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mm/sparse-vmemmap: fix DAX vmemmap accounting with optimization

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When vmemmap optimization is enabled for DAX, the nr_memmap_pages counter
in /proc/vmstat is incorrect.  The current code always accounts for the
full, non-optimized vmemmap size, but vmemmap optimization reduces the
actual number of vmemmap pages by reusing tail pages.  This causes the
system to overcount vmemmap usage, leading to inaccurate page statistics
in /proc/vmstat.

Fix this by introducing section_nr_vmemmap_pages(), which returns the
exact vmemmap page count for a given pfn range based on whether
optimization is in effect.

Link: https://lore.kernel.org/20260428081855.1249045-5-songmuchun@bytedance.com
Fixes: 15995a3524 ("mm: report per-page metadata information")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Muchun Song 2026-04-28 16:18:53 +08:00 committed by Andrew Morton
parent 3bbc54dd1b
commit 721a73e30c
1 changed files with 30 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
mm/sparse-vmemmap.c
View File

@ -647,6 +647,31 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
}
}
static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
{
const unsigned int order = pgmap ? pgmap->vmemmap_shift : 0;
const unsigned long pages_per_compound = 1UL << order;
VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SUBSECTION));
VM_WARN_ON_ONCE(nr_pages > PAGES_PER_SECTION);
if (!vmemmap_can_optimize(altmap, pgmap))
return DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE);
if (order < PFN_SECTION_SHIFT) {
VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, pages_per_compound));
return VMEMMAP_RESERVE_NR * nr_pages / pages_per_compound;
}
VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION));
if (IS_ALIGNED(pfn, pages_per_compound))
return VMEMMAP_RESERVE_NR;
return 0;
}
static struct page * __meminit populate_section_memmap(unsigned long pfn,
unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
struct dev_pagemap *pgmap)
@ -654,7 +679,7 @@ static struct page * __meminit populate_section_memmap(unsigned long pfn,
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));
memmap_pages_add(section_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap));
return page;
}
@ -665,7 +690,7 @@ 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)));
memmap_pages_add(-section_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap));
vmemmap_free(start, end, altmap);
}
@ -673,9 +698,10 @@ static void free_map_bootmem(struct page *memmap)
{
unsigned long start = (unsigned long)memmap;
unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);
unsigned long pfn = page_to_pfn(memmap);
memmap_boot_pages_add(-1L * (DIV_ROUND_UP(PAGES_PER_SECTION * sizeof(struct page),
PAGE_SIZE)));
memmap_boot_pages_add(-section_nr_vmemmap_pages(pfn, PAGES_PER_SECTION,
NULL, NULL));
vmemmap_free(start, end, NULL);
}