linux-kernel - Re: [PATCH v5 12/14] mm: add config option for clearing page-extents

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Message-ID: <878qkuprku.fsf@oracle.com>
Date: Fri, 11 Jul 2025 10:25:53 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
        peterz@...radead.org, acme@...nel.org, namhyung@...nel.org,
        tglx@...utronix.de, willy@...radead.org, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v5 12/14] mm: add config option for clearing page-extents


David Hildenbrand <david@...hat.com> writes:

> On 10.07.25 02:59, Ankur Arora wrote:
>> Add CONFIG_CLEAR_PAGE_EXTENT to allow clearing of page-extents
>> where architecturally supported.
>> This is only available with !CONFIG_HIGHMEM because the intent is to
>> use architecture support to clear contiguous extents in a single
>> operation (ex. via FEAT_MOPS on arm64, string instructions on x86)
>> which excludes any possibility of interspersing kmap()/kunmap().
>> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
>> ---
>>   mm/Kconfig | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 781be3240e21..a74a5e02de28 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -910,6 +910,15 @@ config NO_PAGE_MAPCOUNT
>>     endif # TRANSPARENT_HUGEPAGE
>>   +config CLEAR_PAGE_EXTENT
>> +	def_bool y
>> +	depends on !HIGHMEM && ARCH_HAS_CLEAR_PAGES
>> +	depends on TRANSPARENT_HUGEPAGE || HUGETLBFS
>> +
>> +	help
>> +	  Use architectural support for clear_pages() to zero page-extents.
>> +	  This is likely to be faster than zeroing page-at-a-time.
>> +
>
> IIRC, adding a help text will make this option be configurable by the user, no?

I tried changing the value in the generated .config by hand and that
reverted back to the computed value. So, I think this isn't configurable
by the user.

>From a quick look at the kbuild documentation, for this to be user
selectable it needs a prompt of some kind.

That said, the help text doesn't add anything here. Will remove.

> This seems like something we can just keep internal, right?

Agreed.

Thanks for the review!

--
ankur