Re: [PATCH v3 2/5] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()

[Wei Yang <richard.weiyang@gmail.com>]

On Sun, Mar 25, 2018 at 08:02:16PM -0700, Jia He wrote:
>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. This patch only works when
>CONFIG_HAVE_ARCH_PFN_VALID is enable.
>
>Signed-off-by: Jia He <jia.he@hxt-semitech.com>
>---
> include/linux/memblock.h |  2 +-
> mm/memblock.c            | 73 +++++++++++++++++++++++++++++-------------------
> mm/page_alloc.c          |  3 +-
> 3 files changed, 47 insertions(+), 31 deletions(-)
>
>diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>index efbbe4b..a8fb2ab 100644
>--- a/include/linux/memblock.h
>+++ b/include/linux/memblock.h
>@@ -204,7 +204,7 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
> 
> #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>-unsigned long memblock_next_valid_pfn(unsigned long pfn);
>+unsigned long memblock_next_valid_pfn(unsigned long pfn, int *idx);
> #endif
> 
> /**
>diff --git a/mm/memblock.c b/mm/memblock.c
>index bea5a9c..06c1a08 100644
>--- a/mm/memblock.c
>+++ b/mm/memblock.c
>@@ -1102,35 +1102,6 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
> 		*out_nid = r->nid;
> }
> 
>-#ifdef CONFIG_HAVE_ARCH_PFN_VALID
>-unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>-{
>-	struct memblock_type *type = &memblock.memory;
>-	unsigned int right = type->cnt;
>-	unsigned int mid, left = 0;
>-	phys_addr_t addr = PFN_PHYS(++pfn);
>-
>-	do {
>-		mid = (right + left) / 2;
>-
>-		if (addr < type->regions[mid].base)
>-			right = mid;
>-		else if (addr >= (type->regions[mid].base +
>-				  type->regions[mid].size))
>-			left = mid + 1;
>-		else {
>-			/* addr is within the region, so pfn is valid */
>-			return pfn;
>-		}
>-	} while (left < right);
>-
>-	if (right == type->cnt)
>-		return -1UL;
>-	else
>-		return PHYS_PFN(type->regions[right].base);
>-}
>-#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
>-
> /**
>  * memblock_set_node - set node ID on memblock regions
>  * @base: base of area to set node ID for
>@@ -1162,6 +1133,50 @@ int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,
> }
> #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
> 
>+#ifdef CONFIG_HAVE_ARCH_PFN_VALID
>+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 */
                             ^^^  pfn

>+	if (*last_idx != -1) {
>+		start_pfn = PFN_DOWN(type->regions[*last_idx].base);

To me, it should be PFN_UP().

>+		end_pfn = PFN_DOWN(type->regions[*last_idx].base +
>+				type->regions[*last_idx].size);
>+
>+		if (pfn < end_pfn && pfn > start_pfn)

Could be (pfn < end_pfn && pfn >= start_pfn)?

pfn == start_pfn is also a valid address.

>+			return pfn;
>+	}
>+
>+	/* slow path, do the binary searching */
>+	do {
>+		mid = (right + left) / 2;
>+
>+		if (addr < type->regions[mid].base)
>+			right = mid;
>+		else if (addr >= (type->regions[mid].base +
>+				  type->regions[mid].size))
>+			left = mid + 1;
>+		else {
>+			*last_idx = mid;
>+			return pfn;
>+		}
>+	} while (left < right);
>+
>+	if (right == type->cnt)
>+		return -1UL;
>+
>+	*last_idx = right;
>+
>+	return PHYS_PFN(type->regions[*last_idx].base);
>+}
>+#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/

The same comment as Daniel, you are moving the function out of
CONFIG_HAVE_MEMBLOCK_NODE_MAP.

>+
> static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
> 					phys_addr_t align, phys_addr_t start,
> 					phys_addr_t end, int nid, ulong flags)
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index 2a967f7..0bb0274 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -5459,6 +5459,7 @@ 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
>@@ -5490,7 +5491,7 @@ 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

-- 
Wei Yang
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