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    SubjectRe: [PATCH] mm/hotplug: fix offline undo_isolate_page_range()
    On Tue, Mar 12, 2019 at 09:42:16PM -0400, Qian Cai wrote:
    > +
    > + /*
    > + * Onlining will reset pagetype flags and makes migrate type
    > + * MOVABLE, so just need to decrease the number of isolated
    > + * pageblocks zone counter here.
    > + */
    > + for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
    > + int i;
    > +
    > + for (i = 0; i < pageblock_nr_pages; i++)
    > + if (pfn_valid_within(pfn + i)) {
    > + zone->nr_isolate_pageblock--;
    > + break;
    > + }
    > + }
    > +

    I do not really like this.

    I first thought about saving the value before entering start_isolate_page_range,
    but that could race with alloc_contig_range for instance.
    So, why not make start_isolate_page_range to return the actual number of isolated
    pageblocks?
    Sure, that would mean to change a bit how we threat its return code, but
    I think that it is pretty simple.
    In that way, we would only have to substract the value start_isolate_page_range
    gave us at the end of __offline__pages() to set nr_isolate_pageblock back to
    its original value.

    --
    Oscar Salvador
    SUSE L3

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