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From: Muchun Song In-Reply-To: Date: Tue, 14 Apr 2026 10:28:24 +0800 Cc: Muchun Song , Andrew Morton , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260405125240.2558577-1-songmuchun@bytedance.com> <20260405125240.2558577-4-songmuchun@bytedance.com> To: "David Hildenbrand (Arm)" X-Migadu-Flow: FLOW_OUT > On Apr 14, 2026, at 02:39, David Hildenbrand (Arm) = wrote: >=20 > On 4/5/26 14:51, Muchun Song wrote: >> When HVO is enabled for DAX, the vmemmap page accounting is wrong = since >> it only accounts for non-HVO case. >>=20 >> Fix the accounting by introducing section_vmemmap_pages() that = returns >> the exact number of vmemmap pages needed for the given pfn range. >=20 > I guess only the accounting in /proc/meminfo is messed up, correct? No. It is in /proc/vmstat cat /proc/vmstat | grep memmap nr_memmap_pages 0 nr_memmap_boot_pages 2097163 >=20 >>=20 >> Fixes: 15995a352474 ("mm: report per-page metadata information") >=20 > Similarly, please send all fixes out separately. Will do in next version. >=20 >> Signed-off-by: Muchun Song >> --- >> mm/sparse-vmemmap.c | 30 ++++++++++++++++++++++++++---- >> 1 file changed, 26 insertions(+), 4 deletions(-) >>=20 >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c >> index 7aa9a97498eb..0ef96b1afbcc 100644 >> --- a/mm/sparse-vmemmap.c >> +++ b/mm/sparse-vmemmap.c >> @@ -724,6 +724,27 @@ static int fill_subsection_map(unsigned long = pfn, unsigned long nr_pages) >> return rc; >> } >>=20 >> +static int __meminit section_vmemmap_pages(unsigned long pfn, = unsigned long nr_pages, >> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap) >> +{ >> + unsigned int order =3D pgmap ? pgmap->vmemmap_shift : 0; >> + unsigned long pages_per_compound =3D 1L << order; >> + >> + VM_BUG_ON(!IS_ALIGNED(pfn | nr_pages, min(pages_per_compound, = PAGES_PER_SECTION))); >> + VM_BUG_ON(pfn_to_section_nr(pfn) !=3D pfn_to_section_nr(pfn + = nr_pages - 1)); >=20 > No new VM_BUG_ON. Ever. :) >=20 > VM_WARN_ON_ONCE() is your friend. Got it. >=20 >> + >> + if (!vmemmap_can_optimize(altmap, pgmap)) >> + return DIV_ROUND_UP(nr_pages * sizeof(struct page), = PAGE_SIZE); >> + >> + if (order < PFN_SECTION_SHIFT) >> + return VMEMMAP_RESERVE_NR * nr_pages / = pages_per_compound; >> + >> + if (IS_ALIGNED(pfn, pages_per_compound)) >> + return VMEMMAP_RESERVE_NR; >> + >> + return 0; >> +} >> + >> /* >> * To deactivate a memory region, there are 3 cases to handle: >> * >> @@ -775,11 +796,12 @@ static void section_deactivate(unsigned long = pfn, unsigned long nr_pages, >> * section_activate() and pfn_valid() . >> */ >> if (!section_is_early) { >> - memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * = sizeof(struct page), PAGE_SIZE))); >=20 > That's nice to be factored out in any case. >=20 > --=20 > Cheers, >=20 > David