linux-kernel - Re: [PATCH] selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"

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Message-Id: <20250716151543.998b121a58064011e9ce68cb@linux-foundation.org>
Date: Wed, 16 Jul 2025 15:15:43 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: wang lian <lianux.mm@...il.com>
Cc: broonie@...nel.org, david@...hat.com, lorenzo.stoakes@...cle.com,
 sj@...nel.org, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, brauner@...nel.org, jannh@...gle.com,
 Liam.Howlett@...cle.com, shuah@...nel.org, vbabka@...e.cz,
 ludovico.zy.wu@...il.com, gkwang@...x-info.com, p1ucky0923@...il.com,
 ryncsn@...il.com, zijing.zhang@...ton.me
Subject: Re: [PATCH] selftests/mm: reuse FORCE_READ to replace
 "asm volatile("" : "+r" (XXX));"

On Wed, 16 Jul 2025 20:31:26 +0800 wang lian <lianux.mm@...il.com> wrote:

> Several mm selftests use the `asm volatile("" : "+r" (variable));`
> construct to force a read of a variable, preventing the compiler from
> optimizing away the memory access. This idiom is cryptic and duplicated
> across multiple test files.
> 
> Following a suggestion from David[1], this patch refactors this
> common pattern into a FORCE_READ() macro
> 
>  tools/testing/selftests/mm/cow.c              | 30 +++++++++----------
>  tools/testing/selftests/mm/hugetlb-madvise.c  |  5 +---
>  tools/testing/selftests/mm/migration.c        | 13 ++++----
>  tools/testing/selftests/mm/pagemap_ioctl.c    |  4 +--
>  .../selftests/mm/split_huge_page_test.c       |  4 +--
>  5 files changed, 24 insertions(+), 32 deletions(-)

The patch forgot to move the FORCE_READ definition into a header?