linux-kernel - Re: [PATCH v2 03/10] mm/memory_hotplug: simplify page offlining

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Message-ID: <20200904074653.GD15277@dhcp22.suse.cz>
Date:   Fri, 4 Sep 2020 09:46:53 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Baoquan He <bhe@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 03/10] mm/memory_hotplug: simplify page offlining

On Fri 04-09-20 07:47:45, David Hildenbrand wrote:
> 
> 
> > Am 03.09.2020 um 23:58 schrieb Andrew Morton <akpm@...ux-foundation.org>:
[...]
> > @@ -1589,16 +1567,27 @@ int __ref offline_pages(unsigned long st
> >            reason = "failure to dissolve huge pages";
> >            goto failed_removal_isolated;
> >        }
> > -        /* check again */
> > -        ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> > -                        NULL, check_pages_isolated_cb);
> > -    } while (ret);
> > -
> > -    /* Ok, all of our target is isolated.
> > -       We cannot do rollback at this point. */
> > -    walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> > -                  &offlined_pages, offline_isolated_pages_cb);
> > -    pr_info("Offlined Pages %ld\n", offlined_pages);
> > +
> > +        /*
> > +         * 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.
> > +         *
> > +         * 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 (test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE));
> 
> I think we have to do
> 
> ret = test_pages_isolated()
> if (ret)

Yes.
-- 
Michal Hocko
SUSE Labs