[Patch v3 4/4] mm/huge_memory: optimize old_order derivation during folio splitting

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

Folio splitting requires both the folio's original order (@old_order)
and the new target order (@split_order).

In the current implementation, @old_order is repeatedly retrieved using
folio_order().

However, for every iteration after the first, the folio being split is
the result of the previous split, meaning its order is already known to
be equal to the previous iteration's @split_order.

This commit optimizes the logic:

  * Instead of calling folio_order(), we now set @old_order directly to
    the value of @split_order from the previous iteration.

This change avoids unnecessary function calls and simplifies the loop
setup.

Also it removes a check for non-existent case, since for uniform
splitting we only do split when @split_order == @new_order.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: wang lian <lianux.mm@gmail.com>
---
 mm/huge_memory.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 093b3ffb180f..a4fa8b0e5b5a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3596,8 +3596,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 		struct address_space *mapping, bool uniform_split)
 {
 	const bool is_anon = folio_test_anon(folio);
-	int order = folio_order(folio);
-	int start_order = uniform_split ? new_order : order - 1;
+	int old_order = folio_order(folio);
+	int start_order = uniform_split ? new_order : old_order - 1;
 	int split_order;
 
 	folio_clear_has_hwpoisoned(folio);
@@ -3609,14 +3609,11 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 	for (split_order = start_order;
 	     split_order >= new_order;
 	     split_order--) {
-		int old_order = folio_order(folio);
 		int nr_new_folios = 1UL << (old_order - split_order);
 
 		/* order-1 anonymous folio is not supported */
 		if (is_anon && split_order == 1)
 			continue;
-		if (uniform_split && split_order != new_order)
-			continue;
 
 		if (mapping) {
 			/*
@@ -3643,7 +3640,13 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 			mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1);
 			mod_mthp_stat(split_order, MTHP_STAT_NR_ANON, nr_new_folios);
 		}
+		/*
+		 * 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.
+		 */
 		folio = page_folio(split_at);
+		old_order = split_order;
 	}
 
 	return 0;
-- 
2.34.1