From e3489f30ee7b813b09cc8c960f17a0ce0371ade9 Mon Sep 17 00:00:00 2001
From: Pengfei Li <pengfei.kernel@vivo.corp-partner.google.com>
Date: Mon, 7 Jul 2025 15:10:58 +0800
Subject: [PATCH] ANDROID: mm: Added early_param pcp_thp_order

Added early param "pcp_thp_order", which specifies the order of pcp used by THP.
This allows vendors to customize the order different from HPAGE_PMD_ORDER for
THP to use.

Bug: 431672372
Change-Id: Id2c8f3b03b74added54827ffbc33fd4e4bdf619e
Signed-off-by: Pengfei Li <pengfei.kernel@vivo.corp-partner.google.com>
---
 .../admin-guide/kernel-parameters.txt         |  5 ++++
 mm/page_alloc.c                               | 27 ++++++++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ab4c049faba9..97a787ca1ebf 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4759,6 +4759,11 @@
 
 	pcmv=		[HW,PCMCIA] BadgePAD 4
 
+	pcp_thp_order=	[MM]
+			Specify the order of the pcp used by THP.
+			The specified value must be no greater than HPAGE_PMD_ORDER
+			(default) and greater than 3 (PAGE_ALLOC_COSTLY_ORDER).
+
 	pd_ignore_unused
 			[PM]
 			Keep all power-domains already enabled by bootloader on,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d395554b7f70..da3ab3c781f9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -599,6 +599,27 @@ out:
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static unsigned int pcp_thp_order __read_mostly = HPAGE_PMD_ORDER;
+
+static int __init parse_pcp_thp_order(char *s)
+{
+	int err;
+	unsigned int order;
+
+	err = kstrtouint(s, 0, &order);
+	if (err)
+		return err;
+
+	if (order <= PAGE_ALLOC_COSTLY_ORDER || order > HPAGE_PMD_ORDER)
+		return -EINVAL;
+
+	pcp_thp_order = order;
+	return 0;
+}
+early_param("pcp_thp_order", parse_pcp_thp_order);
+#endif
+
 static inline unsigned int order_to_pindex(int migratetype, int order)
 {
 	bool __maybe_unused movable;
@@ -614,7 +635,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (order > PAGE_ALLOC_COSTLY_ORDER) {
-		VM_BUG_ON(order != HPAGE_PMD_ORDER);
+		VM_BUG_ON(order != pcp_thp_order);
 
 		movable = migratetype == MIGRATE_MOVABLE;
 #ifdef CONFIG_CMA
@@ -636,7 +657,7 @@ static inline int pindex_to_order(unsigned int pindex)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (pindex >= NR_LOWORDER_PCP_LISTS)
-		order = HPAGE_PMD_ORDER;
+		order = pcp_thp_order;
 #else
 	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
 #endif
@@ -649,7 +670,7 @@ static inline bool pcp_allowed_order(unsigned int order)
 	if (order <= PAGE_ALLOC_COSTLY_ORDER)
 		return true;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (order == HPAGE_PMD_ORDER)
+	if (order == pcp_thp_order)
 		return true;
 #endif
 	return false;