Re: [PATCH v3 00/10] mm: thp: always enable mTHP support

Lance Yang
2026-04-09T08:30:08Z

+Cc THP

Some folks seem to be missing from CC for this series. Please run
scripts/get_maintainer.pl; it's your friend :)

Thanks,
Lance

On Wed, Apr 08, 2026 at 04:22:55PM -0400, 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. 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.
>
>Thanks to David Hildenbrand for suggesting this improvement and for
>providing guidance (all bugs and misconceptions are mine).
>
>This applies to Linus tree bfe62a454542 ("Merge tag 'soc-fixes-7.0-2'
>of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc").
>
>v3
>--
>
>- Rebased on top of latest Linus tree
>- Removed i915 patch as driver dropped has_transparent_hugepage() usage
>- Moved init_arch_has_pmd_leaves() call in start_kernel() to avoid conflict
> with early_param handlers clearing CPU feature flags
>- Fixed build error with CONFIG_MMU=n (kernel test robot)
>- Fixed huge_anon_orders_inherit default setting when !pgtable_pmd_leaves() (Baolin)
>- Small commit changelog improvements
>
>v2
>--
>- Added support for always enabling mTHPs for shmem (Baolin)
>- Improved commits changelog & added reviewed-by
>
>v1
>--
>- Call init_arch_has_pmd_leaves() from start_kernel()
>- Keep pgtable_has_pmd_leaves() calls tied to CONFIG_TRANSPARENT_HUGEPAGE (David)
>- Clear PUD_ORDER when clearing PMD_ORDER (David)
>- Small changelog improvements (David)
>- Rebased on top of latest mm-new
>
>Luiz Capitulino (10):
> docs: tmpfs: remove implementation detail reference
> mm: introduce pgtable_has_pmd_leaves()
> drivers: dax: use pgtable_has_pmd_leaves()
> drivers: nvdimm: use pgtable_has_pmd_leaves()
> mm: debug_vm_pgtable: use pgtable_has_pmd_leaves()
> mm: shmem: drop has_transparent_hugepage() usage
> 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 +-
> drivers/nvdimm/pfn_devs.c | 6 ++++--
> include/linux/huge_mm.h | 7 -------
> include/linux/pgtable.h | 19 ++++++++++++++++--
> init/main.c | 1 +
> mm/debug_vm_pgtable.c | 20 +++++++++----------
> mm/huge_memory.c | 15 +++++++-------
> mm/memory.c | 10 +++++++++-
> mm/shmem.c | 11 +++++-----
> 20 files changed, 80 insertions(+), 60 deletions(-)
>
>--
>2.53.0
>
>