Re: [PATCH v5 4/5] mm: Make alloc_contig_range handle in-use hugetlb pages

[Michal Hocko]

On Wed 17-03-21 12:12:50, Oscar Salvador wrote:
> alloc_contig_range() will fail if it finds a HugeTLB page within the range,
> without a chance to handle them. Since HugeTLB pages can be migrated as any
> LRU or Movable page, it does not make sense to bail out without trying.
> Enable the interface to recognize in-use HugeTLB pages so we can migrate
> them, and have much better chances to succeed the call.
> 
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

I am still not entirely happy about this
> @@ -2347,7 +2351,19 @@ int isolate_or_dissolve_huge_page(struct page *page)
>  	if (hstate_is_gigantic(h))
>  		return -ENOMEM;
>  
> -	return alloc_and_dissolve_huge_page(h, head);
> +retry:
> +	if (page_count(head) && isolate_huge_page(head, list)) {
> +		ret = 0;
> +	} else if (!page_count(head)) {
> +		ret = alloc_and_dissolve_huge_page(h, head);
> +
> +		if (ret == -EBUSY && try_again) {
> +			try_again = false;
> +			goto retry;
> +		}
> +	}
> +
> +	return ret;
>  }

it would be imho better to retry inside alloc_and_dissolve_huge_page
because it already has its retry logic implemented.

But not something I will insist on.

-- 
Michal Hocko
SUSE Labs