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Subject[PATCH 1/4] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
Date
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
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