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SubjectRe: [PATCH v3 2/5] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
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
Help you, Help me

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