From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f45.google.com (mail-pj1-f45.google.com [209.85.216.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6626F38A70A for ; Fri, 11 Sep 2026 05:03:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789103013; cv=none; b=Q5lBrXVpytq8DBEQmLPnrsQfGq/wKqze5EbOqJPxhxhXbtjoj0/PAcnh48EX0mQo2+UibgkR18UBRPWjPat0Ywc+7XoAhzky7c6ROT2ODiK4PitU7VxZLCE02VkEJwIj5Ywe5qq45IjjdCNTH+1VdIVkJdOpqAtgbuSGOHUzG+A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789103013; c=relaxed/simple; bh=61T4yHtrc+/68Njc8a6Em4ai4R7Ll91D9PGAmdrjjxo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=hOULPEfLuLXfmccgqWMv0URaqYa7Qi0VVreXJmKNiZldaipV2WTFHCOFhM95tmNM7CvGJCC+RD/z0C+hAtIjTw6IJu7EB+YOgjvrRGAc2lg6DGnq9KeJ9LQlRnaHrUbAmAoeCazh0z0V7XSLc0AHQPNG+I8KCT4fbAJlJKt/TQA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=OItLOlIO; arc=none smtp.client-ip=209.85.216.45 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="OItLOlIO" Received: by mail-pj1-f45.google.com with SMTP id 98e67ed59e1d1-38dfe7eb825so488706a91.0 for ; Thu, 10 Sep 2026 22:03:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1789103007; x=1789707807; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to:content-type; bh=qqQtNE5K5bGF4fAhBmQKuNzeCVlz+kHVYANXwAzhHeA=; b=OItLOlIOXlUIS6A3VCFW7vJ3vP44BD2ixBXKW/3RTx6J3ruJyDaD8HqDZY912X2IdE mUw9rp3mqapwNm4w+oltQm/33ibredE0PnPIp4XEIldx0iZP4GAja/Y1/X6J8JOMZG5m iaFeSnologR2tP7PNCelvzULLYLWEVJZHkATdcce2qE3mZ7HYH0ifnZKI9jfqtH7X219 N2e8hkUoEtgYtoMMfRSIqGoJZQMtrv+5Y0g3D0PMspf6LokK1gO+XbQnL9KBQNy3hAyZ fJnVmwNYgjZKB4D7MjAJhOh+eNqrMmpO8l8lqMykh0vOEKC8eac14IFucH0xXbEh1Job XWOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789103007; x=1789707807; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=qqQtNE5K5bGF4fAhBmQKuNzeCVlz+kHVYANXwAzhHeA=; b=SFOs+rfWJrZ7AjVmHd3r+6dvYHscPJdSktmYUmd7GwwR1EoX+FkmEgjL2CuovYdQSa NYmxFfsC6AMXgC7nsIz5SoAM+wtFwo+qslUsQCDIljGyrz+YoD1dTUl4UQxd7PKFJXYg HbVr1h8wO1+iZUgF4nga1tLdH4jVrSKVxsqYkPxS7HOtmYd57nv9w5TP2S+0iP12zb5W YPLjP8tQhIhwP7VqMrxmHAq7ytpYHWjOsbWMWCxcj8hGIjCJ6616YZ2y5J19irGsDjyP kQbAR++dlQtO22FyBdvhumt1YCX2qonJBlrNqjXpu75La694EVYAa7ATSU8kE5Ugy9td fU/w== X-Forwarded-Encrypted: i=1; AKwUvBykvWDRUIXesus8Q4eOzjQH1rgdfHs3M2gK3gzASgOQcclJKQhIE48HzKvYIE0RpgXSD4gxhJDlS9k=@vger.kernel.org X-Gm-Message-State: AFuF++mAwIu32NJ2M4nrbSd9NfuJnjKjO0IcRxXbJHLe5ZsXDm4DCuWL TwkyNvYuTWWeRqKiaG6OEschoailvRNyyLox7jlffD6v5aQF0NePmY0dleI8hrAt9gc= X-Gm-Gg: AYBFou0qGrbnaG+LcmBF0CY8+1ftkGRPuq4VP5fNniMSbuki64W3+/wM+FoO8/KlXen r6Aw1d1GZI/axOmdMX5nfw65Enq3CZo2qr0VIqTeauoSfivf4HAIHIhFk7MAq3+fHrYJFxlyHoN gcyqdsEB5nZJ5gla/244B9q5h2Fo35vSo15bG/C/ovl3LMHfYQa+ysCvZLvQNi7YIissSXXCJDN ExYYm5IM41m3PAQ/T5AXDenrGy2mc1KXOnV9tFMNGO7TpKTAWeyaeIRGK6nPrbHIRolTseaHOlk ttE6yL6IogHn7bEL52CAoNcR3iE09+a0jiBXN/dlBhHVFS//OirwWa0Oqa3agRk1NgeolCotnzf wMiisPzcJc7bFmUqcO1sc0+DKYOp+ozDeJmjSxVHeFFx+Xt2WLUiGljz7NLzQ89ivXBEACuRkZi 9j/YRiPKSuVzBtoY04RqLzZ1a+B2gFJniUugQk9CPoYIz3BDUHIJJlk++pD/DLm2qRYtd40CACc /WJEkIFOSSewgk0/Y/SylYJjbdMGqRT3H+l X-Received: by 2002:a17:90b:1d45:b0:398:9be9:ab8f with SMTP id 98e67ed59e1d1-39d9c21cf40mr3843551a91.20.1789103006582; Thu, 10 Sep 2026 22:03:26 -0700 (PDT) Received: from G6L4RL2QG9.bytedance.net ([61.213.176.11]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39d99531b16sm2651561a91.14.2026.09.10.22.03.21 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 10 Sep 2026 22:03:25 -0700 (PDT) From: Muchun Song To: Andrew Morton , David Hildenbrand , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Randy Dunlap , Muchun Song Subject: [PATCH v3 00/11] mm: Switch device DAX to section-based vmemmap optimization Date: Fri, 11 Sep 2026 13:02:17 +0800 Message-ID: <20260911050228.58884-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This series is split out from the earlier, larger series "mm: Generalize HVO for HugeTLB and device DAX" [1]. While the parent series generalizes vmemmap optimization across HugeTLB and device DAX, this subset addresses a single, self-contained step: switching device DAX to the section-based sparse-vmemmap optimization infrastructure introduced for HugeTLB. After the HugeTLB conversion, optimized vmemmap state is described by the memory section and the sparse-vmemmap population path can allocate or reuse shared tail vmemmap pages based on that metadata. Device DAX still uses the older DAX-specific population model, including a separate tail vmemmap page reservation and architecture-specific logic to locate or populate reusable tail pages. This series makes device DAX use the same section-based model. Device DAX records the compound page order from pgmap->vmemmap_shift in section metadata before vmemmap population, uses the common per-zone shared tail vmemmap page, and drops the extra reserved tail page. The powerpc radix path is updated to use the same shared tail-page helper, so the generic and powerpc DAX paths follow the same reservation model. The first patches prepare the shared infrastructure by introducing a generic CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION symbol, factoring out shared tail-page allocation, and keeping the special shared-tail struct page initialization local to sparse-vmemmap. The middle patches move device DAX onto that infrastructure by recording the device DAX compound page order in memory-section metadata, using that metadata to back generic device DAX mappings with the common per-zone shared tail page, exposing the shared helpers so the powerpc radix path can use the same model, and dropping the extra DAX-only tail page reservation and the now-unused section accounting arguments. The final patch updates the documentation for the new DAX layout. This is intended to be the third smaller step toward the broader HVO generalization. The wider HVO consolidation between HugeTLB and device DAX is left for follow-up series. [1] https://lore.kernel.org/all/20260513130542.35604-1-songmuchun@bytedance.com/ v3: - Use EOPNOTSUPP for partial additions to sections that already use optimized vmemmap mappings - Move device_zone() after NODE_DATA() to fix non-NUMA builds - Collect Acked-by tags from David Hildenbrand and Qi Zheng - Rebase onto mm/mm-new v2: https://lore.kernel.org/all/20260908030335.96549-1-songmuchun@bytedance.com/ - Add a missing SPARSEMEM_VMEMMAP dependency (suggested by Qi Zheng, reported by Sashiko) - Add an explicit ZONE_DEVICE dependency for DEV_DAX - Add missing dependencies to the new public header - Explain why optimized and ordinary layouts cannot share a section (suggested by Qi Zheng) - Explain why sharing tail vmemmap pages is safe for DEV-DAX (suggested by Qi Zheng) - Clarify the removal of duplicated 4K PUD calculations from the docs (reported by Sashiko) - Collect Acked-by tags from Qi Zheng v1: https://lore.kernel.org/all/20260831075342.57563-1-songmuchun@bytedance.com/ Muchun Song (11): mm/sparse-vmemmap: introduce CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION mm/sparse-vmemmap: factor out shared vmemmap tail page allocation mm/sparse-vmemmap: open-code init_compound_tail() mm/sparse-vmemmap: prepare DAX vmemmap population for compound page orders mm/sparse-vmemmap: set compound page order for device DAX mm/sparse-vmemmap: switch device DAX to shared tail vmemmap pages mm/sparse-vmemmap: move vmemmap optimization helpers to a public header powerpc/mm: switch device DAX to shared tail vmemmap pages mm/sparse-vmemmap: drop the extra tail page from device DAX reservation mm/sparse-vmemmap: drop unused section_nr_vmemmap_pages() arguments Documentation/mm: update DAX vmemmap deduplication docs Documentation/arch/powerpc/vmemmap_dedup.rst | 90 ++------- Documentation/mm/vmemmap_dedup.rst | 32 +-- MAINTAINERS | 1 + arch/powerpc/mm/book3s64/radix_pgtable.c | 124 +----------- arch/x86/entry/vdso/vdso32/fake_32bit_build.h | 2 +- drivers/dax/Kconfig | 2 + fs/Kconfig | 1 + include/linux/mm.h | 6 +- include/linux/mmzone.h | 23 ++- include/linux/page-flags.h | 5 +- include/linux/vmemmap-optimization.h | 94 +++++++++ mm/Kconfig | 4 + mm/hugetlb.c | 2 +- mm/hugetlb_vmemmap.c | 30 +-- mm/internal.h | 9 - mm/memory_hotplug.c | 6 +- mm/mm_init.c | 17 +- mm/sparse-vmemmap.c | 184 ++++++++---------- mm/sparse.c | 3 +- mm/sparse.h | 81 +------- 20 files changed, 253 insertions(+), 463 deletions(-) create mode 100644 include/linux/vmemmap-optimization.h base-commit: c46036ca3ab7a7628fabe5790aefd917d0858db6 -- 2.54.0