On 09/13/2010 03:32 AM, Kevin Wolf wrote:
Am 11.09.2010 16:04, schrieb Anthony Liguori:
This fixes a couple nasty problems relating to live migration.
1) When dealing with shared storage with weak coherence (i.e. NFS), even if
we re-read, we may end up with undesired caching. By delaying any reads
until we absolutely have to, we decrease the likelihood of any undesirable
caching.
2) When dealing with copy-on-read, the local storage acts as a cache. We need
to make sure to avoid any reads to avoid polluting the local cache.
Signed-off-by: Anthony Liguori<aligu...@us.ibm.com>
I think we should also delay even opening the image file at all to the
latest possible point to avoid that new problems of this kind are
introduced. Ideally, opening the image would be the very last thing we
do before telling the migration source that we're set and it should
close the images.
There's a lot of possible failure scenarios that opening an image file
can introduce. Fortunately, I don't think we have a strict requirement
for it provided that we make a couple of reasonable changes.
Even better would be to only open the image when the source has already
closed it (we could completely avoid the invalidation/reopen then), but
I think you were afraid that we might lose the image on both ends.
Yeah, one of the key design points of live migration is to minimize the
number of failure scenarios where you lose a VM. If someone typed the
wrong command line or shared storage hasn't been mounted yet and we
delay failure until live migration is in the critical path, that would
be terribly unfortunate.
Regards,
Anthony Liguori
Kevin
