Sorry I didn't say at the time - thanks, I do plan to look through this at
some point :)
Cheers, Lorenzo
On Thu, Nov 06, 2025 at 04:28:47PM -0500, Luiz Capitulino wrote:
> Today, if an architecture implements has_transparent_hugepage() and the CPU
> lacks support for PMD-sized pages, the THP code disables all THP, including
> mTHP support. In addition, the kernel lacks a well defined API to check for
> PMD-sized page support. It currently relies on has_transparent_hugepage()
> and thp_disabled_by_hw(), but they are not well defined and are tied to
> THP support.
>
> This series addresses both issues by introducing a new well defined API
> to query PMD-sized page support: pgtable_has_pmd_leaves(). Using this
> new helper, we ensure that mTHP remains enabled even when the
> architecture or CPU doesn't support PMD-sized pages.
>
> An important detail is that we need to do the same refactoring for
> has_transparent_pud_hugepage(). I actually have patches for this one
> too, I'm not including them here because I want to get some initial
> feedback on the general approach first (and maybe it's better to
> do that in a separate series).
>
> Thanks to David Hildenbrand for suggesting this improvement and for
> providing guidance (all bugs and misconcentpions are mine).
>
> Luiz Capitulino (10):
> docs: tmpfs: remove implementation detail reference
> mm: introduce pgtable_has_pmd_leaves()
> drivers: dax: use pgtable_has_pmd_leaves()
> drivers: i915 selftest: use pgtable_has_pmd_leaves()
> drivers: nvdimm: use pgtable_has_pmd_leaves()
> mm: debug_vm_pgtable: use pgtable_has_pmd_leaves()
> treewide: rename has_transparent_hugepage() to arch_has_pmd_leaves()
> mm: replace thp_disabled_by_hw() with pgtable_has_pmd_leaves()
> mm: thp: always enable mTHP support
> mm: thp: x86: cleanup PSE feature bit usage
>
> Documentation/filesystems/tmpfs.rst | 5 ++---
> arch/mips/include/asm/pgtable.h | 4 ++--
> arch/mips/mm/tlb-r4k.c | 4 ++--
> arch/powerpc/include/asm/book3s/64/hash-4k.h | 2 +-
> arch/powerpc/include/asm/book3s/64/hash-64k.h | 2 +-
> arch/powerpc/include/asm/book3s/64/pgtable.h | 10 +++++-----
> arch/powerpc/include/asm/book3s/64/radix.h | 2 +-
> arch/powerpc/mm/book3s64/hash_pgtable.c | 4 ++--
> arch/s390/include/asm/pgtable.h | 4 ++--
> arch/x86/include/asm/pgtable.h | 6 ------
> arch/x86/include/asm/pgtable_32.h | 6 ++++++
> drivers/dax/dax-private.h | 2 +-
> .../gpu/drm/i915/gem/selftests/huge_pages.c | 2 +-
> drivers/nvdimm/pfn_devs.c | 4 ++--
> include/linux/huge_mm.h | 7 -------
> include/linux/pgtable.h | 14 +++++++++++--
> mm/debug_vm_pgtable.c | 20 +++++++++----------
> mm/huge_memory.c | 13 ++++++------
> mm/memory.c | 12 ++++++++++-
> mm/shmem.c | 8 ++++----
> 20 files changed, 72 insertions(+), 59 deletions(-)
>
> --
> 2.51.1
>