Re: [PATCH V2] mm/madvise: Enable (soft|hard) offline of HugeTLB pages at PGD level

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

On 05/13/2017 03:05 AM, Andrew Morton wrote:
> On Wed, 26 Apr 2017 09:27:31 +0530 Anshuman Khandual <khandual@linux.vnet.ibm.com> wrote:
> 
>> Though migrating gigantic HugeTLB pages does not sound much like real
>> world use case, they can be affected by memory errors. Hence migration
>> at the PGD level HugeTLB pages should be supported just to enable soft
>> and hard offline use cases.
>>
>> While allocating the new gigantic HugeTLB page, it should not matter
>> whether new page comes from the same node or not. There would be very
>> few gigantic pages on the system afterall, we should not be bothered
>> about node locality when trying to save a big page from crashing.
>>
>> This introduces a new HugeTLB allocator called alloc_huge_page_nonid()
>> which will scan over all online nodes on the system and allocate a
>> single HugeTLB page.
>>
>> ...
>>
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1669,6 +1669,23 @@ struct page *__alloc_buddy_huge_page_with_mpol(struct hstate *h,
>>  	return __alloc_buddy_huge_page(h, vma, addr, NUMA_NO_NODE);
>>  }
>>  
>> +struct page *alloc_huge_page_nonid(struct hstate *h)
>> +{
>> +	struct page *page = NULL;
>> +	int nid = 0;
>> +
>> +	spin_lock(&hugetlb_lock);
>> +	if (h->free_huge_pages - h->resv_huge_pages > 0) {
>> +		for_each_online_node(nid) {
>> +			page = dequeue_huge_page_node(h, nid);
>> +			if (page)
>> +				break;
>> +		}
>> +	}
>> +	spin_unlock(&hugetlb_lock);
>> +	return page;
>> +}
>> +
>>  /*
>>   * This allocation function is useful in the context where vma is irrelevant.
>>   * E.g. soft-offlining uses this function because it only cares physical
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index fe64d7729a8e..d4f5710cf3f7 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1481,11 +1481,15 @@ EXPORT_SYMBOL(unpoison_memory);
>>  static struct page *new_page(struct page *p, unsigned long private, int **x)
>>  {
>>  	int nid = page_to_nid(p);
>> -	if (PageHuge(p))
>> +	if (PageHuge(p)) {
>> +		if (hstate_is_gigantic(page_hstate(compound_head(p))))
>> +			return alloc_huge_page_nonid(page_hstate(compound_head(p)));
>> +
>>  		return alloc_huge_page_node(page_hstate(compound_head(p)),
>>  						   nid);
>> -	else
>> +	} else {
>>  		return __alloc_pages_node(nid, GFP_HIGHUSER_MOVABLE, 0);
>> +	}
>>  }
> 
> Rather than adding alloc_huge_page_nonid(), would it be neater to teach
> alloc_huge_page_node() (actually dequeue_huge_page_node()) to understand
> nid==NUMA_NO_NODE?

Sure, will change dequeue_huge_page_node() to accommodate NUMA_NO_NODE and
let soft offline call with NUMA_NO_NODE in case of gigantic huge pages.

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