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

[Andrew Morton]

On Wed, 26 Apr 2017 09:27:31 +0530 Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> 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?