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Fri, 01 May 2026 15:19:59 -0400 X-MC-Unique: gWRvNscCP3GXc_lH56B9Qg-1 X-Mimecast-MFC-AGG-ID: gWRvNscCP3GXc_lH56B9Qg_1777663197 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 164D119560B7; Fri, 1 May 2026 19:19:56 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.64.126]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0A64C1801481; Fri, 1 May 2026 19:19:51 +0000 (UTC) From: Luiz Capitulino To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev Cc: 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, lorenzo.stoakes@oracle.com Subject: [PATCH v4 0/9] mm: thp: always enable mTHP support Date: Fri, 1 May 2026 15:18:42 -0400 Message-ID: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Mimecast-MFC-PROC-ID: DYFvueZNCXTI6eQsRSE-FkBNp_Hud0ChYph_QqgXAhU_1777663197 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 26C3F1A0015 X-Stat-Signature: xzd9xcxsst5axk1jsyk3yctsx1grgibe X-HE-Tag: 1777663205-881585 X-HE-Meta: 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 udhaxk+Z H/YYX86VJBEl0ZmCprJGrIZ1Ya1l+6I73Rc8bh5fLS4f0YznVd/2BuaiMvaaMXALS5nP3F9aSdqqZyatvaKHqhNbh2Q5nrJWNl1lwpqmZRphzEpDnBUc5pbxVemLPS4MEhUoV+0HyUwYy/8/WTk0iu9hOKT+pXxAOndOCEwHFq0Gwu3AKVytglmIDJ7hw1dVO+natp26ERExSoVWQQVoslAM5lq3HK6PB0kRY6Pn26HHA9YJmUrfFn2Wl62bmDKEqC3XzIqdNu0HEXvU/CO+7LEajzMRtOAqKcLZ3XqdcOSHymiYEw06ySr+hyAx4ruMdr5fw5Cwc/umdhY1BHnF1BN+GvKP4MZAKTX+i4hDB81cxMrs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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