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

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Message-ID: <20260113005530.101000-1-sj@kernel.org>
Date: Mon, 12 Jan 2026 16:55:29 -0800
From: SeongJae Park <sj@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: SeongJae Park <sj@...nel.org>,
	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 Mon, 12 Jan 2026 10:37:26 +0100 Kevin Brodsky <kevin.brodsky@....com> wrote:

> 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!

My pleasure!

> 
> >> 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/

Makes sense, thank you for the link!

Please feel free to add

Reviewed-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

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