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SubjectRe: [PATCH 7/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case
On Mon, Feb 10, 2020 at 03:54:06PM +0800, Baoquan He wrote:
>On 02/10/20 at 02:08pm, Wei Yang wrote:
>> On Mon, Feb 10, 2020 at 11:41:05AM +0800, Baoquan He wrote:
>> >On 02/10/20 at 07:52am, Wei Yang wrote:
>> >> >---
>> >> > mm/sparse.c | 4 +++-
>> >> > 1 file changed, 3 insertions(+), 1 deletion(-)
>> >> >
>> >> >diff --git a/mm/sparse.c b/mm/sparse.c
>> >> >index 623755e88255..345d065ef6ce 100644
>> >> >--- a/mm/sparse.c
>> >> >+++ b/mm/sparse.c
>> >> >@@ -854,13 +854,15 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>> >> > ms->usage = NULL;
>> >> > }
>> >> > memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
>> >> >- ms->section_mem_map = (unsigned long)NULL;
>> >> > }
>> >> >
>> >> > if (section_is_early && memmap)
>> >> > free_map_bootmem(memmap);
>> >> > else
>> >> > depopulate_section_memmap(pfn, nr_pages, altmap);
>> >>
>> >> The crash happens in depopulate_section_memmap() when trying to get memmap by
>> >> pfn_to_page(). Can we pass memmap directly?
>> >
>> >Yes, that's also a good idea. While it needs to add a parameter for
>> >depopulate_section_memmap(), the parameter is useless for VMEMMAP
>> >though, I personally prefer the current fix which is a little simpler.
>> >
>>
>> Not a new parameter, but replace pfn with memmap.
>>
>> Not sure why the parameter is useless for VMEMMAP? memmap will be assigned to
>> start and finally pass to vmemmap_free().
>
>In section_deactivate(), per the code comments from Dan, we can know
>that:
>
> /*
> * section which only contains bootmem will be handled by
> * free_map_bootmem(), including a complete section, or partial
> * section which only has memory starting from the begining.
> */
> if (section_is_early && memmap)
> free_map_bootmem(memmap);
> else
> /*
> * section which contains region mixing bootmem with hot added
> * sub-section region, only sub-section region, complete
> * section. And in the mxied case, if hot remove the hot added
> * sub-section aligned part, no memmap is got in the current
> * code. So we still need pfn to calculate it for vmemmap case.
> * To me, whenever we need, it looks better that we always use
> * pfn to get its own memmap.
> */
> depopulate_section_memmap(pfn, nr_pages, altmap);
>
>This is why I would like to keep the current logic as is,only one line
>of code adjusting can fix the issue. Please let me know if I miss
>anything.
>

You are right. I missed this point.

>
>>
>> >Anyway, both is fine to me, I can update if you think passing memmap is
>> >better.
>> >
>> >>
>> >> >+
>> >> >+ if(!rc)
>> >> >+ ms->section_mem_map = (unsigned long)NULL;
>> >> > }
>> >> >
>> >> > static struct page * __meminit section_activate(int nid, unsigned long pfn,
>> >> >--
>> >> >2.17.2
>> >>
>> >> --
>> >> Wei Yang
>> >> Help you, Help me
>> >>
>>
>> --
>> Wei Yang
>> Help you, Help me
>>

--
Wei Yang
Help you, Help me

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