Messages in this thread | | | Subject | Re: [PATCH RFC 2/8] mm: introduce PG_offline | From | David Hildenbrand <> | Date | Tue, 17 Apr 2018 13:50:01 +0200 |
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On 13.04.2018 15:40, Michal Hocko wrote: > On Fri 13-04-18 15:16:26, David Hildenbrand wrote: >> online_pages()/offline_pages() theoretically allows us to work on >> sub-section sizes. This is especially relevant in the context of >> virtualization. It e.g. allows us to add/remove memory to Linux in a VM in >> 4MB chunks. > > Well, theoretically possible but this would require a lot of auditing > because the hotplug and per section assumption is quite a spread one. > >> While the whole section is marked as online/offline, we have to know >> the state of each page. E.g. to not read memory that is not online >> during kexec() or to properly mark a section as offline as soon as all >> contained pages are offline. > > But you cannot use a page flag for that, I am afraid. Page flags are > extremely scarce resource. I haven't looked at the rest of the series > but _if_ we have a bit spare which I am not really sure about then you > should prove there are no other ways around this.
BTW, looking at the possible layouts of page->flags, I don't think it will be a problem adding this flag. Especially if we compile this flag only if really needed.
We could glue this flag to CONFIG_MEMORY_HOTPLUG_SUBSECTION to something like that, that will be set when our new driver is compiled. So this would not affect anybody just wanting to use ordinary DIMM based hotplug (CONFIG_MEMORY_HOTPLUG).
But I am open for other suggestions. I don't think PG_reserved is the right thing to use. And storing for each section which parts are online/offline is also something I would like to avoid.
--
Thanks,
David / dhildenb
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