Re: [PATCH v4 09/19] selftests/mm: add folio-order detection self-check

[Kiryl Shutsemau]

On Tue, Aug 18, 2026 at 11:30:06AM +0100, Lorenzo Stoakes (ARM) wrote:
> On Sat, Aug 15, 2026 at 02:58:51AM +0100, Kiryl Shutsemau wrote:
> > From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
> >
> > The khugepaged mTHP tests detect collapse results with the vm_util
> > folio-order helpers rather than smaps AnonHugePages, which only sees PMD
> > mappings.  If those helpers are wrong, every case built on them is wrong
> > the same way, and nothing says so.
> >
> > Check them directly.  For every anon THP order the kernel supports, fault
> > memory in with only that order enabled.  Require the helpers to classify
> > the backing as exactly that order: not a neighbouring order, and 4K-backed
> > memory as order 0.
> >
> > Run it in the thp category, ahead of ./khugepaged, so a broken helper is
> > reported as itself rather than as a collapse failure.  Verified on x86-64
> > 4K (orders 0, 2-9) and arm64 64K (orders 0, 2-13).
> >
> > The test needs ALIGN(), which hmm-tests.c and migration.c each defined
> > privately.  Move it to vm_util.h and drop both copies.
> 
> Also:
> 
> uffd-unit-tests defines ALIGN_UP()...
> 
> And really you probably want to match the kernel convention of ALIGN()
> defaulting to align-up (for some reason) and name this ALIGN_DOWN() to be
> consistent and avoid confusion BUT...

Hm? It is align-up:

#define ALIGN(x, a)                   (((x) + (a) - 1) & ~((a) - 1))

It matches kernel definition.

pkey-helpers.h has ALIGN_UP(), ALIGN_DOWN() and two pointer variants of
its own.  Folding those onto the vm_util.h one is worth doing, as a
follow-up rather than in this series.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov