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GET /api/1.2/patches/2219948/?format=api
{ "id": 2219948, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2219948/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20260405125240.2558577-24-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": "<20260405125240.2558577-24-songmuchun@bytedance.com>", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/20260405125240.2558577-24-songmuchun@bytedance.com/", "date": "2026-04-05T12:52:14", "name": "[23/49] mm/mm_init: skip initializing shared tail pages for compound pages", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "7765fcd4948ae782f874dc146a95a37726573786", "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/20260405125240.2558577-24-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/2219948/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2219948/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <linuxppc-dev+bounces-19353-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=E0L7jHIx;\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 23/49] mm/mm_init: skip initializing shared tail pages for\n compound pages", "Date": "Sun, 5 Apr 2026 20:52:14 +0800", "Message-Id": "<20260405125240.2558577-24-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": "Currently, memmap_init_range() unconditionally initializes all struct pages\nwithin a section. However, when HugeTLB Vmemmap Optimization (HVO) is enabled,\nshared vmemmap tail pages are allocated during the vmemmap population phase\n(e.g., via vmemmap_get_tail()). These shared tail pages are left intentionally\nuninitialized at that time because the subsequent memmap_init() would simply\noverwrite them.\n\nIf memmap_init_range() continues to initialize these shared tail pages, it\nwill overwrite the carefully constructed HVO mappings and metadata. This forces\nsubsystems like HugeTLB to implement workarounds (like re-initializing or\ncompensating for the overwritten data in their own init routines, as seen\nin hugetlb_vmemmap_init()).\n\nTherefore, the primary motivation of this patch is to prevent memmap_init_range()\nfrom incorrectly overwriting the shared vmemmap tail pages. By detecting if a\npage is an optimizable compound vmemmap page (using the newly introduced section\norder), we can safely skip its redundant initialization.\n\nAs a significant side-effect, skipping the initialization of these shared tail\npages also saves substantial CPU cycles during the early boot stage.\n\nSigned-off-by: Muchun Song <songmuchun@bytedance.com>\n---\n mm/internal.h | 11 +++++++++++\n mm/mm_init.c | 19 +++++++++++++++----\n 2 files changed, 26 insertions(+), 4 deletions(-)", "diff": "diff --git a/mm/internal.h b/mm/internal.h\nindex a8acabcd1d93..1060d7c07f5b 100644\n--- a/mm/internal.h\n+++ b/mm/internal.h\n@@ -1011,6 +1011,17 @@ static inline void sparse_init_subsection_map(void)\n }\n #endif /* CONFIG_SPARSEMEM_VMEMMAP */\n \n+static inline bool vmemmap_page_optimizable(const struct page *page)\n+{\n+\tunsigned long pfn = page_to_pfn(page);\n+\tunsigned int order = section_order(__pfn_to_section(pfn));\n+\n+\tif (!is_power_of_2(sizeof(struct page)))\n+\t\treturn false;\n+\n+\treturn (pfn & ((1L << order) - 1)) >= OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS;\n+}\n+\n #if defined CONFIG_COMPACTION || defined CONFIG_CMA\n \n /*\ndiff --git a/mm/mm_init.c b/mm/mm_init.c\nindex 977a837b7ef6..7f5b326e9298 100644\n--- a/mm/mm_init.c\n+++ b/mm/mm_init.c\n@@ -676,12 +676,13 @@ static inline void fixup_hashdist(void) {}\n \n static __meminit void pageblock_migratetype_init_range(unsigned long pfn,\n \t\t\t\t\t\t unsigned long nr_pages,\n-\t\t\t\t\t\t int migratetype)\n+\t\t\t\t\t\t int migratetype,\n+\t\t\t\t\t\t bool isolate)\n {\n \tunsigned long end = pfn + nr_pages;\n \n \tfor (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) {\n-\t\tinit_pageblock_migratetype(pfn_to_page(pfn), migratetype, false);\n+\t\tinit_pageblock_migratetype(pfn_to_page(pfn), migratetype, isolate);\n \t\tcond_resched();\n \t}\n }\n@@ -912,6 +913,16 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone\n \t\t}\n \n \t\tpage = pfn_to_page(pfn);\n+\t\tif (vmemmap_page_optimizable(page)) {\n+\t\t\tstruct mem_section *ms = __pfn_to_section(pfn);\n+\t\t\tunsigned long start = pfn;\n+\n+\t\t\tpfn = min(ALIGN(start, 1L << section_order(ms)), end_pfn);\n+\t\t\tpageblock_migratetype_init_range(start, pfn - start, migratetype,\n+\t\t\t\t\t\t\t isolate_pageblock);\n+\t\t\tcontinue;\n+\t\t}\n+\n \t\t__init_single_page(page, pfn, zone, nid);\n \t\tif (context == MEMINIT_HOTPLUG) {\n #ifdef CONFIG_ZONE_DEVICE\n@@ -1138,7 +1149,7 @@ void __ref memmap_init_zone_device(struct zone *zone,\n \t * Please note that MEMINIT_HOTPLUG path doesn't clear memmap\n \t * because this is done early in section_activate()\n \t */\n-\tpageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);\n+\tpageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE, false);\n \n \tpr_debug(\"%s initialised %lu pages in %ums\\n\", __func__,\n \t\tnr_pages, jiffies_to_msecs(jiffies - start));\n@@ -1963,7 +1974,7 @@ static void __init deferred_free_pages(unsigned long pfn,\n \tif (!nr_pages)\n \t\treturn;\n \n-\tpageblock_migratetype_init_range(pfn, nr_pages, MIGRATE_MOVABLE);\n+\tpageblock_migratetype_init_range(pfn, nr_pages, MIGRATE_MOVABLE, false);\n \n \tpage = pfn_to_page(pfn);\n \n", "prefixes": [ "23/49" ] }