[RFC Patch 07/11] mm/huge_memory: separate uniform/non uniform split logic in __split_unmapped_folio()

[Wei Yang <richard.weiyang@gmail.com>]

By utilizing the newly introduced __split_folio_and_update_stats()
helper function, we can now clearly separate the logic for uniform and
non-uniform folio splitting within __split_unmapped_folio().

This refactoring greatly simplifies the code by creating two distinct
execution paths:

    * Uniform Split: Directly calls __split_folio_and_update_stats()
      once to achieve the @new_order in a single operation.

    * Non-Uniform Split: Continues to use a loop to iteratively split
      the folio to a single lower order at a time, eventually reaching
      the @new_order.

This separation improves code clarity and maintainability.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: "David Hildenbrand (Red Hat)" <david@kernel.org>
---
 mm/huge_memory.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7160254ce76c..dbb4b86e7d6d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3634,14 +3634,20 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 {
 	const bool is_anon = folio_test_anon(folio);
 	int old_order = folio_order(folio);
-	int start_order = split_type == SPLIT_TYPE_UNIFORM ? new_order : old_order - 1;
 	int split_order;
 
+	/* For uniform split, folio is split to new_order directly. */
+	if (split_type == SPLIT_TYPE_UNIFORM) {
+		if (mapping)
+			xas_split(xas, folio, old_order);
+		__split_folio_and_update_stats(folio, old_order, new_order);
+		return 0;
+	}
+
 	/*
-	 * split to new_order one order at a time. For uniform split,
-	 * folio is split to new_order directly.
+	 * For non-uniform, split to new_order one order at a time.
 	 */
-	for (split_order = start_order;
+	for (split_order = old_order - 1;
 	     split_order >= new_order;
 	     split_order--) {
 		/* order-1 anonymous folio is not supported */
@@ -3654,21 +3660,16 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 			 * irq is disabled to allocate enough memory, whereas
 			 * non-uniform split can handle ENOMEM.
 			 */
-			if (split_type == SPLIT_TYPE_UNIFORM)
-				xas_split(xas, folio, old_order);
-			else {
-				xas_set_order(xas, folio->index, split_order);
-				xas_try_split(xas, folio, old_order);
-				if (xas_error(xas))
-					return xas_error(xas);
-			}
+			xas_set_order(xas, folio->index, split_order);
+			xas_try_split(xas, folio, old_order);
+			if (xas_error(xas))
+				return xas_error(xas);
 		}
 
 		__split_folio_and_update_stats(folio, old_order, split_order);
 		/*
-		 * If uniform split, the process is complete.
-		 * If non-uniform, continue splitting the folio at @split_at
-		 * as long as the next @split_order is >= @new_order.
+		 * Continue splitting the folio at @split_at as long as the
+		 * next @split_order is >= @new_order.
 		 */
 		folio = page_folio(split_at);
 		old_order = split_order;
-- 
2.34.1