{"id":2229396,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2229396/?format=json","web_url":"http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260428081855.1249045-5-songmuchun@bytedance.com/","project":{"id":2,"url":"http://patchwork.ozlabs.org/api/1.1/projects/2/?format=json","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/"},"msgid":"<20260428081855.1249045-5-songmuchun@bytedance.com>","date":"2026-04-28T08:18:53","name":"[v8,4/6] mm/sparse-vmemmap: Fix DAX vmemmap accounting with optimization","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"87369a09430a64bd5dd87674bd8bb90c6e338d50","submitter":{"id":78930,"url":"http://patchwork.ozlabs.org/api/1.1/people/78930/?format=json","name":"Muchun Song","email":"songmuchun@bytedance.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260428081855.1249045-5-songmuchun@bytedance.com/mbox/","series":[{"id":501789,"url":"http://patchwork.ozlabs.org/api/1.1/series/501789/?format=json","web_url":"http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=501789","date":"2026-04-28T08:18:50","name":"[v8,1/6] mm/sparse-vmemmap: Fix vmemmap accounting underflow","version":8,"mbox":"http://patchwork.ozlabs.org/series/501789/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2229396/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2229396/checks/","tags":{},"headers":{"Return-Path":"\n ","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=kbarLWTO;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; 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Howlett\" ,\n\tVlastimil Babka ,\n\tMike Rapoport ,\n\tSuren Baghdasaryan ,\n\tMichal Hocko ,\n\tNicholas Piggin ,\n\tChristophe Leroy ,\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 ,\n\tstable@vger.kernel.org","Subject":"[PATCH v8 4/6] mm/sparse-vmemmap: Fix DAX vmemmap accounting with\n optimization","Date":"Tue, 28 Apr 2026 16:18:53 +0800","Message-Id":"<20260428081855.1249045-5-songmuchun@bytedance.com>","X-Mailer":"git-send-email 2.20.1","In-Reply-To":"<20260428081855.1249045-1-songmuchun@bytedance.com>","References":"<20260428081855.1249045-1-songmuchun@bytedance.com>","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","List-Unsubscribe":"","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_nr_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\")\nCc: stable@vger.kernel.org\nSigned-off-by: Muchun Song \nAcked-by: Mike Rapoport (Microsoft) \nAcked-by: Oscar Salvador \nAcked-by: David Hildenbrand (Arm) \n---\nv7-v8:\n- Move VM_WARN_ON_ONCE(nr_pages > PAGES_PER_SECTION); to the top of\n section_nr_vmemmap_pages().\n- Add Acked-by from David.\n---\n mm/sparse-vmemmap.c | 34 ++++++++++++++++++++++++++++++----\n 1 file changed, 30 insertions(+), 4 deletions(-)","diff":"diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c\nindex 3340f6d30b01..932082296e8d 100644\n--- a/mm/sparse-vmemmap.c\n+++ b/mm/sparse-vmemmap.c\n@@ -652,6 +652,31 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)\n \t}\n }\n \n+static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,\n+\t\tstruct vmem_altmap *altmap, struct dev_pagemap *pgmap)\n+{\n+\tconst unsigned int order = pgmap ? pgmap->vmemmap_shift : 0;\n+\tconst unsigned long pages_per_compound = 1UL << order;\n+\n+\tVM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SUBSECTION));\n+\tVM_WARN_ON_ONCE(nr_pages > PAGES_PER_SECTION);\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\tVM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, pages_per_compound));\n+\t\treturn VMEMMAP_RESERVE_NR * nr_pages / pages_per_compound;\n+\t}\n+\n+\tVM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION));\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 +684,7 @@ 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_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap));\n \n \treturn page;\n }\n@@ -670,7 +695,7 @@ 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_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap));\n \tvmemmap_free(start, end, altmap);\n }\n \n@@ -678,9 +703,10 @@ static void free_map_bootmem(struct page *memmap)\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_nr_vmemmap_pages(pfn, PAGES_PER_SECTION,\n+\t\t\t\t\t\t\tNULL, NULL));\n \tvmemmap_free(start, end, NULL);\n }\n \n","prefixes":["v8","4/6"]}