linux-kernel - [PATCH] mm/mm_init.c: remove spinlock in early_pfn_to

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Date:   Wed, 14 Jun 2023 19:03:24 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     gregkh@...uxfoundation.org, rafael@...nel.org, rppt@...nel.org,
        akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH] mm/mm_init.c: remove spinlock in early_pfn_to_nid()

When the system boots, only one cpu is enabled before smp_init().
So the spinlock is not needed in most cases, remove it.

Add spinlock in get_nid_for_pfn() because it is after smp_init().

Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 drivers/base/node.c | 11 +++++++++--
 mm/mm_init.c        | 18 +++---------------
 2 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 9de524e56307..844102570ff2 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -748,8 +748,15 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
 static int __ref get_nid_for_pfn(unsigned long pfn)
 {
 #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
-	if (system_state < SYSTEM_RUNNING)
-		return early_pfn_to_nid(pfn);
+	static DEFINE_SPINLOCK(early_pfn_lock);
+	int nid;
+
+	if (system_state < SYSTEM_RUNNING) {
+		spin_lock(&early_pfn_lock);
+		nid = early_pfn_to_nid(pfn);
+		spin_unlock(&early_pfn_lock);
+		return nid;
+	}
 #endif
 	return pfn_to_nid(pfn);
 }
diff --git a/mm/mm_init.c b/mm/mm_init.c
index d393631599a7..5895a30435ee 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -584,11 +584,11 @@ struct mminit_pfnnid_cache {
 static struct mminit_pfnnid_cache early_pfnnid_cache __meminitdata;
 
 /*
- * Required by SPARSEMEM. Given a PFN, return what node the PFN is on.
+ * Given a PFN, return what node the PFN is on.
  */
-static int __meminit __early_pfn_to_nid(unsigned long pfn,
-					struct mminit_pfnnid_cache *state)
+int __meminit early_pfn_to_nid(unsigned long pfn)
 {
+	struct mminit_pfnnid_cache *state = &early_pfnnid_cache;
 	unsigned long start_pfn, end_pfn;
 	int nid;
 
@@ -601,20 +601,8 @@ static int __meminit __early_pfn_to_nid(unsigned long pfn,
 		state->last_end = end_pfn;
 		state->last_nid = nid;
 	}
-
-	return nid;
-}
-
-int __meminit early_pfn_to_nid(unsigned long pfn)
-{
-	static DEFINE_SPINLOCK(early_pfn_lock);
-	int nid;
-
-	spin_lock(&early_pfn_lock);
-	nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
 	if (nid < 0)
 		nid = first_online_node;
-	spin_unlock(&early_pfn_lock);
 
 	return nid;
 }
-- 
2.25.1