Re: [PATCH 14/14] mm/sparse: move memory hotplug bits to sparse-vmemmap.c

Lorenzo Stoakes (Oracle)
2026-03-17T20:09:06Z

On Tue, Mar 17, 2026 at 05:56:52PM +0100, David Hildenbrand (Arm) wrote:
> Let's move all memory hoptplug related code to sparse-vmemmap.c.
>
> We only have to expose sparse_index_init(). While at it, drop the
> definition of sparse_index_init() for !CONFIG_SPARSEMEM, which is unused,
> and place the declaration in internal.h.
>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

Looking through this it looks like it is just a code move modulo the other bits
you metion, overall very nice cleanup, so let me hotplug my:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Into this review!

OK I've actually cringed terribly at the puns here and maybe I'm cured for life
from doing that again ;)

Cheers, Lorenzo

> ---
> include/linux/mmzone.h | 1 -
> mm/internal.h | 4 +
> mm/sparse-vmemmap.c | 308 ++++++++++++++++++++++++++++++++++++++++
> mm/sparse.c | 314 +----------------------------------------
> 4 files changed, 314 insertions(+), 313 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index dcbbf36ed88c..e11513f581eb 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -2390,7 +2390,6 @@ static inline unsigned long next_present_section_nr(unsigned long section_nr)
> #endif
>
> #else
> -#define sparse_index_init(_sec, _nid) do {} while (0)
> #define sparse_vmemmap_init_nid_early(_nid) do {} while (0)
> #define sparse_vmemmap_init_nid_late(_nid) do {} while (0)
> #define pfn_in_present_section pfn_valid
> diff --git a/mm/internal.h b/mm/internal.h
> index 835a6f00134e..b1a9e9312ffe 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -965,6 +965,7 @@ void memmap_init_range(unsigned long, int, unsigned long, unsigned long,
> */
> #ifdef CONFIG_SPARSEMEM
> void sparse_init(void);
> +int sparse_index_init(unsigned long section_nr, int nid);
>
> static inline void sparse_init_one_section(struct mem_section *ms,
> unsigned long pnum, struct page *mem_map,
> @@ -1000,6 +1001,9 @@ static inline void __section_mark_present(struct mem_section *ms,
> static inline void sparse_init(void) {}
> #endif /* CONFIG_SPARSEMEM */
>
> +/*
> + * mm/sparse-vmemmap.c
> + */
> #ifdef CONFIG_SPARSEMEM_VMEMMAP
> void sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages);
> #else
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index f0690797667f..330579365a0f 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -591,3 +591,311 @@ void __init sparse_vmemmap_init_nid_late(int nid)
> hugetlb_vmemmap_init_late(nid);
> }
> #endif
> +
> +static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> + unsigned long nr_pages)
> +{
> + int idx = subsection_map_index(pfn);
> + int end = subsection_map_index(pfn + nr_pages - 1);
> +
> + bitmap_set(map, idx, end - idx + 1);
> +}
> +
> +void __init sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + int end_sec_nr = pfn_to_section_nr(pfn + nr_pages - 1);
> + unsigned long nr, start_sec_nr = pfn_to_section_nr(pfn);
> +
> + for (nr = start_sec_nr; nr <= end_sec_nr; nr++) {
> + struct mem_section *ms;
> + unsigned long pfns;
> +
> + pfns = min(nr_pages, PAGES_PER_SECTION
> + - (pfn & ~PAGE_SECTION_MASK));
> + ms = __nr_to_section(nr);
> + subsection_mask_set(ms->usage->subsection_map, pfn, pfns);
> +
> + pr_debug("%s: sec: %lu pfns: %lu set(%d, %d)\n", __func__, nr,
> + pfns, subsection_map_index(pfn),
> + subsection_map_index(pfn + pfns - 1));
> +
> + pfn += pfns;
> + nr_pages -= pfns;
> + }
> +}
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +
> +/* Mark all memory sections within the pfn range as online */
> +void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + unsigned long pfn;
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> + unsigned long section_nr = pfn_to_section_nr(pfn);
> + struct mem_section *ms = __nr_to_section(section_nr);
> +
> + ms->section_mem_map |= SECTION_IS_ONLINE;
> + }
> +}
> +
> +/* Mark all memory sections within the pfn range as offline */
> +void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + unsigned long pfn;
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> + unsigned long section_nr = pfn_to_section_nr(pfn);
> + struct mem_section *ms = __nr_to_section(section_nr);
> +
> + ms->section_mem_map &= ~SECTION_IS_ONLINE;
> + }
> +}
> +
> +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);
> +}
> +
> +static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap)
> +{
> + unsigned long start = (unsigned long) pfn_to_page(pfn);
> + unsigned long end = start + nr_pages * sizeof(struct page);
> +
> + 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);
> +
> + vmemmap_free(start, end, NULL);
> +}
> +
> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> + DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
> + struct mem_section *ms = __pfn_to_section(pfn);
> + unsigned long *subsection_map = ms->usage
> + ? &ms->usage->subsection_map[0] : NULL;
> +
> + subsection_mask_set(map, pfn, nr_pages);
> + if (subsection_map)
> + bitmap_and(tmp, map, subsection_map, SUBSECTIONS_PER_SECTION);
> +
> + if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
> + "section already deactivated (%#lx + %ld)\n",
> + pfn, nr_pages))
> + return -EINVAL;
> +
> + bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> + return 0;
> +}
> +
> +static bool is_subsection_map_empty(struct mem_section *ms)
> +{
> + return bitmap_empty(&ms->usage->subsection_map[0],
> + SUBSECTIONS_PER_SECTION);
> +}
> +
> +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + struct mem_section *ms = __pfn_to_section(pfn);
> + DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> + unsigned long *subsection_map;
> + int rc = 0;
> +
> + subsection_mask_set(map, pfn, nr_pages);
> +
> + subsection_map = &ms->usage->subsection_map[0];
> +
> + if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
> + rc = -EINVAL;
> + else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION))
> + rc = -EEXIST;
> + else
> + bitmap_or(subsection_map, map, subsection_map,
> + SUBSECTIONS_PER_SECTION);
> +
> + return rc;
> +}
> +
> +/*
> + * To deactivate a memory region, there are 3 cases to handle across
> + * two configurations (SPARSEMEM_VMEMMAP={y,n}):
> + *
> + * 1. deactivation of a partial hot-added section (only possible in
> + * the SPARSEMEM_VMEMMAP=y case).
> + * a) section was present at memory init.
> + * b) section was hot-added post memory init.
> + * 2. deactivation of a complete hot-added section.
> + * 3. deactivation of a complete section from memory init.
> + *
> + * For 1, when subsection_map does not empty we will not be freeing the
> + * usage map, but still need to free the vmemmap range.
> + *
> + * For 2 and 3, the SPARSEMEM_VMEMMAP={y,n} cases are unified
> + */
> +static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap)
> +{
> + struct mem_section *ms = __pfn_to_section(pfn);
> + bool section_is_early = early_section(ms);
> + struct page *memmap = NULL;
> + bool empty;
> +
> + if (clear_subsection_map(pfn, nr_pages))
> + return;
> +
> + empty = is_subsection_map_empty(ms);
> + if (empty) {
> + /*
> + * Mark the section invalid so that valid_section()
> + * return false. This prevents code from dereferencing
> + * ms->usage array.
> + */
> + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> +
> + /*
> + * When removing an early section, the usage map is kept (as the
> + * usage maps of other sections fall into the same page). It
> + * will be re-used when re-adding the section - which is then no
> + * longer an early section. If the usage map is PageReserved, it
> + * was allocated during boot.
> + */
> + if (!PageReserved(virt_to_page(ms->usage))) {
> + kfree_rcu(ms->usage, rcu);
> + WRITE_ONCE(ms->usage, NULL);
> + }
> + memmap = pfn_to_page(SECTION_ALIGN_DOWN(pfn));
> + }
> +
> + /*
> + * 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)));
> + 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)));
> + free_map_bootmem(memmap);
> + }
> +
> + if (empty)
> + ms->section_mem_map = (unsigned long)NULL;
> +}
> +
> +static struct page * __meminit section_activate(int nid, unsigned long pfn,
> + unsigned long nr_pages, struct vmem_altmap *altmap,
> + struct dev_pagemap *pgmap)
> +{
> + struct mem_section *ms = __pfn_to_section(pfn);
> + struct mem_section_usage *usage = NULL;
> + struct page *memmap;
> + int rc;
> +
> + if (!ms->usage) {
> + usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
> + if (!usage)
> + return ERR_PTR(-ENOMEM);
> + ms->usage = usage;
> + }
> +
> + rc = fill_subsection_map(pfn, nr_pages);
> + if (rc) {
> + if (usage)
> + ms->usage = NULL;
> + kfree(usage);
> + return ERR_PTR(rc);
> + }
> +
> + /*
> + * The early init code does not consider partially populated
> + * initial sections, it simply assumes that memory will never be
> + * referenced. If we hot-add memory into such a section then we
> + * do not need to populate the memmap and can simply reuse what
> + * is already there.
> + */
> + if (nr_pages < PAGES_PER_SECTION && early_section(ms))
> + return pfn_to_page(pfn);
> +
> + memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap);
> + if (!memmap) {
> + 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;
> +}
> +
> +/**
> + * sparse_add_section - add a memory section, or populate an existing one
> + * @nid: The node to add section on
> + * @start_pfn: start pfn of the memory range
> + * @nr_pages: number of pfns to add in the section
> + * @altmap: alternate pfns to allocate the memmap backing store
> + * @pgmap: alternate compound page geometry for devmap mappings
> + *
> + * This is only intended for hotplug.
> + *
> + * Note that only VMEMMAP supports sub-section aligned hotplug,
> + * the proper alignment and size are gated by check_pfn_span().
> + *
> + *
> + * Return:
> + * * 0 - On success.
> + * * -EEXIST - Section has been present.
> + * * -ENOMEM - Out of memory.
> + */
> +int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> + unsigned long nr_pages, struct vmem_altmap *altmap,
> + struct dev_pagemap *pgmap)
> +{
> + unsigned long section_nr = pfn_to_section_nr(start_pfn);
> + struct mem_section *ms;
> + struct page *memmap;
> + int ret;
> +
> + ret = sparse_index_init(section_nr, nid);
> + if (ret < 0)
> + return ret;
> +
> + memmap = section_activate(nid, start_pfn, nr_pages, altmap, pgmap);
> + if (IS_ERR(memmap))
> + return PTR_ERR(memmap);
> +
> + /*
> + * Poison uninitialized struct pages in order to catch invalid flags
> + * combinations.
> + */
> + page_init_poison(memmap, sizeof(struct page) * nr_pages);
> +
> + ms = __nr_to_section(section_nr);
> + __section_mark_present(ms, section_nr);
> +
> + /* Align memmap to section boundary in the subsection case */
> + if (section_nr_to_pfn(section_nr) != start_pfn)
> + memmap = pfn_to_page(section_nr_to_pfn(section_nr));
> + sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
> +
> + return 0;
> +}
> +
> +void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap)
> +{
> + struct mem_section *ms = __pfn_to_section(pfn);
> +
> + if (WARN_ON_ONCE(!valid_section(ms)))
> + return;
> +
> + section_deactivate(pfn, nr_pages, altmap);
> +}
> +#endif /* CONFIG_MEMORY_HOTPLUG */
> diff --git a/mm/sparse.c b/mm/sparse.c
> index bf620f3fe05d..007fd52c621e 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -79,7 +79,7 @@ static noinline struct mem_section __ref *sparse_index_alloc(int nid)
> return section;
> }
>
> -static int __meminit sparse_index_init(unsigned long section_nr, int nid)
> +int __meminit sparse_index_init(unsigned long section_nr, int nid)
> {
> unsigned long root = SECTION_NR_TO_ROOT(section_nr);
> struct mem_section *section;
> @@ -103,7 +103,7 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
> return 0;
> }
> #else /* !SPARSEMEM_EXTREME */
> -static inline int sparse_index_init(unsigned long section_nr, int nid)
> +int sparse_index_init(unsigned long section_nr, int nid)
> {
> return 0;
> }
> @@ -167,40 +167,6 @@ static inline unsigned long first_present_section_nr(void)
> return next_present_section_nr(-1);
> }
>
> -#ifdef CONFIG_SPARSEMEM_VMEMMAP
> -static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> - unsigned long nr_pages)
> -{
> - int idx = subsection_map_index(pfn);
> - int end = subsection_map_index(pfn + nr_pages - 1);
> -
> - bitmap_set(map, idx, end - idx + 1);
> -}
> -
> -void __init sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages)
> -{
> - int end_sec_nr = pfn_to_section_nr(pfn + nr_pages - 1);
> - unsigned long nr, start_sec_nr = pfn_to_section_nr(pfn);
> -
> - for (nr = start_sec_nr; nr <= end_sec_nr; nr++) {
> - struct mem_section *ms;
> - unsigned long pfns;
> -
> - pfns = min(nr_pages, PAGES_PER_SECTION
> - - (pfn & ~PAGE_SECTION_MASK));
> - ms = __nr_to_section(nr);
> - subsection_mask_set(ms->usage->subsection_map, pfn, pfns);
> -
> - pr_debug("%s: sec: %lu pfns: %lu set(%d, %d)\n", __func__, nr,
> - pfns, subsection_map_index(pfn),
> - subsection_map_index(pfn + pfns - 1));
> -
> - pfn += pfns;
> - nr_pages -= pfns;
> - }
> -}
> -#endif
> -
> /* Record a memory area against a node. */
> static void __init memory_present(int nid, unsigned long start, unsigned long end)
> {
> @@ -482,279 +448,3 @@ void __init sparse_init(void)
> sparse_init_nid(nid_begin, pnum_begin, pnum_end, map_count);
> vmemmap_populate_print_last();
> }
> -
> -#ifdef CONFIG_MEMORY_HOTPLUG
> -
> -/* Mark all memory sections within the pfn range as online */
> -void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> -{
> - unsigned long pfn;
> -
> - for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> - unsigned long section_nr = pfn_to_section_nr(pfn);
> - struct mem_section *ms = __nr_to_section(section_nr);
> -
> - ms->section_mem_map |= SECTION_IS_ONLINE;
> - }
> -}
> -
> -/* Mark all memory sections within the pfn range as offline */
> -void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> -{
> - unsigned long pfn;
> -
> - for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> - unsigned long section_nr = pfn_to_section_nr(pfn);
> - struct mem_section *ms = __nr_to_section(section_nr);
> -
> - ms->section_mem_map &= ~SECTION_IS_ONLINE;
> - }
> -}
> -
> -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);
> -}
> -
> -static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> -{
> - unsigned long start = (unsigned long) pfn_to_page(pfn);
> - unsigned long end = start + nr_pages * sizeof(struct page);
> -
> - 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);
> -
> - vmemmap_free(start, end, NULL);
> -}
> -
> -static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> -{
> - DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> - DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
> - struct mem_section *ms = __pfn_to_section(pfn);
> - unsigned long *subsection_map = ms->usage
> - ? &ms->usage->subsection_map[0] : NULL;
> -
> - subsection_mask_set(map, pfn, nr_pages);
> - if (subsection_map)
> - bitmap_and(tmp, map, subsection_map, SUBSECTIONS_PER_SECTION);
> -
> - if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
> - "section already deactivated (%#lx + %ld)\n",
> - pfn, nr_pages))
> - return -EINVAL;
> -
> - bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> - return 0;
> -}
> -
> -static bool is_subsection_map_empty(struct mem_section *ms)
> -{
> - return bitmap_empty(&ms->usage->subsection_map[0],
> - SUBSECTIONS_PER_SECTION);
> -}
> -
> -static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> -{
> - struct mem_section *ms = __pfn_to_section(pfn);
> - DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> - unsigned long *subsection_map;
> - int rc = 0;
> -
> - subsection_mask_set(map, pfn, nr_pages);
> -
> - subsection_map = &ms->usage->subsection_map[0];
> -
> - if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
> - rc = -EINVAL;
> - else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION))
> - rc = -EEXIST;
> - else
> - bitmap_or(subsection_map, map, subsection_map,
> - SUBSECTIONS_PER_SECTION);
> -
> - return rc;
> -}
> -
> -/*
> - * To deactivate a memory region, there are 3 cases to handle across
> - * two configurations (SPARSEMEM_VMEMMAP={y,n}):
> - *
> - * 1. deactivation of a partial hot-added section (only possible in
> - * the SPARSEMEM_VMEMMAP=y case).
> - * a) section was present at memory init.
> - * b) section was hot-added post memory init.
> - * 2. deactivation of a complete hot-added section.
> - * 3. deactivation of a complete section from memory init.
> - *
> - * For 1, when subsection_map does not empty we will not be freeing the
> - * usage map, but still need to free the vmemmap range.
> - *
> - * For 2 and 3, the SPARSEMEM_VMEMMAP={y,n} cases are unified
> - */
> -static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> -{
> - struct mem_section *ms = __pfn_to_section(pfn);
> - bool section_is_early = early_section(ms);
> - struct page *memmap = NULL;
> - bool empty;
> -
> - if (clear_subsection_map(pfn, nr_pages))
> - return;
> -
> - empty = is_subsection_map_empty(ms);
> - if (empty) {
> - /*
> - * Mark the section invalid so that valid_section()
> - * return false. This prevents code from dereferencing
> - * ms->usage array.
> - */
> - ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> -
> - /*
> - * When removing an early section, the usage map is kept (as the
> - * usage maps of other sections fall into the same page). It
> - * will be re-used when re-adding the section - which is then no
> - * longer an early section. If the usage map is PageReserved, it
> - * was allocated during boot.
> - */
> - if (!PageReserved(virt_to_page(ms->usage))) {
> - kfree_rcu(ms->usage, rcu);
> - WRITE_ONCE(ms->usage, NULL);
> - }
> - memmap = pfn_to_page(SECTION_ALIGN_DOWN(pfn));
> - }
> -
> - /*
> - * 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)));
> - 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)));
> - free_map_bootmem(memmap);
> - }
> -
> - if (empty)
> - ms->section_mem_map = (unsigned long)NULL;
> -}
> -
> -static struct page * __meminit section_activate(int nid, unsigned long pfn,
> - unsigned long nr_pages, struct vmem_altmap *altmap,
> - struct dev_pagemap *pgmap)
> -{
> - struct mem_section *ms = __pfn_to_section(pfn);
> - struct mem_section_usage *usage = NULL;
> - struct page *memmap;
> - int rc;
> -
> - if (!ms->usage) {
> - usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
> - if (!usage)
> - return ERR_PTR(-ENOMEM);
> - ms->usage = usage;
> - }
> -
> - rc = fill_subsection_map(pfn, nr_pages);
> - if (rc) {
> - if (usage)
> - ms->usage = NULL;
> - kfree(usage);
> - return ERR_PTR(rc);
> - }
> -
> - /*
> - * The early init code does not consider partially populated
> - * initial sections, it simply assumes that memory will never be
> - * referenced. If we hot-add memory into such a section then we
> - * do not need to populate the memmap and can simply reuse what
> - * is already there.
> - */
> - if (nr_pages < PAGES_PER_SECTION && early_section(ms))
> - return pfn_to_page(pfn);
> -
> - memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap);
> - if (!memmap) {
> - 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;
> -}
> -
> -/**
> - * sparse_add_section - add a memory section, or populate an existing one
> - * @nid: The node to add section on
> - * @start_pfn: start pfn of the memory range
> - * @nr_pages: number of pfns to add in the section
> - * @altmap: alternate pfns to allocate the memmap backing store
> - * @pgmap: alternate compound page geometry for devmap mappings
> - *
> - * This is only intended for hotplug.
> - *
> - * Note that only VMEMMAP supports sub-section aligned hotplug,
> - * the proper alignment and size are gated by check_pfn_span().
> - *
> - *
> - * Return:
> - * * 0 - On success.
> - * * -EEXIST - Section has been present.
> - * * -ENOMEM - Out of memory.
> - */
> -int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> - unsigned long nr_pages, struct vmem_altmap *altmap,
> - struct dev_pagemap *pgmap)
> -{
> - unsigned long section_nr = pfn_to_section_nr(start_pfn);
> - struct mem_section *ms;
> - struct page *memmap;
> - int ret;
> -
> - ret = sparse_index_init(section_nr, nid);
> - if (ret < 0)
> - return ret;
> -
> - memmap = section_activate(nid, start_pfn, nr_pages, altmap, pgmap);
> - if (IS_ERR(memmap))
> - return PTR_ERR(memmap);
> -
> - /*
> - * Poison uninitialized struct pages in order to catch invalid flags
> - * combinations.
> - */
> - page_init_poison(memmap, sizeof(struct page) * nr_pages);
> -
> - ms = __nr_to_section(section_nr);
> - __section_mark_present(ms, section_nr);
> -
> - /* Align memmap to section boundary in the subsection case */
> - if (section_nr_to_pfn(section_nr) != start_pfn)
> - memmap = pfn_to_page(section_nr_to_pfn(section_nr));
> - sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
> -
> - return 0;
> -}
> -
> -void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> -{
> - struct mem_section *ms = __pfn_to_section(pfn);
> -
> - if (WARN_ON_ONCE(!valid_section(ms)))
> - return;
> -
> - section_deactivate(pfn, nr_pages, altmap);
> -}
> -#endif /* CONFIG_MEMORY_HOTPLUG */
> --
> 2.43.0
>