Re: [PATCH v4 2/9] mm: introduce pgtable_has_pmd_leaves()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 5/1/26 21:18, Luiz Capitulino wrote:
> Currently, we have two helpers that check for PMD-sized pages but have
> different names and slightly different semantics:
> 
> - has_transparent_hugepage(): the name suggests it checks if THP is
>   enabled, but when CONFIG_TRANSPARENT_HUGEPAGE=y and the architecture
>   implements this helper, it actually checks if the CPU supports
>   PMD-sized pages
> 
> - thp_disabled_by_hw(): the name suggests it checks if THP is disabled
>   by the hardware, but it just returns a cached value acquired with
>   has_transparent_hugepage(). This helper is used in fast paths
> 
> This commit introduces a new helper called pgtable_has_pmd_leaves()
> which is intended to replace both has_transparent_hugepage() and
> thp_disabled_by_hw(). pgtable_has_pmd_leaves() has very clear semantics:
> it returns true if the CPU supports PMD-sized pages and false otherwise.
> It always returns a cached value, so it can be used in fast paths.

Oh, one more thing: what will be the semantics regarding
CONFIG_TRANSPARENT_HUGEPAGE?

I assume it will only return true if CONFIG_TRANSPARENT_HUGEPAGE is enabled,
correct?

That is, for example, relevant for patch #2.

We could later change these semantics, but for now we should be very clear about
what it means.

-- 
Cheers,

David