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Don't sync dirty bitmaps in postcopy 

Once we're in postcopy the source processors are stopped and memory
shouldn't change any more, so there's no need to look at the dirty
map.

There are two notes to this:
  1) If we do resync and a page had changed then the page would get
     sent again, which the destination wouldn't allow (since it might
     have also modified the page)
  2) Before disabling this I'd seen very rare cases where a page had been
     marked dirtied although the memory contents are apparently identical

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2015-11-05 18:11:13 +00:00 committed by Juan Quintela
parent c53b7ddc61
commit 663e6c1df8
1 changed files with 5 additions and 2 deletions
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7
migration/ram.c
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@ -1846,7 +1846,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
{
rcu_read_lock();
migration_bitmap_sync();
if (!migration_in_postcopy(migrate_get_current())) {
migration_bitmap_sync();
}
ram_control_before_iterate(f, RAM_CONTROL_FINISH);
@ -1881,7 +1883,8 @@ static void ram_save_pending(QEMUFile *f, void *opaque, uint64_t max_size,
remaining_size = ram_save_remaining() * TARGET_PAGE_SIZE;
if (remaining_size < max_size) {
if (!migration_in_postcopy(migrate_get_current()) &&
remaining_size < max_size) {
qemu_mutex_lock_iothread();
rcu_read_lock();
migration_bitmap_sync();