Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Ankur Arora <ankur.a.arora@oracle.com>]

Arnaldo Carvalho de Melo <acme@kernel.org> writes:

> On Wed, Sep 17, 2025 at 08:24:02AM -0700, Ankur Arora wrote:
>> This series adds clearing of contiguous page ranges for hugepages,
>> improving on the current page-at-a-time approach in two ways:
>>
>>  - amortizes the per-page setup cost over a larger extent
>>
>>  - when using string instructions, exposes the real region size
>>    to the processor.
>>
>> A processor could use a knowledge of the extent to optimize the
>> clearing. AMD Zen uarchs, as an example, elide allocation of
>> cachelines for regions larger than L3-size.
>>
>> Demand faulting a 64GB region shows performance improvements:
>>
>>  $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5
>>
>>                  mm/folio_zero_user    x86/folio_zero_user       change
>>                   (GB/s  +- %stdev)     (GB/s  +- %stdev)
>>
>>    pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*
>>
>>    pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
>>    pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy
>>
>> [#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
>> allocation, which is higher than the maximum extent used on x86
>> (ARCH_CONTIG_PAGE_NR=8MB), so preempt=none|voluntary sees no improvement
>> with pg-sz=1GB.
>
> I'm picking up the tools/perf part for perf-tools-next (v6.18), already
> almost 100% reviewed by Namhyung.

Thanks!

--
ankur