)
+				return 0;
+
+			/* Move the zone start inside the node if necessary */
+			*zone_start_pfn = max(*zone_start_pfn, node_start_pfn);
+
 		/* Adjust for ZONE_MOVABLE starting within this range */
 		} else if (!mirrored_kernelcore &&
 			*zone_start_pfn < zone_movable_pfn[nid] &&
@@ -1264,13 +1275,6 @@ static unsigned long __init zone_spanned_pages_in_node(int nid,
 			*zone_start_pfn = *zone_end_pfn;
 	}
 
-	/* Check that this node has pages within the zone's required range */
-	if (*zone_end_pfn < node_start_pfn || *zone_start_pfn > node_end_pfn)
-		return 0;
-
-	/* Move the zone boundaries inside the node if necessary */
-	*zone_start_pfn = max(*zone_start_pfn, node_start_pfn);
-
 	/* Return the spanned pages */
 	return *zone_end_pfn - *zone_start_pfn;
 }
-- 
2.43.0