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SubjectRe: [PATCH v3 3/5] mm,sparse: Add SECTION_USE_VMEMMAP flag
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On 25.07.19 18:02, Oscar Salvador wrote:
> When hot-removing memory, we need to be careful about two things:
>
> 1) Memory range must be memory_block aligned. This is what
> check_hotplug_memory_range() checks for.
>
> 2) If a range was hot-added using MHP_MEMMAP_ON_MEMORY, we need to check
> whether the caller is removing memory with the same granularity that
> it was added.

The second step does only apply to MMAP_ON_MEMORY and is not universally
true.

>
> So to check against case 2), we mark all sections used by vmemmap
> (not only the ones containing vmemmap pages, but all sections spanning
> the memory range) with SECTION_USE_VMEMMAP.

SECTION_USE_VMEMAP is misleding.

Rather SECTION_MMAP_ON_MEMORY (TBD). Please *really* add a description
(these sections)

>
> This will allow us to do some sanity checks when in hot-remove stage.
>

One idea: lookup the struct page of the lowest memory address you are
removing and test if it lies on a PageVmemmap(). Then, from the stored
info along the vmemmap page (start + length) you can test if all memory
the vmemmap is responsible for is removed.

This should work or am I missing something?

> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
> include/linux/memory_hotplug.h | 3 ++-
> include/linux/mmzone.h | 8 +++++++-
> mm/memory_hotplug.c | 2 +-
> mm/sparse.c | 9 +++++++--
> 4 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 45dece922d7c..6b20008d9297 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -366,7 +366,8 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap);
> extern bool is_memblock_offlined(struct memory_block *mem);
> extern int sparse_add_section(int nid, unsigned long pfn,
> - unsigned long nr_pages, struct vmem_altmap *altmap);
> + unsigned long nr_pages, struct vmem_altmap *altmap,
> + bool vmemmap_section);
> extern void sparse_remove_section(struct mem_section *ms,
> unsigned long pfn, unsigned long nr_pages,
> unsigned long map_offset, struct vmem_altmap *altmap);
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index d77d717c620c..259c326962f5 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1254,7 +1254,8 @@ extern size_t mem_section_usage_size(void);
> #define SECTION_HAS_MEM_MAP (1UL<<1)
> #define SECTION_IS_ONLINE (1UL<<2)
> #define SECTION_IS_EARLY (1UL<<3)
> -#define SECTION_MAP_LAST_BIT (1UL<<4)
> +#define SECTION_USE_VMEMMAP (1UL<<4)
> +#define SECTION_MAP_LAST_BIT (1UL<<5)
> #define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1))
> #define SECTION_NID_SHIFT 3
>
> @@ -1265,6 +1266,11 @@ static inline struct page *__section_mem_map_addr(struct mem_section *section)
> return (struct page *)map;
> }
>
> +static inline int vmemmap_section(struct mem_section *section)
> +{
> + return (section && (section->section_mem_map & SECTION_USE_VMEMMAP));
> +}
> +
> static inline int present_section(struct mem_section *section)
> {
> return (section && (section->section_mem_map & SECTION_MARKED_PRESENT));
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3d97c3711333..c2338703ce80 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -314,7 +314,7 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
>
> pfns = min(nr_pages, PAGES_PER_SECTION
> - (pfn & ~PAGE_SECTION_MASK));
> - err = sparse_add_section(nid, pfn, pfns, altmap);
> + err = sparse_add_section(nid, pfn, pfns, altmap, 0);
> if (err)
> break;
> pfn += pfns;
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 79355a86064f..09cac39e39d9 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -856,13 +856,18 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
> * * -ENOMEM - Out of memory.
> */
> int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> - unsigned long nr_pages, struct vmem_altmap *altmap)
> + unsigned long nr_pages, struct vmem_altmap *altmap,
> + bool vmemmap_section)
> {
> unsigned long section_nr = pfn_to_section_nr(start_pfn);
> + unsigned long flags = 0;
> struct mem_section *ms;
> struct page *memmap;
> int ret;
>
> + if (vmemmap_section)
> + flags = SECTION_USE_VMEMMAP;
> +
> ret = sparse_index_init(section_nr, nid);
> if (ret < 0)
> return ret;
> @@ -884,7 +889,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> /* Align memmap to section boundary in the subsection case */
> if (section_nr_to_pfn(section_nr) != start_pfn)
> memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr));
> - sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
> + sparse_init_one_section(ms, section_nr, memmap, ms->usage, flags);
>
> return 0;
> }
>


--

Thanks,

David / dhildenb

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