Messages in this thread | | | Date | Fri, 19 Jun 2015 10:52:47 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH 3/5] vhost: support upto 509 memory regions |
| |
On 19/06/2015 10:05, Michael S. Tsirkin wrote: > > No, only destruction of the memory region frees it. address_space_map > > takes a reference to the memory region and address_space_unmap releases it. > > > > Paolo > > Confused. So can we call mmap(MAP_NORESERVE) in address_space_unmap > after we detect refcount is 0?
No, because in the meanwhile another DIMM could have been hotplugged at the same place where the old one was. This is legal:
user guest QEMU ---------------------------------------------------------------------------------------- start I/O '---------------> address_space_map device_del '-------------------> receives SCI executes _EJ0 '---------------> memory_region_del_subregion object_unparent device_add '-----------------------------------------> device_set_realized hotplug_handler_plug pc_machine_device_plug_cb pc_dimm_plug memory_region_add_subregion
I/O finishes address_space_unmap
Surprise removal similarly could be done in QEMU, but it will hold to some resources for as long as the device backends need them.
Paolo
| |