From: Muchun Song Date: Tue, 28 Apr 2026 08:18:50 +0000 (+0800) Subject: mm/sparse-vmemmap: fix vmemmap accounting underflow X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c373f7f98e6ad591c85d40548cf8b6443be69311;p=thirdparty%2Fkernel%2Flinux.git mm/sparse-vmemmap: fix vmemmap accounting underflow Patch series "mm: Fix vmemmap optimization accounting and initialization", v8. The series fixes several bugs in vmemmap optimization, mainly around incorrect page accounting and memmap initialization in DAX and memory hotplug paths. It also fixes pageblock migratetype initialization and struct page initialization for ZONE_DEVICE compound pages. Patches 1-4 fix vmemmap accounting issues. Patch 1 fixes an accounting underflow in the section activation failure path by moving vmemmap page accounting into the lower-level allocation and freeing helpers. Patch 2 fixes incorrect altmap passing in the memory hotplug error path. Patch 3 passes pgmap through memory deactivation paths so the teardown side can determine whether vmemmap optimization was in effect. Patch 4 uses that information to account the optimized DAX vmemmap size correctly. Patches 5-6 fix initialization issues in mm/mm_init. One makes sure all pageblocks in ZONE_DEVICE compound pages get their migratetype initialized. The other fixes a case where DAX memory hotplug reuses an unoptimized early-section memmap while compound_nr_pages() still assumes vmemmap optimization, leaving tail struct pages uninitialized. This patch (of 6): In section_activate(), if populate_section_memmap() fails, the error handling path calls section_deactivate() to roll back the state. This causes a vmemmap accounting imbalance. Since commit c3576889d87b ("mm: fix accounting of memmap pages"), memmap pages are accounted for only after populate_section_memmap() succeeds. However, the failure path unconditionally calls section_deactivate(), which decreases the vmemmap count. Consequently, a failure in populate_section_memmap() leads to an accounting underflow, incorrectly reducing the system's tracked vmemmap usage. Fix this more thoroughly by moving all accounting calls into the lower level functions that actually perform the vmemmap allocation and freeing: - populate_section_memmap() accounts for newly allocated vmemmap pages - depopulate_section_memmap() unaccounts when vmemmap is freed This ensures proper accounting in all code paths, including error handling and early section cases. Link: https://lore.kernel.org/20260428081855.1249045-1-songmuchun@bytedance.com Link: https://lore.kernel.org/20260428081855.1249045-2-songmuchun@bytedance.com Fixes: c3576889d87b ("mm: fix accounting of memmap pages") Signed-off-by: Muchun Song Acked-by: Mike Rapoport (Microsoft) Acked-by: Oscar Salvador Acked-by: David Hildenbrand (Arm) Acked-by: Liam R. Howlett Cc: "Aneesh Kumar K.V" Cc: Joao Martins Cc: Lorenzo Stoakes Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Nicholas Piggin Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c index 43f82621dd92..60e55e78d7ff 100644 --- a/mm/sparse-vmemmap.c +++ b/mm/sparse-vmemmap.c @@ -651,7 +651,12 @@ static struct page * __meminit populate_section_memmap(unsigned long pfn, unsigned long nr_pages, int nid, struct vmem_altmap *altmap, struct dev_pagemap *pgmap) { - return __populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap); + struct page *page = __populate_section_memmap(pfn, nr_pages, nid, altmap, + pgmap); + + memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); + + return page; } static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages, @@ -660,13 +665,17 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages, unsigned long start = (unsigned long) pfn_to_page(pfn); unsigned long end = start + nr_pages * sizeof(struct page); + memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE))); vmemmap_free(start, end, altmap); } + static void free_map_bootmem(struct page *memmap) { unsigned long start = (unsigned long)memmap; unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION); + memmap_boot_pages_add(-1L * (DIV_ROUND_UP(PAGES_PER_SECTION * sizeof(struct page), + PAGE_SIZE))); vmemmap_free(start, end, NULL); } @@ -769,14 +778,10 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, * The memmap of early sections is always fully populated. See * section_activate() and pfn_valid() . */ - if (!section_is_early) { - memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE))); + if (!section_is_early) depopulate_section_memmap(pfn, nr_pages, altmap); - } else if (memmap) { - memmap_boot_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), - PAGE_SIZE))); + else if (memmap) free_map_bootmem(memmap); - } if (empty) ms->section_mem_map = (unsigned long)NULL; @@ -821,7 +826,6 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn, section_deactivate(pfn, nr_pages, altmap); return ERR_PTR(-ENOMEM); } - memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); return memmap; }