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GET /api/patches/2225416/?format=api
{ "id": 2225416, "url": "http://patchwork.ozlabs.org/api/patches/2225416/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260421022044.1217503-4-songmuchun@bytedance.com/", "project": { "id": 2, "url": "http://patchwork.ozlabs.org/api/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": "<20260421022044.1217503-4-songmuchun@bytedance.com>", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/20260421022044.1217503-4-songmuchun@bytedance.com/", "date": "2026-04-21T02:20:43", "name": "[v3,3/4] mm/sparse-vmemmap: Fix DAX vmemmap accounting with optimization", "commit_ref": null, "pull_url": null, "state": "handled-elsewhere", "archived": false, "hash": "174c4eeb4a02ae8e4323adb4cf056d6c17c95c62", "submitter": { "id": 78930, "url": "http://patchwork.ozlabs.org/api/people/78930/?format=api", "name": "Muchun Song", "email": "songmuchun@bytedance.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260421022044.1217503-4-songmuchun@bytedance.com/mbox/", "series": [ { "id": 500709, "url": "http://patchwork.ozlabs.org/api/series/500709/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=500709", "date": "2026-04-21T02:20:40", "name": "mm: Fix vmemmap optimization accounting and initialization", "version": 3, "mbox": "http://patchwork.ozlabs.org/series/500709/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2225416/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2225416/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <linuxppc-dev+bounces-19860-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=QGR7md10;\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\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", "Subject": "[PATCH v3 3/4] mm/sparse-vmemmap: Fix DAX vmemmap accounting with\n optimization", "Date": "Tue, 21 Apr 2026 10:20:43 +0800", "Message-Id": "<20260421022044.1217503-4-songmuchun@bytedance.com>", "X-Mailer": "git-send-email 2.20.1", "In-Reply-To": "<20260421022044.1217503-1-songmuchun@bytedance.com>", "References": "<20260421022044.1217503-1-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": "When vmemmap optimization is enabled for DAX, the nr_memmap_pages\ncounter in /proc/vmstat is incorrect. The current code always accounts\nfor the full, non-optimized vmemmap size, but vmemmap optimization\nreduces the actual number of vmemmap pages by reusing tail pages. This\ncauses the system to overcount vmemmap usage, leading to inaccurate\npage statistics in /proc/vmstat.\n\nFix this by introducing section_vmemmap_pages(), which returns the exact\nvmemmap page count for a given pfn range based on whether optimization\nis in effect.\n\nFixes: 15995a352474 (\"mm: report per-page metadata information\")\nSigned-off-by: Muchun Song <songmuchun@bytedance.com>\nAcked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>\n---\n mm/sparse-vmemmap.c | 32 ++++++++++++++++++++++++++++----\n 1 file changed, 28 insertions(+), 4 deletions(-)", "diff": "diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c\nindex 40290fbc1db4..05e3e2b94e32 100644\n--- a/mm/sparse-vmemmap.c\n+++ b/mm/sparse-vmemmap.c\n@@ -652,6 +652,29 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)\n \t}\n }\n \n+static int __meminit section_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,\n+\t\t\t\t\t struct vmem_altmap *altmap,\n+\t\t\t\t\t struct dev_pagemap *pgmap)\n+{\n+\tunsigned int order = pgmap ? pgmap->vmemmap_shift : 0;\n+\tunsigned long pages_per_compound = 1L << order;\n+\n+\tVM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, min(pages_per_compound,\n+\t\t\t\t\t\t\tPAGES_PER_SECTION)));\n+\tVM_WARN_ON_ONCE(pfn_to_section_nr(pfn) != pfn_to_section_nr(pfn + nr_pages - 1));\n+\n+\tif (!vmemmap_can_optimize(altmap, pgmap))\n+\t\treturn DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE);\n+\n+\tif (order < PFN_SECTION_SHIFT)\n+\t\treturn VMEMMAP_RESERVE_NR * nr_pages / pages_per_compound;\n+\n+\tif (IS_ALIGNED(pfn, pages_per_compound))\n+\t\treturn VMEMMAP_RESERVE_NR;\n+\n+\treturn 0;\n+}\n+\n static struct page * __meminit populate_section_memmap(unsigned long pfn,\n \t\tunsigned long nr_pages, int nid, struct vmem_altmap *altmap,\n \t\tstruct dev_pagemap *pgmap)\n@@ -659,7 +682,7 @@ static struct page * __meminit populate_section_memmap(unsigned long pfn,\n \tstruct page *page = __populate_section_memmap(pfn, nr_pages, nid, altmap,\n \t\t\t\t\t\t pgmap);\n \n-\tmemmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE));\n+\tmemmap_pages_add(section_vmemmap_pages(pfn, nr_pages, altmap, pgmap));\n \n \treturn page;\n }\n@@ -670,7 +693,7 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,\n \tunsigned long start = (unsigned long) pfn_to_page(pfn);\n \tunsigned long end = start + nr_pages * sizeof(struct page);\n \n-\tmemmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)));\n+\tmemmap_pages_add(-section_vmemmap_pages(pfn, nr_pages, altmap, pgmap));\n \tvmemmap_free(start, end, altmap);\n }\n \n@@ -679,9 +702,10 @@ static void free_map_bootmem(struct page *memmap, struct vmem_altmap *altmap,\n {\n \tunsigned long start = (unsigned long)memmap;\n \tunsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);\n+\tunsigned long pfn = page_to_pfn(memmap);\n \n-\tmemmap_boot_pages_add(-1L * (DIV_ROUND_UP(PAGES_PER_SECTION * sizeof(struct page),\n-\t\t\t\t\t\t PAGE_SIZE)));\n+\tmemmap_boot_pages_add(-section_vmemmap_pages(pfn, PAGES_PER_SECTION,\n+\t\t\t\t\t\t altmap, pgmap));\n \tvmemmap_free(start, end, NULL);\n }\n \n", "prefixes": [ "v3", "3/4" ] }