On 01/04/2012 12:22 PM, Peter Lieven wrote:
There were patches to move RAM migration to a separate thread. The
problem is that they broke block migration.
However, asynchronous NBD is in and streaming will follow suit soon.
As soon as we have those two features, we might as well remove the
block migration code.
ok, so its a matter of time, right?
Well, there are other solutions of varying complexity in the works, that
might remove the need for the migration thread or at least reduce the
problem (post-copy migration, XBRLE, vectorized hot loops). But yes, we
are aware of the problem and we should solve it in one way or the other.
would it make sense to patch ram_save_block to always process a full ram
block?
If I understand the proposal, then migration would hardly be live
anymore. The biggest RAM block in a 32G machine is, well, 32G big.
Other RAM blocks are for the VRAM and for some BIOS data, but they are
very small in proportion.
- in stage 3 the vm is stopped, right? so there can't be any more dirty
blocks after scanning the whole memory once?
No, stage 3 is entered when there are very few dirty memory pages
remaining. This may happen after scanning the whole memory many times.
It may even never happen if migration does not converge because of low
bandwidth or too strict downtime requirements.
Paolo
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