From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F69A418A58 for ; Fri, 9 Oct 2026 05:59:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791525547; cv=none; b=en9TxjXqFI7YyFZi9e9069Vt/GyNj2g/N1C1quavkbrK4CnThSLe4NG9XgNANYt1kTtmmyHKiJkZni4nkmWjqKlsjaJEX1+R+q+7uqEe8NkXE27O4bCpQRWmcxuyPs4M4uZWMNgP8YXkJ6femYtcAOZC5uIZ0S5n0iD3p6AOuxw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791525547; c=relaxed/simple; bh=UdVyFL+l/OSlgGjcX+HnTw4FIFWzqZBOiTkVbTJB84M=; h=Date:To:From:Subject:Message-Id; b=cRyt2RO5pg+Wl0vkJ1TuHAP+KULKjgPtd1tuKOpi3GHV6ke+R49cyaBqo8o+sfh9y+jA0uzspOQF+teu+j0tEt/jM/OIPBW3+X2QWkhuyy4RFvdkBzqqhCBjPuZZbGj0zNvAW+G1NztGsx7OHqokkmToKiTFriVMnUuX4uOzopo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=1zA0Le9F; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="1zA0Le9F" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34D311F000FF; Fri, 9 Oct 2026 05:59:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791525546; bh=jZDGiG7jGMO1+LoMX50AnIiNIOxihQtD7ksL6yearOo=; h=Date:To:From:Subject; b=1zA0Le9FJmeS+1qj8Uh7WAQI903x+78XN5VmXwsVyYRrS0Kh+oSscuC1+ceeKWCrF ITrTu7ZgnYfOKT2nVS9FF8ttEDKxNo3DNwRSDl/Fae5+7UhyVmu1KhYgmYebqQTZ2A YWnsux1zSyPgDyqLYzbroptG0Z4+pSlvJEUSbynY= Date: Thu, 08 Oct 2026 22:59:05 -0700 To: mm-commits@vger.kernel.org,sshegde@linux.ibm.com,rppt@kernel.org,ritesh.list@gmail.com,rdunlap@infradead.org,qi.zheng@linux.dev,osalvador@suse.de,npiggin@gmail.com,mpe@ellerman.id.au,maddy@linux.ibm.com,ljs@kernel.org,lance.yang@linux.dev,david@kernel.org,corbet@lwn.net,chleroy@kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] documentation-mm-update-dax-vmemmap-deduplication-docs.patch removed from -mm tree Message-Id: <20261009055906.34D311F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: Documentation/mm: update DAX vmemmap deduplication docs has been removed from the -mm tree. Its filename was documentation-mm-update-dax-vmemmap-deduplication-docs.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Muchun Song Subject: Documentation/mm: update DAX vmemmap deduplication docs Date: Wed, 30 Sep 2026 22:06:27 +0800 Device DAX now uses the common per-zone shared tail page for vmemmap deduplication. The old documentation still described a DAX-specific layout with a separately populated tail vmemmap page and half the HugeTLB savings. Update the generic and powerpc documentation to describe the shared layout. In the powerpc document, keep the radix and 64K-specific details, drop the duplicated 4K PUD arithmetic, and replace the repeated device-dax diagrams with a single parameterized PMD/PUD diagram. Link: https://lore.kernel.org/20260930140627.57431-13-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Acked-by: Qi Zheng Acked-by: David Hildenbrand (Arm) Cc: Oscar Salvador Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Jonathan Corbet Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Nicholas Piggin Cc: Christophe Leroy Cc: Ritesh Harjani (IBM) Cc: Shrikanth Hegde Cc: Randy Dunlap Cc: Lance Yang --- Documentation/arch/powerpc/vmemmap_dedup.rst | 90 +++-------------- Documentation/mm/vmemmap_dedup.rst | 32 ------ 2 files changed, 21 insertions(+), 101 deletions(-) --- a/Documentation/arch/powerpc/vmemmap_dedup.rst~documentation-mm-update-dax-vmemmap-deduplication-docs +++ a/Documentation/arch/powerpc/vmemmap_dedup.rst @@ -19,82 +19,28 @@ With 1G PUD level mapping, we require 16 vmemmap page can contain 1024 struct pages (64K/sizeof(struct page)). Hence we require 16 64K pages in vmemmap to map the struct page for 1G PUD level mapping. -Here's how things look like on device-dax after the sections are populated:: - +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ - | | | 0 | -------------> | 0 | - | | +-----------+ +-----------+ - | | | 1 | -------------> | 1 | - | | +-----------+ +-----------+ - | | | 2 | ----------------^ ^ ^ ^ ^ ^ - | | +-----------+ | | | | | - | | | 3 | ------------------+ | | | | - | | +-----------+ | | | | - | | | 4 | --------------------+ | | | - | PUD | +-----------+ | | | - | level | | . | ----------------------+ | | - | mapping | +-----------+ | | - | | | . | ------------------------+ | - | | +-----------+ | - | | | 15 | --------------------------+ - | | +-----------+ - | | - | | - | | - +-----------+ - - With 4K page size, 2M PMD level mapping requires 512 struct pages and a single 4K vmemmap page contains 64 struct pages(4K/sizeof(struct page)). Hence we require 8 4K pages in vmemmap to map the struct page for 2M pmd level mapping. -Here's how things look like on device-dax after the sections are populated:: - - +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ - | | | 0 | -------------> | 0 | - | | +-----------+ +-----------+ - | | | 1 | -------------> | 1 | - | | +-----------+ +-----------+ - | | | 2 | ----------------^ ^ ^ ^ ^ ^ - | | +-----------+ | | | | | - | | | 3 | ------------------+ | | | | - | | +-----------+ | | | | - | | | 4 | --------------------+ | | | - | PMD | +-----------+ | | | - | level | | 5 | ----------------------+ | | - | mapping | +-----------+ | | - | | | 6 | ------------------------+ | - | | +-----------+ | - | | | 7 | --------------------------+ - | | +-----------+ - | | - | | - | | - +-----------+ - -With 1G PUD level mapping, we require 262144 struct pages and a single 4K -vmemmap page can contain 64 struct pages (4K/sizeof(struct page)). Hence we -require 4096 4K pages in vmemmap to map the struct pages for 1G PUD level -mapping. - -Here's how things look like on device-dax after the sections are populated:: - - +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ - | | | 0 | -------------> | 0 | - | | +-----------+ +-----------+ - | | | 1 | -------------> | 1 | - | | +-----------+ +-----------+ - | | | 2 | ----------------^ ^ ^ ^ ^ ^ - | | +-----------+ | | | | | - | | | 3 | ------------------+ | | | | - | | +-----------+ | | | | - | | | 4 | --------------------+ | | | - | PUD | +-----------+ | | | - | level | | . | ----------------------+ | | - | mapping | +-----------+ | | - | | | . | ------------------------+ | - | | +-----------+ | - | | | 4095 | --------------------------+ - | | +-----------+ +Here's how things look on device-dax after vmemmap-optimized sections are +populated. ``N`` is the number of vmemmap pages required by the DAX mapping +above:: + + Device DAX vmemmap pages (N pages) backing page frames + +-----------+ ---virt_to_page---> +-----------+ mapping to +-------------+ + | | | 0 | -------------> | 0 | + | | +-----------+ +-------------+ + | | | 1 | ------+ + | | +-----------+ | + | | | 2 | ------+ + | | +-----------+ | + | | | . | ------+ +-------------+ + | PMD/PUD | +-----------+ | | A single, | + | level | | . | ------+------> | per-zone | + | mapping | +-----------+ | | shared tail | + | | | N - 1 | ------+ | page | + | | +-----------+ +-------------+ | | | | | | --- a/Documentation/mm/vmemmap_dedup.rst~documentation-mm-update-dax-vmemmap-deduplication-docs +++ a/Documentation/mm/vmemmap_dedup.rst @@ -1,4 +1,3 @@ - .. SPDX-License-Identifier: GPL-2.0 ========================================= @@ -192,32 +191,7 @@ to 4 on HugeTLB pages. There's no remapping of vmemmap given that device-dax memory is not part of System RAM ranges initialized at boot. Thus the tail page deduplication -happens at a later stage when we populate the sections. HugeTLB reuses the -the head vmemmap page representing, whereas device-dax reuses the tail -vmemmap page. This results in only half of the savings compared to HugeTLB. - -Deduplicated tail pages are not mapped read-only. +happens at a later stage when we populate the sections. -Here's how things look like on device-dax after the sections are populated:: - - +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+ - | | | 0 | -------------> | 0 | - | | +-----------+ +-----------+ - | | | 1 | -------------> | 1 | - | | +-----------+ +-----------+ - | | | 2 | ----------------^ ^ ^ ^ ^ ^ - | | +-----------+ | | | | | - | | | 3 | ------------------+ | | | | - | | +-----------+ | | | | - | | | 4 | --------------------+ | | | - | PMD | +-----------+ | | | - | level | | 5 | ----------------------+ | | - | mapping | +-----------+ | | - | | | 6 | ------------------------+ | - | | +-----------+ | - | | | 7 | --------------------------+ - | | +-----------+ - | | - | | - | | - +-----------+ +Deduplicated tail pages are not mapped read-only. The mapping layout is the same +as HugeTLB. _ Patches currently in -mm which might be from muchun.song@linux.dev are mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch mm-mm_init-add-zone-mismatch-warning-during-page-init.patch