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b=UzH3ox9Y0nOATaoFSAUfpmTnl0wsXCNwRurs9V+s1qVATfkflVVi+w9vI81EGIIJD GeBaYA5W++V5Jcsaz/W+v+ZPnUEDx2A3++nIX4mUMFfhAtG33EXZKYOtXRgzeB0h82 Fh7uigv13xpa4J4mZBHTf+t/3sY9cIKmBxlw5QeKXvzRIhniKwQgOnYCMyo9KNgkl3 frJKuHsrJZhjmSdYc9B/VZgPTp1Log8ljJiKcds/RuvAIyBJ8zamt3DZlyV2VvQCqB RuwPmZddSJswiSE5QnBWMUkf9A5no4Y9QNXi0SsjJAPzC0ILZcWj92e3OKrBpvXake oL5Rz3XUzaHtw== Date: Thu, 14 May 2026 07:35:01 +0100 From: Lorenzo Stoakes To: Luiz Capitulino Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev, corbet@lwn.net, tsbogend@alpha.franken.de, maddy@linux.ibm.com, mpe@ellerman.id.au, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, x86@kernel.org, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org Subject: Re: [PATCH v4 0/9] mm: thp: always enable mTHP support Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 653C71A0002 X-Stat-Signature: 4jue85iwww6133kixm1btib9pkwdukn5 X-Rspam-User: X-HE-Tag: 1778740505-69135 X-HE-Meta: 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 KBplKsIQ cybRK71DmkfX0n78hyJC3d3veR6XjM70ACsXb5dfGKXFY0rbwr8KvexFLjxa5SF6wEflbeNaM2CaJOmqsTqDbEUKzJmVNAN/tLCLMANsbk/NnvpA+cv8s5dJpDgqdZmspM5jF8D9xhkJFYaSAdb7R7o4muIFgHzpwJ9JlKkdTssRUA7/0EptRhMR35eGU1EvMT3yRMnIIgmtSzHPZHecXx6xzviDlJzJJMcZNYxfMg+yHniY439BynEOO0spvaq5JEkkZoJtEqcG04N8yHBWXPltYrqS8CFuyod/N2xJkUU93Few= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: -cc my previous kernel mail (Minor annoying reminder to update my email to ljs@kernel.org :P) On Fri, May 01, 2026 at 03:18:42PM -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 08d0d3466664 ("Merge tag 'net-7.1-rc2' > of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net") > > NOTE: I used Claude Code Opus 4.6 to *review* the series before > posting. It did find one issue where a pgtable_has_pmd_leaves() > check was missing when assining huge_shmem_orders_inherit in > shmem_init(). > > v4 > -- > - Use static key for pgtable_has_pmd_leaves() API (Lance) > - Moved shmem pgtable_has_pmd_leaves() check to > shmem_allowable_huge_orders() (Baolin) > - Default pgtable_has_pmd_leaves() implementation to > IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE) (Zi) > - Dropped patch “mm: thp: x86: cleanup PSE feature bit usage” (Dave) > > 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 (9): > 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: introduce arch_has_pmd_leaves() > mm: replace thp_disabled_by_hw() with pgtable_has_pmd_leaves() > mm: thp: always enable mTHP support > > 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 | 4 +-- > 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 | 25 +++++++++++++------ > mm/memory.c | 11 +++++++- > mm/shmem.c | 21 +++++++++------- > 19 files changed, 93 insertions(+), 60 deletions(-) > > -- > 2.53.0 >