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GET /api/1.2/patches/2219967/?format=api
{ "id": 2219967, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2219967/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260405125240.2558577-43-songmuchun@bytedance.com/", "project": { "id": 2, "url": "http://patchwork.ozlabs.org/api/1.2/projects/2/?format=api", "name": "Linux PPC development", "link_name": "linuxppc-dev", "list_id": "linuxppc-dev.lists.ozlabs.org", "list_email": "linuxppc-dev@lists.ozlabs.org", "web_url": "https://github.com/linuxppc/wiki/wiki", "scm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git", "webscm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/", "list_archive_url_format": "https://lore.kernel.org/linuxppc-dev/{}/", "commit_url_format": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id={}" }, "msgid": "<20260405125240.2558577-43-songmuchun@bytedance.com>", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/20260405125240.2558577-43-songmuchun@bytedance.com/", "date": "2026-04-05T12:52:33", "name": "[42/49] mm/sparse-vmemmap: introduce section_vmemmap_page_structs()", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "95555a2148f2830b1dff582099b8068ed29c7061", "submitter": { "id": 78930, "url": "http://patchwork.ozlabs.org/api/1.2/people/78930/?format=api", "name": "Muchun Song", "email": "songmuchun@bytedance.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260405125240.2558577-43-songmuchun@bytedance.com/mbox/", "series": [ { "id": 498783, "url": "http://patchwork.ozlabs.org/api/1.2/series/498783/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=498783", "date": "2026-04-05T12:51:51", "name": "mm: Generalize vmemmap optimization for DAX and HugeTLB", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/498783/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2219967/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2219967/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <linuxppc-dev+bounces-19372-incoming=patchwork.ozlabs.org@lists.ozlabs.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linuxppc-dev@lists.ozlabs.org" ], "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=bytedance.com header.i=@bytedance.com\n header.a=rsa-sha256 header.s=google header.b=AJI2KW/L;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; 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Howlett\" <Liam.Howlett@oracle.com>,\n\tVlastimil Babka <vbabka@kernel.org>,\n\tMike Rapoport <rppt@kernel.org>,\n\tSuren Baghdasaryan <surenb@google.com>,\n\tMichal Hocko <mhocko@suse.com>,\n\tNicholas Piggin <npiggin@gmail.com>,\n\tChristophe Leroy <chleroy@kernel.org>,\n\taneesh.kumar@linux.ibm.com,\n\tjoao.m.martins@oracle.com,\n\tlinux-mm@kvack.org,\n\tlinuxppc-dev@lists.ozlabs.org,\n\tlinux-kernel@vger.kernel.org,\n\tMuchun Song <songmuchun@bytedance.com>", "Subject": "[PATCH 42/49] mm/sparse-vmemmap: introduce\n section_vmemmap_page_structs()", "Date": "Sun, 5 Apr 2026 20:52:33 +0800", "Message-Id": "<20260405125240.2558577-43-songmuchun@bytedance.com>", "X-Mailer": "git-send-email 2.20.1", "In-Reply-To": "<20260405125240.2558577-1-songmuchun@bytedance.com>", "References": "<20260405125240.2558577-1-songmuchun@bytedance.com>", "X-Mailing-List": "linuxppc-dev@lists.ozlabs.org", "List-Id": "<linuxppc-dev.lists.ozlabs.org>", "List-Help": "<mailto:linuxppc-dev+help@lists.ozlabs.org>", "List-Owner": "<mailto:linuxppc-dev+owner@lists.ozlabs.org>", "List-Post": "<mailto:linuxppc-dev@lists.ozlabs.org>", "List-Archive": "<https://lore.kernel.org/linuxppc-dev/>,\n <https://lists.ozlabs.org/pipermail/linuxppc-dev/>", "List-Subscribe": "<mailto:linuxppc-dev+subscribe@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-digest@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-nomail@lists.ozlabs.org>", "List-Unsubscribe": "<mailto:linuxppc-dev+unsubscribe@lists.ozlabs.org>", "Precedence": "list", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-Spam-Status": "No, score=-0.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID,\n\tDKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS\n\tautolearn=disabled version=4.0.1 OzLabs 8", "X-Spam-Checker-Version": "SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org" }, "content": "The function compound_nr_pages() in mm_init.c was introduced to determine\nhow many unique struct pages need to be initialized when vmemmap optimization\nis enabled. However, it exposes sparse_vmemmap internals to mm_init.c.\n\nNow that DAX and HugeTLB vmemmap optimizations are unified and simplified,\nwe can expose a cleaner API from sparse.c to calculate the exact number\nof struct page structures needed.\n\nIntroduce section_vmemmap_page_structs() which returns the number of\npage structs that require initialization, rather than the number of physical\nvmemmap pages to allocate. This perfectly aligns with the requirements\nof memmap_init_zone_device().\n\nAs a result:\n1. compound_nr_pages() is removed entirely.\n2. The internal section_vmemmap_pages() in sparse.c is rewritten as\n a simple wrapper that calculates the number of physical pages based\n on section_vmemmap_page_structs().\n3. A restrictive VM_BUG_ON spanning sections is removed, safely allowing\n compound pages (like 1G DAX pages) to cross section boundaries during\n device memory initialization.\n\nSigned-off-by: Muchun Song <songmuchun@bytedance.com>\n---\n mm/internal.h | 8 +++++++-\n mm/mm_init.c | 21 +--------------------\n mm/sparse.c | 9 ++++-----\n 3 files changed, 12 insertions(+), 26 deletions(-)", "diff": "diff --git a/mm/internal.h b/mm/internal.h\nindex 7f0731e5c84f..02064f21bfe1 100644\n--- a/mm/internal.h\n+++ b/mm/internal.h\n@@ -998,7 +998,13 @@ static inline void __section_mark_present(struct mem_section *ms,\n \tms->section_mem_map |= SECTION_MARKED_PRESENT;\n }\n \n-int section_vmemmap_pages(unsigned long pfn, unsigned long nr_pages);\n+int section_vmemmap_page_structs(unsigned long pfn, unsigned long nr_pages);\n+\n+static inline int section_vmemmap_pages(unsigned long pfn, unsigned long nr_pages)\n+{\n+\treturn DIV_ROUND_UP(section_vmemmap_page_structs(pfn, nr_pages) *\n+\t\t\t sizeof(struct page), PAGE_SIZE);\n+}\n #else\n static inline void memblocks_present(void) {}\n static inline void sparse_init(void) {}\ndiff --git a/mm/mm_init.c b/mm/mm_init.c\nindex 6b23b5f02544..74ccc556bf6e 100644\n--- a/mm/mm_init.c\n+++ b/mm/mm_init.c\n@@ -1060,24 +1060,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,\n \t}\n }\n \n-/*\n- * With compound page geometry and when struct pages are stored in ram most\n- * tail pages are reused. Consequently, the amount of unique struct pages to\n- * initialize is a lot smaller that the total amount of struct pages being\n- * mapped. This is a paired / mild layering violation with explicit knowledge\n- * of how the sparse_vmemmap internals handle compound pages in the lack\n- * of an altmap.\n- */\n-static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,\n-\t\t\t\t\t struct dev_pagemap *pgmap,\n-\t\t\t\t\t const struct mem_section *ms)\n-{\n-\tif (!section_vmemmap_optimizable(ms))\n-\t\treturn pgmap_vmemmap_nr(pgmap);\n-\n-\treturn VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page));\n-}\n-\n static void __ref memmap_init_compound(struct page *head,\n \t\t\t\t unsigned long head_pfn,\n \t\t\t\t unsigned long zone_idx, int nid,\n@@ -1141,8 +1123,7 @@ void __ref memmap_init_zone_device(struct zone *zone,\n \t\t\tcontinue;\n \n \t\tmemmap_init_compound(page, pfn, zone_idx, nid, pgmap,\n-\t\t\t\t compound_nr_pages(altmap, pgmap,\n-\t\t\t\t\t\t __pfn_to_section(pfn)));\n+\t\t\t\t section_vmemmap_page_structs(pfn, pfns_per_compound));\n \t}\n \n \t/*\ndiff --git a/mm/sparse.c b/mm/sparse.c\nindex 163bb17bba96..400542302ad4 100644\n--- a/mm/sparse.c\n+++ b/mm/sparse.c\n@@ -345,23 +345,22 @@ static void __init sparse_usage_fini(void)\n \tsparse_usagebuf = sparse_usagebuf_end = NULL;\n }\n \n-int __meminit section_vmemmap_pages(unsigned long pfn, unsigned long nr_pages)\n+int __meminit section_vmemmap_page_structs(unsigned long pfn, unsigned long nr_pages)\n {\n \tconst struct mem_section *ms = __pfn_to_section(pfn);\n \tunsigned int order = section_order(ms);\n \tunsigned long pages_per_compound = 1L << order;\n \n \tVM_BUG_ON(!IS_ALIGNED(pfn | nr_pages, min(pages_per_compound, PAGES_PER_SECTION)));\n-\tVM_BUG_ON(pfn_to_section_nr(pfn) != pfn_to_section_nr(pfn + nr_pages - 1));\n \n \tif (!section_vmemmap_optimizable(ms))\n-\t\treturn DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE);\n+\t\treturn nr_pages;\n \n \tif (order < PFN_SECTION_SHIFT)\n-\t\treturn OPTIMIZED_FOLIO_VMEMMAP_PAGES * nr_pages / pages_per_compound;\n+\t\treturn OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS * nr_pages / pages_per_compound;\n \n \tif (IS_ALIGNED(pfn, pages_per_compound))\n-\t\treturn OPTIMIZED_FOLIO_VMEMMAP_PAGES;\n+\t\treturn OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS;\n \n \treturn 0;\n }\n", "prefixes": [ "42/49" ] }