On Thu, Mar 28, 2013 at 5:29 PM, Vasilis Liaskovitis <vasilis.liaskovi...@profitbricks.com> wrote: > Hi, > > [...] >>> > > >>> > > I haven't updated the series for a while, but I can rework if there is >>> > > a more >>> > > clear direction for the community. >>> > > >>> > > Another open issue is reference counting of memoryregions in qemu memory >>> > > model. In order to make memory hot-remove operations safe, we need to >>> > > remove >>> > > a memoryregion after all users (e.g. both guest and block layer) have >>> > > stopped >>> > > using it, >>> > >>> > it seems it mostly up to the user who want to hot-(un)plug, >>> > if user want to un-plug a memory which is kernel's main memory, kernel >>> > will always run on it(never stop) unless power off. >>> > and if guest stops, all DIMMs should be safe to hot-remove, >>> > or else we should do something to let user can unlock all reference. >>> >>> it's not only the guest-side that needs to stop using it, we need to make >>> sure >>> that the qemu block layer is also not using the memory region anymore. See >>> the 2 >>> links below for discussion: >>> >> >> can't we simply track this(MemoryRegion) usage by ref-count? >> e.g. >> every time mr used, inc ref-count, then dec it when unused >> even for cpu_physical_memory_map and other potential users. >> > > yes, that's the idea the patchset below try to implement, but last > time I checked this was not upstreamed. I will take a closer look next > week. > The current problem is that if not all the device convert to support MemoryRegionOps ref/unref API, the code in address_space_rw will be ugly. But I think the virtio data plane will need thread-safe RAM, so can we just try that for RAM device. If it is needed, I will update my patches
Regards, Pingfan >>> > > see discussion at >>> > > http://lists.gnu.org/archive/html/qemu-devel/2012-10/msg03986.html. >>> > > There was a >>> > > relevant ibm patchset >>> > > https://lists.gnu.org/archive/html/qemu-devel/2012-11/msg02697.html >>> > > but it was not merged. > > - Vasilis
