Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

Aneesh Kumar K.V
2019-06-14T16:18:34Z

On 6/14/19 9:05 PM, Oscar Salvador wrote:
> On Fri, Jun 14, 2019 at 02:28:40PM +0530, Aneesh Kumar K.V wrote:
>> Can you check with this change on ppc64. I haven't reviewed this series yet.
>> I did limited testing with change . Before merging this I need to go
>> through the full series again. The vmemmap poplulate on ppc64 needs to
>> handle two translation mode (hash and radix). With respect to vmemap
>> hash doesn't setup a translation in the linux page table. Hence we need
>> to make sure we don't try to setup a mapping for a range which is
>> arleady convered by an existing mapping.
>>
>> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
>> index a4e17a979e45..15c342f0a543 100644
>> --- a/arch/powerpc/mm/init_64.c
>> +++ b/arch/powerpc/mm/init_64.c
>> @@ -88,16 +88,23 @@ static unsigned long __meminit vmemmap_section_start(unsigned long page)
>> * which overlaps this vmemmap page is initialised then this page is
>> * initialised already.
>> */
>> -static int __meminit vmemmap_populated(unsigned long start, int page_size)
>> +static bool __meminit vmemmap_populated(unsigned long start, int page_size)
>> {
>> unsigned long end = start + page_size;
>> start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
>>
>> - for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
>> - if (pfn_valid(page_to_pfn((struct page *)start)))
>> - return 1;
>> + for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page))) {
>>
>> - return 0;
>> + struct mem_section *ms;
>> + unsigned long pfn = page_to_pfn((struct page *)start);
>> +
>> + if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>> + return 0;
>
> I might be missing something, but is this right?
> Having a section_nr above NR_MEM_SECTIONS is invalid, but if we return 0 here,
> vmemmap_populate will go on and populate it.

I should drop that completely. We should not hit that condition at all.
I will send a final patch once I go through the full patch series making
sure we are not breaking any ppc64 details.

Wondering why we did the below

#if defined(ARCH_SUBSECTION_SHIFT)
#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
#elif defined(PMD_SHIFT)
#define SUBSECTION_SHIFT (PMD_SHIFT)
#else
/*
* Memory hotplug enabled platforms avoid this default because they
* either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant, but
* this is kept as a backstop to allow compilation on
* !ARCH_ENABLE_MEMORY_HOTPLUG archs.
*/
#define SUBSECTION_SHIFT 21
#endif

why not

#if defined(ARCH_SUBSECTION_SHIFT)
#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
#else
#define SUBSECTION_SHIFT SECTION_SHIFT
#endif

ie, if SUBSECTION is not supported by arch we have one sub-section per
section?

-aneesh