Acked-by: Zi Yan <z...@nvidia.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
Hi David, sorry for jumping in late
Hi,
not late at all :)
@@ -1157,6 +1083,7 @@ static void virtio_mem_set_fake_offline(unsigned long pfn,
SetPageDirty(page);
else
__SetPageOffline(page);
+ __SetPageOfflineSkippable(page);
VM_WARN_ON_ONCE(!PageOffline(page));
I think I am having some issues understanding this, let me see if I get
it.
- virtio-mem defines PageOffline pages, which are logically-offlined
pages within an onlined memory-block
PageOffline is a more generic concept also e.g., used by memory
balloning. virtio-mem uses that concept, yes.
- PageOffline pages have a refcount of '0' once they are properly
initialized, meaning that refcount > 0 implies somebody is holding
a refcount and that should not really happen
PageOffline pages currently always have a refcount > 0 (except
temporarily in this special case we are removing here). In the future,
it won't have a refcount at all.
- logically-offline pages belonging to onlined memory-blocks are marked
PageDirty,
while logically-offlined pages we allocated via alloc_contig_range are marked
PageOffline (I am getting a bit lost between fake-online, fake-offline, my
fault)
No, the code is confusing.
All pages are PageOffline. Only the ones that have not been onlined are
*in addition* PageDirty.
The relevant bit is documented in page-flags.h:
"When a memory block gets onlined, all pages are initialized with a
refcount of 1 and PageOffline(). generic_online_page() will take care of
clearing PageOffline()."
- If we want to release logically-offline pages belonging to an onlined
memory-block,
we ClearDirty them and be done
PageOffline gets cleared in both cases: See the comment in
virtio_mem_clear_fake_offline()
"/* generic_online_page() will clear PageOffline(). */"
I'll note that I am planning on removing that PageDirty() handling
completely, and also letting handling PageOffline() clearing be always
performed by memory freeing core (the latter is easier to achieve).
- If we want to release logically-offlined pages belonging we allocated
via alloc_contig_range, we clear PageOffline and be done
Yes, in the future that clearing will be done by the core (so the plan).
> - PageOfflineSkipabble are unmovable PageOffline pages, which cannot
be migrated?
Yes, but they can simply be skipped -- consider them memory holes we
(the driver) can rediscover when re-onlining the memory. See below.
- So for a PageOffline to be able to be migrated away must be Movable or
marked PageOfflineSkipabble, making do_migrate_range ignore it
Yes.
- PageOfflineSkipabble will be marked PageOffline upon re-onlining? Will
still be marked as PageOfflineSkipabble?
When re-onlining, the core will set them all PageOffline, and virtio-mem
will intercept page onlining using the page_online_cb.
virtio-mem will then online the actually plugged parts (->
generic_online_page(), which clears PageOffline and exposes them to the
buddy) and set the unplugged/hole parts as PageOfflineSkipabble again.
That logic resides in virtio_mem_online_page_cb().
+
+ /*
+ * Only PageOffline() pages that are marked "skippable" cannot
+ * be migrated but can be skipped when offlining. See
It is probably me, and nevermind the comment but I somehow find
"PageOfflineSkipabble are not migrated but skipped when offlining" a bit
easier.
Definitely. Thanks!
--
Cheers,
David / dhildenb
