Re: [PATCH v4 00/13] x86/mm: Add multi-page clearing

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

Raghavendra K T <raghavendra.kt@amd.com> writes:

> On 6/16/2025 10:52 AM, Ankur Arora wrote:
>> This series adds multi-page clearing 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 that as a hint to optimize based
>>     on the full extent size. AMD Zen uarchs, as an example, elide
>>     allocation of cachelines for regions larger than L3-size.
>> Demand faulting a 64GB region shows good performance improvements:
>>   $ perf bench mem map -p $page-size -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%
>>    pg-sz=1GB       17.51  +- 1.19%        40.03  +-  7.26% [#]   +129.9%
>> [#] Only with preempt=full|lazy because cooperatively preempted models
>> need regular invocations of cond_resched(). This limits the extent
>> sizes that can be cleared as a unit.
>> Raghavendra also tested on AMD Genoa and that shows similar
>> improvements [1].
>>
> [...]
> Sorry for coming back late on this:
> It was nice to have it integrated to perf bench mem (easy to test :)).
>
> I do see similar (almost same) improvement again with the rebased kernel
> and patchset.
> Tested only preempt=lazy and boost=1
>
> base       6.16-rc4 + 1-9 patches of this series
> patched =  6.16-rc4 + all patches
>
> SUT: Genoa+ AMD EPYC 9B24
>
>  $ perf bench mem map -p $page-size -f populate -s 64GB -l 10
>                    base               patched              change
>   pg-sz=2MB       12.731939 GB/sec    26.304263 GB/sec     106.6%
>   pg-sz=1GB       26.232423 GB/sec    61.174836 GB/sec     133.2%

Thanks for trying them out. Looks great.

--
ankur