From: Wei Yang <richard.weiyang@gmail.com>
Date: Tue, 21 Oct 2025 21:21:42 +0000 (+0000)
Subject: mm/huge_memory: optimize old_order derivation during folio splitting
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f0b1602871f8506c5aa704e9641b004f21918759;p=thirdparty%2Fkernel%2Flinux.git

mm/huge_memory: optimize old_order derivation during folio splitting

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.

Link: https://lkml.kernel.org/r/20251021212142.25766-5-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: wang lian <lianux.mm@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 52c4114a17f29..0a521cf9b10a4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3402,8 +3402,8 @@ 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;
 
 	/*
@@ -3413,14 +3413,11 @@ 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) {
 			/*
@@ -3447,7 +3444,13 @@ 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;