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

[Jia He <hejianet@gmail.com>]

On 3/28/2018 1:17 AM, Daniel Vacek Wrote:
> On Mon, Mar 26, 2018 at 5:02 AM, Jia He <hejianet@gmail.com> 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 */
>> +       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;
>> +
>> +               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*/
>> +
>>   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
>>
> So the function is only defined with CONFIG_HAVE_ARCH_PFN_VALID but
> it's called with CONFIG_HAVE_MEMBLOCK_NODE_MAP? The definition should
> likely depend on both options as the function really depends on both
> conditions. Otherwise it should be defined nop.
>
> --nX
>
Yes, thanks

-- 
Cheers,
Jia