Re: [PATCH 0/4] mm: speed up ZONE_DEVICE memmap initialization

[Mike Rapoport]

Hi,

On Fri, May 15, 2026 at 04:20:41PM +0800, Li Zhe wrote:
> memmap_init_zone_device() can spend a substantial amount of time
> initializing large ZONE_DEVICE ranges because it repeats nearly
> identical struct page setup for every PFN.
> 
> This series reduces that overhead in four steps.
>
> Testing
> =======
> 
> Tests were run in a VM on an Intel Ice Lake server.
> 
> Two PMEM configurations were used:
>   - a 100 GB fsdax namespace configured with map=dev, which exercises
>     the nd_pmem rebind path (pfns_per_compound == 1)
>   - a 100 GB devdax namespace configured with align=2097152, which
>     exercises the dax_pmem rebind path (pfns_per_compound > 1)
> 
> For each configuration, the corresponding driver was unbound and
> rebound 30 times. Memmap initialization latency was collected from the
> pr_debug() output of memmap_init_zone_device().
> 
> The first bind is reported separately, and the average of subsequent
> rebinds is used as the steady-state result.
> 
> Performance
> ===========
> nd_pmem rebind, 100 GB fsdax namespace, map=dev
>   Base(v7.1-rc3):
>     First binding: 1486 ms
>     Average of subsequent rebinds: 273.52 ms
>   Full series:
>     First binding: 1272 ms
>     Average of subsequent rebinds: 104.59 ms
> 
> dax_pmem rebind, 100 GB devdax namespace, align=2097152
>   Base(v7.1-rc3):
>     First binding: 1515 ms
>     Average of subsequent rebinds: 313.45 ms
>   Full series:
>     First binding: 1286 ms
>     Average of subsequent rebinds: 116.93 ms

This is really good improvement!

It would be also interesting to see how the template approach would improve
"normal" memory map initialization.
 
> Li Zhe (4):
>   mm: factor zone-device page init helpers out of
>     __init_zone_device_page
>   mm: add a template-based fast path for zone-device page init
>   mm: extend the template fast path to zone-device compound tails
>   mm: use arch store helpers in zone-device template copies
> 
>  arch/x86/include/asm/struct_page_init.h |  28 +++
>  include/asm-generic/Kbuild              |   1 +
>  include/asm-generic/struct_page_init.h  |  17 ++
>  mm/mm_init.c                            | 260 +++++++++++++++++++++---
>  4 files changed, 280 insertions(+), 26 deletions(-)
>  create mode 100644 arch/x86/include/asm/struct_page_init.h
>  create mode 100644 include/asm-generic/struct_page_init.h
> 
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.