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

Pavel Tatashin
2020-09-03T14:49:06Z

Thanks Michal, I will add your comments.

Pasha

On Thu, Sep 3, 2020 at 3:07 AM Michal Hocko <mhocko@suse.com> wrote:
>
> 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