On 25.03.21 17:36, Michal Hocko wrote:
On Thu 25-03-21 17:20:23, David Hildenbrand wrote:
On 25.03.21 17:07, Michal Hocko wrote:
On Thu 25-03-21 16:35:58, Michal Hocko wrote:
[...]
So there is indeed a difference. One way around that would be to mark
vmemmap pages (e.g. PageReserved && magic value stored somewhere in the
struct page - resembling bootmem vmemmaps) or mark section fully backing
vmemmaps as online (ugly).
I am not yet ready to give up on this. Here is a quick stab at the
pfn_to_online_page approach. It is not great but it is not really
terrible either. I think we can do better and skip
We both seem to have a different taste, to phrase it in a nice way :) ; but
well, you seem to have set your mind (just like I seem to have set mine when
trying to find a nice and somewhat-clean way to handle this when discussing
it in the past).
I definitely do not want to fight for a certain solution just for the
sake of it. I really dislike how the lifetime of the reserved space and
its accounting are completely detached. But hey, I do understand that
a worse solution from the design perspective can be better due to
practical reasons or constrains.
I haven't seen the hibernation problem before and I do recognize it is
a nasty one. If all it takes is to make pfn_to_online_page work (and my
previous attempt is incorrect because it should consult block rather
than section pfn range) and there are no other downsides then I would
still prefer to go with my proposal. If there are still other things to
plug then, well, practicality is going to win.
So before I give up on the "proper" design card, are there more
subtleties to watch for? You have certainly given this much more thought
than I have.
"Just one more thing" :)
With the pfn_to_online_page() change, I think what remains is
1. The contiguous zone thingy, which we discussed is not a deal breaker,
although sub-optimal and most probably not to be optimized in the future.
2. There corner cases issue with /dev/mem use case with offline memory
blocks I mentioned. Existing setups (!memmap_on_memory) are not
affected, so I guess we're fine.
3. valid_zones_show() has to be taught to only look at the !vmemmap
part, otherwise we'll no longer indicate "movable" after onlining to the
movable zone. Should be fairly easy.
We'll have pfn_to_online_section() succeed without SECTION_IS_ONLINE. I
think I/we removed all such code that purely relied on that flag for
optimizations like
if (!online_section(s))
continue;
I can give it some more thought, it could fly. At least zone shrinking
and hibernation should continue working as expected, which is a relief.
--
Thanks,
David / dhildenb
