Re: [PATCH v1 09/10] mm/memory_hotplug: teach offline_pages() to not try forever

[Michal Hocko]

[I didn't really go through other patch but this one caught my eyes just
 because of the similar request proposed yesterday]

On Wed 23-05-18 17:11:50, David Hildenbrand wrote:
[...]
> @@ -1686,6 +1686,10 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	pfn = scan_movable_pages(start_pfn, end_pfn);
>  	if (pfn) { /* We have movable pages */
>  		ret = do_migrate_range(pfn, end_pfn);
> +		if (ret && !retry_forever) {
> +			ret = -EBUSY;
> +			goto failed_removal;
> +		}
>  		goto repeat;
>  	}
>  

Btw. this will not work in practice. Even a single temporary pin on a page
will fail way too easily. If you really need to control this then make
it a retry counter with default -1UL.

We really do need a better error reporting from do_migrate_range and
distinguish transient from permanent failures. In general we shouldn't
even get here for pages which are not migrateable...
-- 
Michal Hocko
SUSE Labs