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Subject[PATCH v5 2/5] arm: arm64: 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>
---
arch/arm/include/asm/page.h | 1 +
arch/arm/mm/init.c | 28 ++++++++++++++++++++++------
arch/arm64/include/asm/page.h | 1 +
arch/arm64/mm/init.c | 28 ++++++++++++++++++++++------
4 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
index 489875c..f38909c 100644
--- a/arch/arm/include/asm/page.h
+++ b/arch/arm/include/asm/page.h
@@ -157,6 +157,7 @@ extern void copy_page(void *to, const void *from);
typedef struct page *pgtable_t;

#ifdef CONFIG_HAVE_ARCH_PFN_VALID
+extern int early_region_idx;
extern int pfn_valid(unsigned long);
extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
#define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 0fb85ca..06ed190 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -193,6 +193,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
}

#ifdef CONFIG_HAVE_ARCH_PFN_VALID
+int early_region_idx __meminitdata = -1;
+
int pfn_valid(unsigned long pfn)
{
return memblock_is_map_memory(__pfn_to_phys(pfn));
@@ -203,28 +205,42 @@ EXPORT_SYMBOL(pfn_valid);
unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
{
struct memblock_type *type = &memblock.memory;
+ struct memblock_region *regions = type->regions;
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 pfn+1 if next pfn is in the same region */
+ if (early_region_idx != -1) {
+ start_pfn = PFN_DOWN(regions[early_region_idx].base);
+ end_pfn = PFN_DOWN(regions[early_region_idx].base +
+ regions[early_region_idx].size);
+
+ if (pfn >= start_pfn && pfn < end_pfn)
+ return pfn;
+ }
+
+ /* slow path, do the binary searching */
do {
mid = (right + left) / 2;

- if (addr < type->regions[mid].base)
+ if (addr < regions[mid].base)
right = mid;
- else if (addr >= (type->regions[mid].base +
- type->regions[mid].size))
+ else if (addr >= (regions[mid].base + regions[mid].size))
left = mid + 1;
else {
- /* addr is within the region, so pfn is valid */
+ early_region_idx = mid;
return pfn;
}
} while (left < right);

if (right == type->cnt)
return -1UL;
- else
- return PHYS_PFN(type->regions[right].base);
+
+ early_region_idx = right;
+
+ return PHYS_PFN(regions[early_region_idx].base);
}
EXPORT_SYMBOL(memblock_next_valid_pfn);
#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index e57d3f2..f0d8c8e5 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -38,6 +38,7 @@ extern void clear_page(void *to);
typedef struct page *pgtable_t;

#ifdef CONFIG_HAVE_ARCH_PFN_VALID
+extern int early_region_idx;
extern int pfn_valid(unsigned long);
extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
#define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 13e43ff..342e4e2 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -285,6 +285,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
#endif /* CONFIG_NUMA */

#ifdef CONFIG_HAVE_ARCH_PFN_VALID
+int early_region_idx __meminitdata = -1;
+
int pfn_valid(unsigned long pfn)
{
return memblock_is_map_memory(pfn << PAGE_SHIFT);
@@ -295,28 +297,42 @@ EXPORT_SYMBOL(pfn_valid);
unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
{
struct memblock_type *type = &memblock.memory;
+ struct memblock_region *regions = type->regions;
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 pfn+1 if next pfn is in the same region */
+ if (early_region_idx != -1) {
+ start_pfn = PFN_DOWN(regions[early_region_idx].base);
+ end_pfn = PFN_DOWN(regions[early_region_idx].base +
+ regions[early_region_idx].size);
+
+ if (pfn >= start_pfn && pfn < end_pfn)
+ return pfn;
+ }
+
+ /* slow path, do the binary searching */
do {
mid = (right + left) / 2;

- if (addr < type->regions[mid].base)
+ if (addr < regions[mid].base)
right = mid;
- else if (addr >= (type->regions[mid].base +
- type->regions[mid].size))
+ else if (addr >= (regions[mid].base + regions[mid].size))
left = mid + 1;
else {
- /* addr is within the region, so pfn is valid */
+ early_region_idx = mid;
return pfn;
}
} while (left < right);

if (right == type->cnt)
return -1UL;
- else
- return PHYS_PFN(type->regions[right].base);
+
+ early_region_idx = right;
+
+ return PHYS_PFN(regions[early_region_idx].base);
}
EXPORT_SYMBOL(memblock_next_valid_pfn);
#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
--
2.7.4
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