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

[Michal Hocko <mhocko@kernel.org>]

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.

> 
> 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?
[...]
>  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

-- 
Michal Hocko
SUSE Labs