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

[David Hildenbrand]

On 17.07.25 12:48, wang lian wrote:
> > On Wed, 16 Jul 2025 20:31:26 +0800 wang lian <lianux.mm@xxxxxxxxx> 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?
>
> Hi Andrew,
> You are absolutely right. My apologies for the inconvenience.
> This patch was sent standalone based on a suggestion from David during
> the discussion of a previous, larger patch series. In that original series,
> I had already moved the FORCE_READ() macro definition into vm_util.h.
>
> You can find the original patch series and discussion at this link:
> https://lore.kernel.org/lkml/20250714130009.14581-1-lianux.mm@xxxxxxxxx/
> It should also be in your mailing list archive.
>
> To make this easier to review and apply, I can send a new, small patch series
> that first introduces the FORCE_READ() macro in vm_util.h and then applies this refactoring.

Please simply perform the move of FORCE_READ() in this very patch where 
you also use it elswehere.

I missed that when skimming over this patch.

--
Cheers,

David / dhildenb