[FRAME] Use 'ready' pages in XCMP suspend logic (#2393)

Changes:
- `QueueFootprint` gets a new field; `ready_pages` that contains the
non-overweight and not yet processed pages.
- `XCMP` queue pallet is change to use the `ready_pages` instead of
`pages` to calculate the channel suspension thresholds.

This should give the XCMP queue pallet a more correct view of when to
suspend channels.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

cumulus/pallets/xcmp-queue/src/lib.rs

@@ -600,7 +600,7 @@ impl<T: Config> Pallet<T> {
 		let QueueConfigData { drop_threshold, .. } = <QueueConfig<T>>::get();
 		let fp = T::XcmpQueue::footprint(sender);
 		// Assume that it will not fit into the current page:
-		let new_pages = fp.pages.saturating_add(1);
+		let new_pages = fp.ready_pages.saturating_add(1);
 		if new_pages > drop_threshold {
 			// This should not happen since the channel should have been suspended in
 			// [`on_queue_changed`].
@@ -663,12 +663,12 @@ impl<T: Config> OnQueueChanged<ParaId> for Pallet<T> {
 		let mut suspended_channels = <InboundXcmpSuspended<T>>::get();
 		let suspended = suspended_channels.contains(&para);
 
-		if suspended && fp.pages <= resume_threshold {
+		if suspended && fp.ready_pages <= resume_threshold {
 			Self::send_signal(para, ChannelSignal::Resume);
 
 			suspended_channels.remove(&para);
 			<InboundXcmpSuspended<T>>::put(suspended_channels);
-		} else if !suspended && fp.pages >= suspend_threshold {
+		} else if !suspended && fp.ready_pages >= suspend_threshold {
 			log::warn!("XCMP queue for sibling {:?} is full; suspending channel.", para);
 			Self::send_signal(para, ChannelSignal::Suspend);
 

cumulus/pallets/xcmp-queue/src/mock.rs

@@ -247,6 +247,7 @@ impl<T: OnQueueChanged<ParaId>> EnqueueMessage<ParaId> for EnqueueToLocalStorage
 			}
 		}
 		footprint.pages = footprint.storage.size as u32 / 16; // Number does not matter
+		footprint.ready_pages = footprint.pages;
 		footprint
 	}
 }