mm/memory_hotplug: allow architecture to override memmap on memory su…

…pport check

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

The PMD_SIZE check is moved there.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Aneesh Kumar K.V <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Vishal Verma <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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);
 }
 
 /*