Re: [PATCH 3/6] KVM: Dirty memory tracking for performant checkpointing and improved live migration

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On Thu, May 5, 2016 at 6:57 AM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote:
2016-05-04 18:33+0000, Cao, Lei:
 On 5/4/2016 1:15 PM, Cao, Lei wrote:
 On 5/4/2016 9:13 AM, Radim Krčmář wrote:
 Good designs so far seem to be:
  memslot -> lockless radix tree
 and
  vcpu -> memslot -> list  (memslot -> vcpu -> list)


There is no need for lookup, the dirty log is fetched in sequence, so why use
 radix tree with added complexity but no benefit?

List can be designed to be lockless, so memslot -> lockless fixed list?

Never mind, lookup is needed to avoid duplicates. We can use list+bitmap, but
 it's obviously not as efficient as radix tree.

Are duplicates a significant problem?

(The dirtied page is marked as dirty, so we should have zero to very few duplicates, depending on how dirtying and vm-exit on write to clean page cooperate. Duplicates don't introduce any bugs and we could also check
 last few entries in the list to weed out most likely cases.)

I don't think duplicated pages are significant problem. The point is we don't lose pages.

I actually don't quite follow why there will be duplicated pages. Is it because lockless thing?

Thanks,
-Kai


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