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Hi MST,

I have measured the performance when using a 32K page bitmap,

Just to make sure. Do you mean a 32Kbyte bitmap?
Covering 1Gbyte of memory?

Yes.

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and inflate the balloon to 3GB
of an idle guest with 4GB RAM.

Should take 3 requests then, right?

No,  we can't assign the PFN when allocating page in balloon driver,
So the PFNs of pages allocated may be across a large range,  we will
tell the host once the pfn_max -pfn_min >= 0x40000(1GB range), so the
requests count is most likely to be more than 3.

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Now:
total inflating time: 338ms
the count of virtio data transmission:  373

Why was this so high? I would expect 3 transmissions.

I follow your suggestion:
----------------------------------------------------------------------
-------------- Suggestion to address all above comments:
	1. allocate a bunch of pages and link them up,
	   calculating the min and the max pfn.
	   if max-min exceeds the allocated bitmap size,
	   tell host.
	2. limit allocated bitmap size to something reasonable.
	   How about 32Kbytes? This is 256kilo bit in the map, which comes
	   out to 1Giga bytes of memory in the balloon.
----------------------------------------------------------------------
--------------- Because the PFNs of the allocated pages are not linear
increased, so 3 transmissions are  impossible.


Liang

Interesting. How about instead of tell host, we do multiple scans, each time
ignoring pages out of range?

	for (pfn = min pfn; pfn < max pfn; pfn += 1G) {
		foreach page
			if page pfn < pfn || page pfn >= pfn + 1G
				continue
			set bit
		tell host
	}

That means we have to allocate/free all the requested pages first, and then tell the host.
It works fine for inflating, but for deflating, because the page has been deleted from the vb-> vb_dev_info->pages,
so, we have to use a struct to save the dequeued pages before calling release_pages_balloon(),
 I think a page bitmap is the best struct to save these pages, because it consumes less memory.
And that bitmap should be large enough to save pfn 0 to max_pfn.

If the above is true, then we are back to the square one. we really need a large page bitmap. Right?

Liang