Subject: [PATCH v7 3/7] mm/memory_hotplug: Allow architecture to override memmap on memory support check

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 1 Aug 2023 10:11:12 +0530

Some architectures would want different restrictions. Hence add an
architecture-specific override.

The PMD_SIZE check is moved there.

Acked-by: David Hildenbrand <[email-masked]>
Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 mm/memory_hotplug.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index eca32ccd45cc..746cb7c08c64 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1247,10 +1247,26 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 	return device_online(&mem->dev);
 }
 
+static inline unsigned long memory_block_memmap_size(void)
+{
+	return PHYS_PFN(memory_block_size_bytes()) * sizeof(struct page);
+}
+
+#ifndef arch_supports_memmap_on_memory
+static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size)
+{
+	/*
+	 * As default, we want the vmemmap to span a complete PMD such that we
+	 * can map the vmemmap using a single PMD if supported by the
+	 * architecture.
+	 */
+	return IS_ALIGNED(vmemmap_size, PMD_SIZE);
+}
+#endif
+
 static bool mhp_supports_memmap_on_memory(unsigned long size)
 {
-	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
-	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
+	unsigned long vmemmap_size = memory_block_memmap_size();
 	unsigned long remaining_size = size - vmemmap_size;
 
 	/*
@@ -1281,8 +1297,8 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
 	 */
 	return mhp_memmap_on_memory() &&
 	       size == memory_block_size_bytes() &&
-	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
-	       IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
+	       IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT)) &&
+	       arch_supports_memmap_on_memory(vmemmap_size);
 }
 
 /*
-- 
2.41.0