linux-kernel - Re: [PATCH v7 00/16] mm: folio_zero

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Message-ID: <87bjn8if4w.fsf@oracle.com>
Date: Wed, 17 Sep 2025 21:00:31 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        david@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
        peterz@...radead.org, namhyung@...nel.org, tglx@...utronix.de,
        willy@...radead.org, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages


Arnaldo Carvalho de Melo <acme@...nel.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