[PATCH] [RFC] mm: page_alloc: skip over regions of invalid pfns on UMA

[Eugeniu Rosca]

As a result of bisecting the v4.10..v4.11 commit range, it was
determined that commits [1] and [2] are both responsible of a ~170ms
early startup improvement on Rcar-H3-ES20 arm64 platform.

Since Rcar Gen3 family is not NUMA, we don't define CONFIG_NUMA in the
rcar3 defconfig, but this is how the boot time improvement is lost.

Make optimization [2] available on arm64 UMA systems and reduce the
time spent in memmap_init_zone() from 201ms to 34ms. Testing this
change on Apollo Lake SoC, boot time didn't change.

[1] commit 0f84832fb8f9 ("arm64: defconfig: Enable NUMA and NUMA_BALANCING")
[2] commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns where possible")
[3] 201ms spent in memmap_init_zone() on H3ULCB before this patch (NUMA not set)
[    2.048087] On node 0 totalpages: 1003520
[    2.048091]   DMA zone: 3392 pages used for memmap
[    2.048094]   DMA zone: 0 pages reserved
[    2.048096]   DMA zone: 217088 pages, LIFO batch:31
[    2.048099] memmap_init_zone: start
[    2.068881] memmap_init_zone: end
[    2.068884]   Normal zone: 12288 pages used for memmap
[    2.068888]   Normal zone: 786432 pages, LIFO batch:31
[    2.068890] memmap_init_zone: start
[    2.249791] memmap_init_zone: end
[    2.249824] psci: probing for conduit method from DT.

[4] 34ms spent in memmap_init_zone() on H3ULCB after this patch
[    2.072935] On node 0 totalpages: 1003520
[    2.072940]   DMA zone: 3392 pages used for memmap
[    2.072942]   DMA zone: 0 pages reserved
[    2.072945]   DMA zone: 217088 pages, LIFO batch:31
[    2.072948] memmap_init_zone: start
[    2.080442] memmap_init_zone: end
[    2.080446]   Normal zone: 12288 pages used for memmap
[    2.080449]   Normal zone: 786432 pages, LIFO batch:31
[    2.080451] memmap_init_zone: start
[    2.107935] memmap_init_zone: end
[    2.107965] psci: probing for conduit method from DT.

Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
---
 include/linux/memblock.h | 3 ++-
 mm/memblock.c            | 2 ++
 mm/page_alloc.c          | 2 --
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 7ed0f7782d16..876c0a334164 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -182,12 +182,13 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
 	return m->flags & MEMBLOCK_NOMAP;
 }
 
+unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn);
+
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
 int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
 			    unsigned long  *end_pfn);
 void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
 			  unsigned long *out_end_pfn, int *out_nid);
-unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn);
 
 /**
  * for_each_mem_pfn_range - early memory pfn range iterator
diff --git a/mm/memblock.c b/mm/memblock.c
index 46aacdfa4f4d..ad48cf200e3b 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1100,6 +1100,7 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
 	if (out_nid)
 		*out_nid = r->nid;
 }
+#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
 
 unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
 						      unsigned long max_pfn)
@@ -1129,6 +1130,7 @@ unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
 		return min(PHYS_PFN(type->regions[right].base), max_pfn);
 }
 
+#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
 /**
  * memblock_set_node - set node ID on memblock regions
  * @base: base of area to set node ID for
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7e5e775e97f4..defd5ef08c54 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5344,14 +5344,12 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 			goto not_early;
 
 		if (!early_pfn_valid(pfn)) {
-#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
 			/*
 			 * Skip to the pfn preceding the next valid one (or
 			 * end_pfn), such that we hit a valid pfn (or end_pfn)
 			 * on our next iteration of the loop.
 			 */
 			pfn = memblock_next_valid_pfn(pfn, end_pfn) - 1;
-#endif
 			continue;
 		}
 		if (!early_pfn_in_nid(pfn, nid))
-- 
2.14.2