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SubjectRe: [PATCH] mm/spase: never partially remove memmap for early section
On Tue, Jun 23, 2020 at 02:44:02PM +0200, David Hildenbrand wrote:
>On 23.06.20 11:42, Wei Yang wrote:
>> For early sections, we assumes its memmap will never be partially
>> removed. But current behavior breaks this.
>>
>> Let's correct it.
>>
>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>> ---
>> mm/sparse.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index b2b9a3e34696..1a0069f492f5 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -825,10 +825,10 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>> ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
>> }
>>
>> - if (section_is_early && memmap)
>> - free_map_bootmem(memmap);
>> - else
>> + if (!section_is_early)
>> depopulate_section_memmap(pfn, nr_pages, altmap);
>> + else if (memmap)
>> + free_map_bootmem(memmap);
>>
>> if (empty)
>> ms->section_mem_map = (unsigned long)NULL;
>>
>
>Agreed, that's what pfn_valid() and section_activate() expect.
>
>"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." - this
>is the case when hot-adding sub-sections into partially populated early
>sections, and has to be the case when re-hot-adding after hot-removing.
>
>Acked-by: David Hildenbrand <david@redhat.com>
>
>
>I am also not convinced that the complicated sparse_decode_mem_map()
>handling in that function is required - ms->section_mem_map &
>SECTION_MAP_MASK is sufficient for this use case of removing the memmap
>of a full early section once empty.
>

You mean remove this line?

memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);

Then what to passed to free_map_bootmem() ?

>--
>Thanks,
>
>David / dhildenb

--
Wei Yang
Help you, Help me

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