On Wed, Aug 22, 2012 at 11:19:04PM -0300, Rafael Aquini wrote: > 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. tell_host might not even cause an exit to host. Even if it does it does not involve guest scheduler. > 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. It seems that before we would always leak all requested memory in one go. I can't tell why we have a while loop there at all. Rusty, could you clarify please? > > > 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. > IIUC we never hit this path before. > > 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. So use wait_event or similar, check for existance of isolated pages. > 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>