Re: [PATCH RFC 2/8] mm: introduce PG_offline
- Date: Fri, 13 Apr 2018 15:40:47 +0200
- From: Michal Hocko <mhocko@xxxxxxxxxx>
- Subject: Re: [PATCH RFC 2/8] mm: introduce PG_offline
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.
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>