Hi all! I have some confusion about the dirty bitmap during migration. I have digged into the code. I figure out that every now and then during migration, the dirty bitmap will be grabbed from the kernel space through ioctl(KVM_GET_DIRTY_LOG), and then be used to update qemu's dirty bitmap. However I think this mechanism leads to resendness of some NON-dirty pages.
Take the first iteration of precopy for instance, during which all the pages will be sent. Before that during the migration setup, the ioctl(KVM_GET_DIRTY_LOG) is called once, so the kernel begins to produce the dirty bitmap from this moment. When the pages "that haven't been sent" are written, the kernel space marks them as dirty. However I don't think this is correct, because these pages will be sent during this and the next iterations with the same content (if they are not written again after they are sent). It only makes sense to mark the pages which have already been sent during one iteration as dirty when they are written. Am I right about this consideration? If I am right, is there some advice to improve this? Thanks, Chunguang Li
