On Tue, 17 Jul 2012 13:50:42 -0300 Rafael Aquini <aquini@xxxxxxxxxx> wrote: > Besides making balloon pages movable at allocation time and introducing > the necessary primitives to perform balloon page migration/compaction, > this patch also introduces the following locking scheme to provide the > proper synchronization and protection for struct virtio_balloon elements > against concurrent accesses due to parallel operations introduced by > memory compaction / page migration. > - balloon_lock (mutex) : synchronizes the access demand to elements of > struct virtio_balloon and its queue operations; > - pages_lock (spinlock): special protection to balloon pages list against > concurrent list handling operations; > > ... > > + balloon_mapping->a_ops = &virtio_balloon_aops; > + balloon_mapping->backing_dev_info = (void *)vb; hoo boy. We're making page->mapping->backing_dev_info point at a struct which does not have type `struct backing_dev_info'. And then we are exposing that page to core MM functions. So we're hoping that core MM will never walk down page->mapping->backing_dev_info and explode. That's nasty, hacky and fragile. -- 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>