[PATCH v2 2/5] mm/mm_init: remove redundant clamping in zone_spanned_pages_in_node()

[Sang-Heon Jeon <ekffu200098@gmail.com>]

Clamping *zone_end_pfn to node_end_pfn has no effect, because
*zone_end_pfn <= node_end_pfn is guaranteed at that point.

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

2. Else If zone_movable_pfn[nid] != 0 &&
   *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.

   So zone_movable_pfn[nid] < clamped *zone_end_pfn =
   min(node_end_pfn, zone_high) <= node_end_pfn.

3. Else *zone_end_pfn = clamp(node_end_pfn, zone_low, zone_high)

   a. If node_end_pfn >= zone_low, *zone_end_pfn =
      min(node_end_pfn, zone_high) <= node_end_pfn.

   b. If node_end_pfn < zone_low, *zone_start_pfn = zone_low >
      node_end_pfn, so the function returns 0 before the clamping is
      executed.

So remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
 mm/mm_init.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 30d3125951f0..bdc15de0a62a 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1219,8 +1219,7 @@ static unsigned long __init zone_spanned_pages_in_node(int nid,
 	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_end_pfn = min(*zone_end_pfn, node_end_pfn);
+	/* Move the zone start inside the node if necessary */
 	*zone_start_pfn = max(*zone_start_pfn, node_start_pfn);
 
 	/* Return the spanned pages */
-- 
2.43.0