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From:   Jia He <hejianet@gmail.com>
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Subject: [PATCH 1/4] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
Date:   Wed, 21 Mar 2018 01:09:53 -0700
Message-Id: <1521619796-3846-2-git-send-email-hejianet@gmail.com>
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Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
where possible") optimized the loop in memmap_init_zone(). But there is
still some room for improvement. E.g. if pfn and pfn+1 are in the same
memblock region, we can simply pfn++ instead of doing the binary search
in memblock_next_valid_pfn.

Signed-off-by: Jia He <jia.he@hxt-semitech.com>
---
 include/linux/memblock.h |  3 +--
 mm/memblock.c            | 23 +++++++++++++++++++----
 mm/page_alloc.c          |  3 ++-
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index b7aa3ff..9471db4 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -203,8 +203,7 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
 	     i >= 0; __next_mem_pfn_range(&i, nid, p_start, p_end, p_nid))
 #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
 
-unsigned long memblock_next_valid_pfn(unsigned long pfn);
-
+unsigned long memblock_next_valid_pfn(unsigned long pfn, int *last_idx);
 /**
  * for_each_free_mem_range - iterate through free memblock areas
  * @i: u64 used as loop variable
diff --git a/mm/memblock.c b/mm/memblock.c
index c87924d..a9e8da4 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1133,13 +1133,26 @@ int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,
 }
 #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
 
-unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
+unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
+							int *last_idx)
 {
 	struct memblock_type *type = &memblock.memory;
 	unsigned int right = type->cnt;
 	unsigned int mid, left = 0;
+	unsigned long start_pfn, end_pfn;
 	phys_addr_t addr = PFN_PHYS(++pfn);
 
+	/* fast path, return pfh+1 if next pfn is in the same region */
+	if (*last_idx != -1) {
+		start_pfn = PFN_DOWN(type->regions[*last_idx].base);
+		end_pfn = PFN_DOWN(type->regions[*last_idx].base +
+				type->regions[*last_idx].size);
+
+		if (pfn < end_pfn && pfn > start_pfn)
+			return pfn;
+	}
+
+	/* slow path, do the binary searching */
 	do {
 		mid = (right + left) / 2;
 
@@ -1149,15 +1162,17 @@ unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
 				  type->regions[mid].size))
 			left = mid + 1;
 		else {
-			/* addr is within the region, so pfn is valid */
+			*last_idx = mid;
 			return pfn;
 		}
 	} while (left < right);
 
 	if (right == type->cnt)
 		return -1UL;
-	else
-		return PHYS_PFN(type->regions[right].base);
+
+	*last_idx = right;
+
+	return PHYS_PFN(type->regions[*last_idx].base);
 }
 
 static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3899209..f28c62c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5456,6 +5456,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 	unsigned long end_pfn = start_pfn + size;
 	pg_data_t *pgdat = NODE_DATA(nid);
 	unsigned long pfn;
+	int idx = -1;
 	unsigned long nr_initialised = 0;
 	struct page *page;
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
@@ -5487,7 +5488,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 			 * 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) - 1;
+			pfn = memblock_next_valid_pfn(pfn, &idx) - 1;
 #endif
 			continue;
 		}
-- 
2.7.4