> > Maybe I am not clear enough.
> >
> > I mean if we inflate balloon before live migration, for a 8GB guest, it takes
> about 5 Seconds for the inflating operation to finish.
>
> And these 5 seconds are spent where?
>
The time is spent on allocating the pages and send the allocated pages pfns to QEMU
through virtio.
> > For the PV solution, there is no need to inflate balloon before live
> > migration, the only cost is to traversing the free_list to construct
> > the free pages bitmap, and it takes about 20ms for a 8GB idle guest( less if
> there is less free pages), passing the free pages info to host will take about
> extra 3ms.
> >
> >
> > Liang
>
> So now let's please stop talking about solutions at a high level and discuss the
> interface changes you make in detail.
> What makes it faster? Better host/guest interface? No need to go through
> buddy allocator within guest? Less interrupts? Something else?
>
I assume you are familiar with the current virtio-balloon and how it works.
The new interface is very simple, send a request to the virtio-balloon driver,
The virtio-driver will travers the '&zone->free_area[order].free_list[t])' to
construct a 'free_page_bitmap', and then the driver will send the content
of 'free_page_bitmap' back to QEMU. That all the new interface does and
there are no ' alloc_page' related affairs, so it's faster.
Some code snippet:
----------------------------------------------
+static void mark_free_pages_bitmap(struct zone *zone,
+ unsigned long *free_page_bitmap, unsigned long pfn_gap) {
+ unsigned long pfn, flags, i;
+ unsigned int order, t;
+ struct list_head *curr;
+
+ if (zone_is_empty(zone))
+ return;
+
+ spin_lock_irqsave(&zone->lock, flags);
+
+ for_each_migratetype_order(order, t) {
+ list_for_each(curr, &zone->free_area[order].free_list[t]) {
+
+ pfn = page_to_pfn(list_entry(curr, struct page, lru));
+ for (i = 0; i < (1UL << order); i++) {
+ if ((pfn + i) >= PFN_4G)
+ set_bit_le(pfn + i - pfn_gap,
+ free_page_bitmap);
+ else
+ set_bit_le(pfn + i, free_page_bitmap);
+ }
+ }
+ }
+
+ spin_unlock_irqrestore(&zone->lock, flags); }
----------------------------------------------------
Sorry for my poor English and expression, if you still can't understand,
you could glance at the patch, total about 400 lines.
>
> > > --
> > > MST
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