Re: [PATCH v9 0/6] optimize memblock_next_valid_pfn and early_pfn_valid on arm and arm64

[Jia He]

Hi Michal
Thanks for the comments

On 7/2/2018 7:40 PM, Michal Hocko Wrote:
> On Fri 29-06-18 10:29:17, Jia He wrote:
>> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
>> where possible") tried to optimize the loop in memmap_init_zone(). But
>> there is still some room for improvement.
> 
> It would be great to shortly describe those optimization from high level
> POV.

Ok

> 
>>
>> Patch 1 introduce new config to make codes more generic
>> Patch 2 remain the memblock_next_valid_pfn on arm and arm64
>> Patch 3 optimizes the memblock_next_valid_pfn()
>> Patch 4~6 optimizes the early_pfn_valid()
>>
>> As for the performance improvement, after this set, I can see the time
>> overhead of memmap_init() is reduced from 27956us to 13537us in my
>> armv8a server(QDF2400 with 96G memory, pagesize 64k).
> 
> So this is 13ms saving when booting 96G machine. Is this really worth
> the additional code? Are there any other benefits?

hmm.. Currently my answer is no.
But I believe it can shorten the boot time when the memory is larger than n TBs.
-- 
Cheers,
Jia

> [...]
>>  arch/arm/Kconfig          |  4 +++
>>  arch/arm/mm/init.c        |  1 +
>>  arch/arm64/Kconfig        |  4 +++
>>  arch/arm64/mm/init.c      |  1 +
>>  include/linux/early_pfn.h | 79 +++++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/memblock.h  |  2 ++
>>  include/linux/mmzone.h    | 18 ++++++++++-
>>  mm/Kconfig                |  3 ++
>>  mm/memblock.c             |  9 ++++++
>>  mm/page_alloc.c           |  5 ++-
>>  10 files changed, 124 insertions(+), 2 deletions(-)
>>  create mode 100644 include/linux/early_pfn.h
>