Inhibit ballooning during postcopy
commit371ff5a3f04cd7d05bab49ac6e80da319026d95b
authorDr. David Alan Gilbert <dgilbert@redhat.com>
Thu, 5 Nov 2015 18:11:23 +0000 (5 18:11 +0000)
committerJuan Quintela <quintela@redhat.com>
Tue, 10 Nov 2015 14:00:28 +0000 (10 15:00 +0100)
tree189c53ba78d63014f4976575de6fa55c0f7b2da0
parent58b7c17e226aa4d3b943ea22c1d1309126de146b
Inhibit ballooning during postcopy

Postcopy detects accesses to pages that haven't been transferred yet
using userfaultfd, and it causes exceptions on pages that are 'not
present'.
Ballooning also causes pages to be marked as 'not present' when the
guest inflates the balloon.
Potentially a balloon could be inflated to discard pages that are
currently inflight during postcopy and that may be arriving at about
the same time.

To avoid this confusion, disable ballooning during postcopy.

When disabled we drop balloon requests from the guest.  Since ballooning
is generally initiated by the host, the management system should avoid
initiating any balloon instructions to the guest during migration,
although it's not possible to know how long it would take a guest to
process a request made prior to the start of migration.
Guest initiated ballooning will not know if it's really freed a page
of host memory or not.

Queueing the requests until after migration would be nice, but is
non-trivial, since the set of inflate/deflate requests have to
be compared with the state of the page to know what the final
outcome is allowed to be.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
balloon.c
hw/virtio/virtio-balloon.c
include/sysemu/balloon.h
migration/postcopy-ram.c