Subject: [PATCH] aarch64/mm: speedup memory initialisation

From: Hubert Ralf <[email-masked]>
Date: Tue, 10 Sep 2019 08:59:07 +0000

On ARM64 memmap_init_zone is used during bootmem_init, which iterates over
all pages in the memory starting at the lowest address until the highest
address is reached. On arm64 this ends up in searching a memmory region
containing for each single page between lowest and highest available
physicall address.

Having a sparse memory system there may be some big holes in the
memory map. For each page in this holes a lookup is done, which is
implemented as a binary search on the available memory blocks.

Adding a memmap_init for aarch64 to do the init only for the available
memory areas reduces the time needed for initialising memory on startup.
On a Renesas R-CAR M3 based system with a total hole of 20GB bootmem_init
execution time is reduced from 378ms to 84ms.

Signed-off-by: Ralf Hubert <[email-masked]>
---
 arch/arm64/include/asm/pgtable.h |  7 +++++++
 arch/arm64/mm/init.c             | 24 ++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index e09760ece844..8c6eefc08b0b 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -298,6 +298,13 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
 	return (lhs == rhs);
 }
 
+#ifdef CONFIG_SPARSEMEM
+/* arch mem_map init routine is needed due to holes in a memmap */
+#   define __HAVE_ARCH_MEMMAP_INIT
+	void memmap_init(unsigned long size, int nid, unsigned long zone,
+			 unsigned long start_pfn);
+#endif /* CONFIG_SPARSEMEM */
+
 /*
  * Huge pte definitions.
  */
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index f3c795278def..206b28310872 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -250,6 +250,30 @@ int pfn_valid(unsigned long pfn)
 }
 EXPORT_SYMBOL(pfn_valid);
 
+#ifdef CONFIG_SPARSEMEM
+void __meminit
+memmap_init(unsigned long size, int nid, unsigned long zone,
+	    unsigned long start_pfn)
+{
+	struct memblock_region *reg;
+
+	for_each_memblock(memory, reg) {
+		unsigned long start = memblock_region_memory_base_pfn(reg);
+		unsigned long end = memblock_region_memory_end_pfn(reg);
+
+		if (start < start_pfn)
+			start = start_pfn;
+		if (end > start_pfn + size)
+			end = start_pfn + size;
+
+		if (start < end) {
+			memmap_init_zone(end - start, nid, zone, start,
+					 MEMMAP_EARLY, NULL);
+		}
+	}
+}
+#endif /* CONFIG_SPARSEMEM */
+
 static phys_addr_t memory_limit = PHYS_ADDR_MAX;
 
 /*
-- 
2.23.0

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