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SubjectRe: [PATCH] mm/sparse: only sub-section aligned range would be populated
On Tue, Jun 30, 2020 at 02:52:35PM +0200, David Hildenbrand wrote:
>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;

How about to add this into both population and depopulation?

>
>--
>Thanks,
>
>David / dhildenb

--
Wei Yang
Help you, Help me

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