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

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Date:   Thu, 3 Sep 2020 09:43:27 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during
 memory offline

Thanks Michal, I will add your comments.

Pasha

On Thu, Sep 3, 2020 at 3:07 AM Michal Hocko <mhocko@...e.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