From: Muchun Song <muchun.song@linux.dev>
To: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Rapoport <rppt@kernel.org>,
Vlastimil Babka <vbabka@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>, Michal Hocko <mhocko@suse.com>,
David Laight <david.laight.linux@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Oscar Salvador <osalvador@suse.de>,
David Hildenbrand <david@kernel.org>
Subject: Re: [PATCH v3 08/17] mm/sparse-vmemmap: support section-based vmemmap optimization
Date: Thu, 6 Aug 2026 11:04:35 +0800 [thread overview]
Message-ID: <978060e0-a202-43b2-b84d-b1950b2d28c1@linux.dev> (raw)
In-Reply-To: <20260804035535.2846016-9-songmuchun@bytedance.com>
On 2026/8/4 11:55, Muchun Song wrote:
> Teach sparse-vmemmap population code to use the compound page order
> when deciding whether a vmemmap page can be optimized.
>
> With this information, the common sparse-vmemmap population path can
> allocate or reuse shared tail vmemmap pages directly instead of relying
> on HugeTLB-specific handling.
>
> This centralizes vmemmap optimization logic in the sparse-vmemmap code,
> based on section metadata, and prepares for sharing the same mechanism
> across different users of vmemmap optimization, including HugeTLB and
> DAX.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> v2:
> - Keep vmemmap accounting and population logic in sparse-vmemmap.c
> (suggested by Mike Rapoport)
> - Move vmemmap_get_tail() before its first use instead of adding only a
> forward declaration in the previous patch (suggested by Mike Rapoport)
> - Simplify the PMD path handling for HVO-covered sections
> ---
> mm/sparse-vmemmap.c | 36 ++++++++++++++++++++++++++++++------
> mm/sparse.c | 4 ++--
> mm/sparse.h | 7 +++++++
> 3 files changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index b770fe2428fd..b69a7af76858 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -186,6 +186,11 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone *
>
> return tail;
> }
> +#else
> +static inline struct page *vmemmap_get_tail(unsigned int order, struct zone *zone)
> +{
> + return NULL;
> +}
> #endif
>
> static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
> @@ -193,12 +198,24 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in
> unsigned long ptpfn, unsigned long flags)
> {
> pte_t *pte = pte_offset_kernel(pmd, addr);
> + unsigned long pfn = page_to_pfn((struct page *)addr);
> +
> if (pte_none(ptep_get(pte))) {
> pte_t entry;
> - void *p;
> +
> + if (pfn_vmemmap_optimizable(pfn) && ptpfn == (unsigned long)-1) {
> + unsigned int order = pfn_to_section_order(pfn);
> + struct zone *zone = pfn_to_zone(pfn, node);
> + struct page *page = vmemmap_get_tail(order, zone);
> +
> + if (!page)
> + return NULL;
> + ptpfn = page_to_pfn(page);
> + }
>
> if (ptpfn == (unsigned long)-1) {
> - p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
> + void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
> +
> if (!p)
> return NULL;
> ptpfn = PHYS_PFN(__pa(p));
> @@ -217,7 +234,8 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in
> }
> entry = pfn_pte(ptpfn, PAGE_KERNEL);
> set_pte_at(&init_mm, addr, pte, entry);
> - }
> + } else if (WARN_ON_ONCE(pfn_vmemmap_optimizable(pfn)))
> + return NULL;
> return pte;
> }
>
> @@ -406,6 +424,9 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
> pmd_t *pmd;
>
> for (addr = start; addr < end; addr = next) {
> + unsigned long pfn = page_to_pfn((struct page *)addr);
> + const struct mem_section *ms = __pfn_to_section(pfn);
> +
> next = pmd_addr_end(addr, end);
>
> pgd = vmemmap_pgd_populate(addr, node);
> @@ -421,7 +442,7 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
> return -ENOMEM;
>
> pmd = pmd_offset(pud, addr);
> - if (pmd_none(pmdp_get(pmd))) {
> + if (pmd_none(pmdp_get(pmd)) && !section_vmemmap_optimizable(ms)) {
> void *p;
>
> p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
> @@ -439,8 +460,11 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
> */
> return -ENOMEM;
> }
> - } else if (vmemmap_check_pmd(pmd, node, addr, next))
> + } else if (vmemmap_check_pmd(pmd, node, addr, next)) {
> + if (WARN_ON_ONCE(section_vmemmap_optimizable(ms)))
> + return -ENOTSUPP;
> continue;
> + }
> if (vmemmap_populate_basepages(addr, next, node, altmap))
> return -ENOMEM;
> }
> @@ -648,7 +672,7 @@ 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,
> +int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
The kernel test robot reported a compilation issue: when
CONFIG_MEMORY_HOTPLUG = n && CONFIG_SPARSEMEM_VMEMMAP=y,
section_nr_vmemmap_pages is undefined. This problem is easy to fix, and
I will move the entire function outside the CONFIG_MEMORY_HOTPLUG guard
in the next version.
Thanks.
> struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
> {
> const struct mem_section *ms = __pfn_to_section(pfn);
> diff --git a/mm/sparse.c b/mm/sparse.c
> index ca9875f568d3..24555a32a5d9 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -315,8 +315,8 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
> nid, NULL, NULL);
> if (!map)
> panic("Failed to allocate memmap for section %lu\n", pnum);
> - memmap_boot_pages_add(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));
> sparse_init_early_section(nid, map, pnum, 0);
> }
> }
> diff --git a/mm/sparse.h b/mm/sparse.h
> index 6ad190ec48cf..f8f852f9f8a2 100644
> --- a/mm/sparse.h
> +++ b/mm/sparse.h
> @@ -105,8 +105,15 @@ static inline void sparse_init(void) {}
> */
> #ifdef CONFIG_SPARSEMEM_VMEMMAP
> void sparse_init_subsection_map(void);
> +int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap);
> #else
> static inline void sparse_init_subsection_map(void) {}
> +static inline int section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
> +{
> + return DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE);
> +}
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> #endif /* __MM_SPARSE_H */
next prev parent reply other threads:[~2026-08-06 3:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-04 3:55 [PATCH v3 00/17] mm: Introduce section-based vmemmap optimization for HugeTLB Muchun Song
2026-08-04 3:55 ` [PATCH v3 01/17] mm/sparse: relax struct mem_section size constraints Muchun Song
2026-08-04 3:55 ` [PATCH v3 02/17] mm/sparse-vmemmap: rename HVO order macros Muchun Song
2026-08-04 3:55 ` [PATCH v3 03/17] mm/mm_init: skip initializing shared vmemmap tail pages Muchun Song
2026-08-04 3:55 ` [PATCH v3 04/17] mm/sparse-vmemmap: initialize shared tail vmemmap pages on allocation Muchun Song
2026-08-04 3:55 ` [PATCH v3 05/17] mm/sparse-vmemmap: support section-based vmemmap accounting Muchun Song
2026-08-04 3:55 ` [PATCH v3 06/17] mm/mm_init: factor out pfn_to_zone() Muchun Song
2026-08-04 3:55 ` [PATCH v3 07/17] mm/sparse-vmemmap: move vmemmap_get_tail() before PTE population Muchun Song
2026-08-04 3:55 ` [PATCH v3 08/17] mm/sparse-vmemmap: support section-based vmemmap optimization Muchun Song
2026-08-06 3:04 ` Muchun Song [this message]
2026-08-04 3:55 ` [PATCH v3 09/17] mm/sparse: initialize memory sections earlier Muchun Song
2026-08-04 3:55 ` [PATCH v3 10/17] mm/hugetlb: switch HugeTLB to section-based vmemmap optimization Muchun Song
2026-08-04 3:55 ` [PATCH v3 11/17] mm/sparse-vmemmap: remove SPARSEMEM_VMEMMAP_PREINIT support Muchun Song
2026-08-04 3:55 ` [PATCH v3 12/17] mm/sparse: inline usemap allocation into sparse_init_nid() Muchun Song
2026-08-04 3:55 ` [PATCH v3 13/17] mm/sparse: remove section_map_size() Muchun Song
2026-08-04 3:55 ` [PATCH v3 14/17] mm/hugetlb: remove HUGE_BOOTMEM_HVO Muchun Song
2026-08-04 3:55 ` [PATCH v3 15/17] mm/hugetlb: remove HUGE_BOOTMEM_CMA Muchun Song
2026-08-04 3:55 ` [PATCH v3 16/17] mm/hugetlb: localize struct huge_bootmem_page Muchun Song
2026-08-04 3:55 ` [PATCH v3 17/17] mm/hugetlb: localize HUGE_BOOTMEM_ZONES_VALID Muchun Song
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