Keir Fraser wrote:
On 15/09/2009 22:25, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:
No, it doesn't. I agree that after the first migration tot_pages will have
increased to 0x83ed. But I do not agree that it will continue to increase by
three pages on each future migration. Look at it this way -- three GPFNs
(guest-physical pages) have changed from xenheap pages to domheap pages
across that first migration. On future migrations they will be migrated just
like any other ordinary domheap page, since that's what they now are. And
tot_pages will therefore not change. Right?
Actually of course you do the right thing with the shinfo page, so actually
one page per migration does get switched back to being a Xenheap page (the
shinfo page) and tot_pages actually increases by 3 on the first migration,
then decreases by 1 when shinfo gets remapped by the PV drivers. Then
increases by 1 on every future migration (which is the shinfo Xenheap page
getting changed into a domheap page), and then decreases by 1 when shinfo
gets remapped by the PV drivers.
But even setting things out exactly right as above, the end result is the
same: I *still* cannot explain Annie's result.
The bug in her driver is that its only remapping shinfo page, and NOT
the 2 shared grant frames. tot_pages hence increases by 2 every
migration. I can see all in kdb. tot_pages goes up by 3, then down by 1
as shared info frame is remapped, and remains there. Next migration, it
goes up by 3, down by 1 again. So each migration leaks 2 frames. The initial
difference is 21 frames between tot and max, hence after 10 migrations
it fails. (BTW, no max_mem specified in config file, I'm told it means no POD).
On linux side, driver remaps shinfo page + both grant frames. So, it goes up
by 3 for a moment, then comes remap and down by 3, back to where it was. If
tot_pages == max_pages, then mig will fail. Which brings me to a question,
to test out balloon changes, what would be the best way to get tot_pages
equal to max_pages. xm mem-set doesn't quite get me there. Occassionally
I see the two same after starting guest, but I've not figured out what
causes that to happen.
thakns
Mukesh
-- Keir
This is why I still cannot understand or explain Annie's experimental
result.
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