Messages in this thread | | | Date | Wed, 23 Jul 2008 11:48:00 +0900 | From | Yasunori Goto <> | Subject | Re: memory hotplug: hot-remove fails on lowest chunk in ZONE_MOVABLE |
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Hi.
> I've been testing memory hotplug on s390, on a system that starts w/o > memory in ZONE_MOVABLE at first, and then some memory chunks will be > added to ZONE_MOVABLE via memory hot-add. Now I observe the following > problem: > > Memory hot-remove of the lowest memory chunk in ZONE_MOVABLE will fail > because of some reserved pages at the beginning of each zone > (MIGRATE_RESERVED). > > During memory hot-add, setup_per_zone_pages_min() will be called from > online_pages() to redistribute/recalculate the reserved page blocks. > This will mark some page blocks at the beginning of each zone as > MIGRATE_RESERVE. Now, the memory chunk containing these blocks cannot > be set offline again, because only MIGRATE_MOVABLE pages can be isolated > (offline_pages -> start_isolate_page_range). > > So you cannot remove all the memory chunks that have been added via > memory hotplug. I'm not sure if I am missing something here, or if this > really is a bug. Any thoughts?
I believe you are right. Current hot-remove code is NOT perfect. You may remove some sections, but may not other sections, because there are some un-removable pages by some reasons (not only MIGRATE_RESERVED).
I think MIGRATE_RESERVED pages should be move to MIGRATE_MOVABLE when those pages must be removed, and should recalculate MIGRATE_RESERVED pages.
Bye.
-- Yasunori Goto
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