linux-kernel - Re: [PATCH v5 13/14] mm: memory: support clearing page-extents

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Message-ID: <87bjpqocdg.fsf@oracle.com>
Date: Fri, 11 Jul 2025 10:39:39 -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 13/14] mm: memory: support clearing page-extents


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

> On 10.07.25 02:59, Ankur Arora wrote:
>> folio_zero_user() is constrained to clear in a page-at-a-time
>> fashion because it supports CONFIG_HIGHMEM which means that kernel
>> mappings for pages in a folio are not guaranteed to be contiguous.
>> We don't have this problem when running under configurations with
>> CONFIG_CLEAR_PAGE_EXTENT (implies !CONFIG_HIGHMEM), so zero in
>> longer page-extents.
>> This is expected to be faster because the processor can now optimize
>> the clearing based on the knowledge of the extent.
>>
>
> I'm curious: how did we end up "page extent" terminology? :)

After trying all the others! I tried multi-page and contig_clear_pages
and finally decided to go with page-extent since clear_pages()
essentially takes a page-extent as an argument.

> "CONFIG_CLEAR_CONTIG_PAGES" or sth. like that would be a bit clearer (pun
> intended), at least to me.

Oddly enough I tried CONFIG_CONTIG_CLEAR_PAGES and
CONFIG_CLEAR_PAGES_CONTIG but those read a little awkwardly.

CONFIG_CLEAR_CONTIG_PAGES reads better. Should have tried moving the
CONTIG to the middle as well :D.

> We use "CONTIG" pages already in different MM context.
>
> "page extent" reminds of "page_ext", which is "page extension" ...

Yeah I see that in the Kconfig now. Will switch to this one.

Thanks

--
ankur