linux-kernel - Re: [PATCH v2 5/8] selftests/mm: introduce helper to read every page in range

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Message-ID: <b785754d-ba6f-42db-9e44-66fd377aad03@arm.com>
Date: Mon, 12 Jan 2026 10:37:26 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: SeongJae Park <sj@...nel.org>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Mark Brown
 <broonie@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 5/8] selftests/mm: introduce helper to read every page
 in range

On 09/01/2026 02:30, SeongJae Park wrote:
> On Wed,  7 Jan 2026 16:48:39 +0000 Kevin Brodsky <kevin.brodsky@....com> wrote:
>
>> FORCE_READ(*addr) ensures that the compiler will emit a load from
>> addr. Several tests need to trigger such a load for every page in
>> the range [addr, addr + len), ensuring that every page is faulted
>> in, if it wasn't already.
>>
>> Introduce a new helper force_read_pages_in_range() that does exactly
>> that and replace existing loops with a call to it.
> Seems like a good cleanup to me.

Thanks for having a look at this series!

>> Some of those
>> loops have a different step size, but reading from every page is
>> appropriate in all cases.
> So the test program's behavior is slightly be changed.  I believe that
> shouldn't be problem, but I'm not that familiar with the test code, so not very
> sure.  I'd like to listen voices from people more familiar with those.
>
> Meanwhile, I'm curious what do you think about making the helper function
> receives the step size together, and let the callers just pass their current
> step size.

That's what I initially considered, but considering this discussion on
v1 [1] this doesn't seem to be justified. In hugetlb-madvise, reading
every page instead of every hugepage is unnecessary but still correct
and the overhead should be negligible. In split_huge_page_test, I don't
think there's any justification for reading every byte - the intention
is to fault in pages, like all the other cases this patch touches.

- Kevin

[1]
https://lore.kernel.org/all/a3ca6293-8f85-4489-a48e-eb8d0d3792c5@kernel.org/