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SubjectRe: [PATCH] mm/sparse: only sub-section aligned range would be populated
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On 30.06.20 04:14, Wei Yang wrote:
> There are two code path which invoke __populate_section_memmap()
>
> * sparse_init_nid()
> * sparse_add_section()
>
> For both case, we are sure the memory range is sub-section aligned.
>
> * we pass PAGES_PER_SECTION to sparse_init_nid()
> * we check range by check_pfn_span() before calling
> sparse_add_section()
>
> Also, the counterpart of __populate_section_memmap(), we don't do such
> calculation and check since the range is checked by check_pfn_span() in
> __remove_pages().
>
> Clear the calculation and check to keep it simple and comply with its
> counterpart.
>
> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> ---
> mm/sparse-vmemmap.c | 16 ++--------------
> 1 file changed, 2 insertions(+), 14 deletions(-)
>
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 0db7738d76e9..24b01ebae111 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -247,20 +247,8 @@ int __meminit vmemmap_populate_basepages(unsigned long start,
> struct page * __meminit __populate_section_memmap(unsigned long pfn,
> unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
> {
> - unsigned long start;
> - unsigned long end;
> -
> - /*
> - * The minimum granularity of memmap extensions is
> - * PAGES_PER_SUBSECTION as allocations are tracked in the
> - * 'subsection_map' bitmap of the section.
> - */
> - end = ALIGN(pfn + nr_pages, PAGES_PER_SUBSECTION);
> - pfn &= PAGE_SUBSECTION_MASK;
> - nr_pages = end - pfn;
> -
> - start = (unsigned long) pfn_to_page(pfn);
> - end = start + nr_pages * sizeof(struct page);
> + unsigned long start = (unsigned long) pfn_to_page(pfn);
> + unsigned long end = start + nr_pages * sizeof(struct page);
>
> if (vmemmap_populate(start, end, nid, altmap))
> return NULL;
>

Can we add a WARN_ON_ONCE to catch mis-use in the future?

if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) ||
!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION))
return NULL;

--
Thanks,

David / dhildenb

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