[PATCH 2/5] mm/huge_memory: update folio stat after successful split

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

When a folio is successfully split, its statistics must be updated.

The current implementation complicates this process:

  * It iterates over the resulting new folios.
  * It uses a flag (@stop_split) to conditionally skip updating the stat
    for the folio at @split_at during the loop.
  * It then attempts to update the skipped stat on a subsequent failure
    path.

This logic is unnecessarily hard to follow.

This commit refactors the code to update the folio statistics only after
a successful split. This makes the logic much cleaner and sets the stage
for further simplification of the stat-handling code.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
---
 mm/huge_memory.c | 44 +++++++++++---------------------------------
 1 file changed, 11 insertions(+), 33 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4b2d5a7e5c8e..bafbd66769ac 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3530,13 +3530,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 	bool is_anon = folio_test_anon(folio);
 	int order = folio_order(folio);
 	int start_order = uniform_split ? new_order : order - 1;
-	bool stop_split = false;
 	struct folio *next;
 	int split_order;
-	int ret = 0;
-
-	if (is_anon)
-		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
 
 	folio_clear_has_hwpoisoned(folio);
 
@@ -3545,7 +3540,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 	 * folio is split to new_order directly.
 	 */
 	for (split_order = start_order;
-	     split_order >= new_order && !stop_split;
+	     split_order >= new_order;
 	     split_order--) {
 		struct folio *end_folio = folio_next(folio);
 		int old_order = folio_order(folio);
@@ -3568,49 +3563,32 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 			else {
 				xas_set_order(xas, folio->index, split_order);
 				xas_try_split(xas, folio, old_order);
-				if (xas_error(xas)) {
-					ret = xas_error(xas);
-					stop_split = true;
-				}
+				if (xas_error(xas))
+					return xas_error(xas);
 			}
 		}
 
-		if (!stop_split) {
-			folio_split_memcg_refs(folio, old_order, split_order);
-			split_page_owner(&folio->page, old_order, split_order);
-			pgalloc_tag_split(folio, old_order, split_order);
-
-			__split_folio_to_order(folio, old_order, split_order);
-		}
+		folio_split_memcg_refs(folio, old_order, split_order);
+		split_page_owner(&folio->page, old_order, split_order);
+		pgalloc_tag_split(folio, old_order, split_order);
+		__split_folio_to_order(folio, old_order, split_order);
 
+		if (is_anon)
+			mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1);
 		/*
 		 * Iterate through after-split folios and update folio stats.
-		 * But in buddy allocator like split, the folio
-		 * containing the specified page is skipped until its order
-		 * is new_order, since the folio will be worked on in next
-		 * iteration.
 		 */
 		for (new_folio = folio; new_folio != end_folio; new_folio = next) {
 			next = folio_next(new_folio);
-			/*
-			 * for buddy allocator like split, new_folio containing
-			 * @split_at page could be split again, thus do not
-			 * change stats yet. Wait until new_folio's order is
-			 * @new_order or stop_split is set to true by the above
-			 * xas_split() failure.
-			 */
-			if (new_folio == page_folio(split_at)) {
+			if (new_folio == page_folio(split_at))
 				folio = new_folio;
-				if (split_order != new_order && !stop_split)
-					continue;
-			}
 			if (is_anon)
 				mod_mthp_stat(folio_order(new_folio),
 					      MTHP_STAT_NR_ANON, 1);
 		}
 	}
 
-	return ret;
+	return 0;
 }
 
 bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
-- 
2.34.1