Re: [PATCH v2 0/2] mm: optimize HugeTLB bootmem hugepage init

[Mike Rapoport <rppt@kernel.org>]

Hi,

On Tue, Nov 10, 2026 at 07:48:57PM +0800, Li Zhe wrote:
> This series speeds up the fallback initialization path for HugeTLB tail
> struct pages during boot-time hugepage allocation, when HugeTLB vmemmap
> optimization (HVO) is unavailable or fails.
> 
> Patch 1 factors the existing ZONE_DEVICE template-copy operation into
> memmap_init_page_from_template().
> 
> Patch 2 reuses that helper in hugetlb_folio_init_tail_vmemmap():
> initialize the first tail page normally, copy it into a local template,
> then initialize the remaining tail pages by refreshing only PFN-dependent
> fields before copying the template.
> 
> In the earlier discussion, Mike asked whether the same kind of
> template-based initialization also helps the ordinary struct page
> initialization path:
> 
> https://lore.kernel.org/all/akfB6Qe-jKDEMUxz@kernel.org/
> 
> I tested that direction as well, but did not see a measurable benefit
> for ordinary struct page initialization. The measurable improvement I
> could find is in the HugeTLB bootmem hugepage tail path, where gigantic
> pages can require initializing a large number of tail struct pages when
> HVO does not cover the allocation.
> 
> Tested on an arm64 QEMU/KVM guest with 4K base pages and 64 boot-time 1G
> hugepages. HVO is unavailable on arm64 in v7.4-rc1, so the fallback tail
> initialization path is exercised.
> 
> Results averaged over five boots, measured with a temporary
> jiffies-based printk:
> 
>   base (v7.4-rc1):  318.4 ms
>   with this patch:  202.4 ms

Are there numbers for x86 without HVO as well?
We need to be sure this does not regress that use case.
 
> This is a 36.43% reduction in the measured fallback tail initialization
> time. The temporary measurement instrumentation is not part of this
> series.
> 
> Li Zhe (2):
>   mm/mm_init: factor out memmap_init_page_from_template()
>   mm/hugetlb: optimize bootmem hugepage tail vmemmap init
> 
>  mm/hugetlb.c | 20 +++++++++++++++-----
>  mm/mm_init.c | 34 ++++++++++++++++++++--------------
>  mm/mm_init.h |  2 ++
>  3 files changed, 37 insertions(+), 19 deletions(-)
> 
> ---
> v1: https://lore.kernel.org/all/20261105120615.16817-1-lizhe.67@bytedance.com/#t
> 
> Changes in v2:
> - Add a comment for the template-before-copy ordering, as suggested by
>   Muchun Song.
> - Drop the empty-range guard in hugetlb_folio_init_tail_vmemmap()
>   as suggested by Balbir Singh and Mike Rapoport; current callers are
>   expected to pass a non-empty range.
> 
> -- 
> 2.20.1

-- 
Sincerely yours,
Mike.