Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline

Michal Hocko
2020-09-03T07:07:38Z

On Tue 01-09-20 08:46:15, Pavel Tatashin wrote:
[...]
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e9d5ab5d3ca0..d6d54922bfce 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1575,6 +1575,15 @@ static int __ref __offline_pages(unsigned long start_pfn,
> /* check again */
> ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> NULL, check_pages_isolated_cb);
> + /*
> + * per-cpu pages are drained in start_isolate_page_range, but if
> + * there are still pages that are not free, make sure that we
> + * drain again, because when we isolated range we might
> + * have raced with another thread that was adding pages to
> + * pcp list.

I would also add
* Forward progress should be still guaranteed because
* pages on the pcp list can only belong to MOVABLE_ZONE
* because has_unmovable_pages explicitly checks for
* PageBuddy on freed pages on other zones.
> + */
> + if (ret)
> + drain_all_pages(zone);
> } while (ret);
>
> /* Ok, all of our target is isolated.
> --
> 2.25.1
>

--
Michal Hocko
SUSE Labs