On Wed, Aug 22, 2012 at 12:33:17PM +0300, Michael S. Tsirkin wrote: > Hmm, so this will busy wait which is unelegant. > We need some event IMO. No, it does not busy wait. leak_balloon() is mutual exclusive with migration steps, so for the case we have one racing against the other, we really want leak_balloon() dropping the mutex temporarily to allow migration complete its work of refilling vb->pages list. Also, leak_balloon() calls tell_host(), which will potentially make it to schedule for each round of vb->pfns leak_balloon() will release. So, when remove_common() calls leak_balloon() looping on vb->num_pages, that won't become a tight loop. The scheme was apparently working before this series, and it will remain working after it. > Also, reading num_pages without a lock here > which seems wrong. I'll protect it with vb->balloon_lock mutex. That will be consistent with the lock protection scheme this patch is introducing for struct virtio_balloon elements. > A similar concern applies to normal leaking > of the balloon: here we might leak less than > required, then wait for the next config change > event. Just as before, same thing here. If you leaked less than required, balloon() will keep calling leak_balloon() until the balloon target is reached. This scheme was working before, and it will keep working after this patch. > How about we signal config_change > event when pages are back to pages_list? I really don't know what to tell you here, but, to me, it seems like an overcomplication that isn't directly entangled with this patch purposes. Besides, you cannot expect compation / migration happening and racing against leak_balloon() all the time to make them signal events to the later, so we might just be creating a wait-forever condition for leak_balloon(), IMHO. Cheers! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>