On 24.10.19 10:42, Michal Hocko wrote:
On Wed 23-10-19 12:03:51, David Hildenbrand wrote:
Do you see any downsides?
The only downside I see is that we get more false negatives on
has_unmovable_pages(), eventually resulting in the offlining stage after
isolation to loop forever (as some PageOffline() pages are not movable
(especially, XEN balloon, HyperV balloon), there won't be progress).
I somewhat don't like forcing everybody that uses PageOffline() (especially
all users of balloon compaction) to implement memory notifiers just to avoid
that. Maybe, we even want to use PageOffline() in the future in the core
(e.g., for memory holes instead of PG_reserved or similar).
There is only a handful of those and we need to deal with them anyway.
If you do not want to enforce them to create their own notifiers then we
can accomodate the hotplug code. __test_page_isolated_in_pageblock resp.
Yeah, I would prefer offlining code to be able to deal with that without
notifier changes for all users.
the call chain up can distinguish temporary and permanent failures
(EAGAIN vs. EBUSY). The current state when we always return EBUSY and
keep retrying for ever is not optimal at all, right? A referenced PageOffline
Very right!
could be an example of EBUSY all other failures where we are effectively
waiting for pages to get freed finaly would be EAGAIN.
We have to watch out for PageOffline() pages that are actually movable
(balloon compaction). But that doesn't sound too hard.
It is a bit late in the process because a large portion of the work has
been done already but this doesn't sound like something to lose sleep
over.
Right. I'll look into that to find out if this would work. And see if I
can reproduce what I described at all (theoretical thoughts) :)
Again, thanks for looking into this Michal!
--
Thanks,
David / dhildenb
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