Re: [Libguestfs] [PATCH v3 0/3] v2v: simplify driver copying from virtio-win iso

On Thu, Oct 15, 2015 at 12:27:58PM +0300, Roman Kagan wrote: > On Thu, Oct 15, 2015 at 10:07:45AM +0100, Richard W.M. Jones wrote: > > On Wed, Oct 14, 2015 at 07:55:41PM +0300, Roman Kagan wrote: > > > Libguestfs supports passing an ISO image as a source of virtio windows > > > drivers to v2v. > > > > > > This series attempts to make it simpler and better scoped. > > > > Looks good (apart from patch 3 - the Gc.compact is necessary!) > > Why? As a matter of fact that was the primary reason I even started > with this patchset: that Gc.compact was sitting in the middle of the > main v2v function and was yet another obstacle in the refactoring I was > after. > > Now that the extra guestfs handle doesn't survive beyond > copy_virtio_drivers() what is the need for that explicit GC (which was > introduced at the time exactly to clear up that handle in commit > 47b5f245bec908f803f0a89c3b1e3166cfe33aad)? Just because the handle becomes unreachable doesn't mean the GC will immediately collect it. Objects are only required to be finalized when you invoke Gc.full_major (Gc.compact calls Gc.full_major). Previous to these patches, the handle was still unreachable, but Gc.compact didn't free it because of a different problem. That different issue has been fixed by: https://github.com/libguestfs/libguestfs/commit/8bbc5e73cb5b56b5cfbe979ac... In summary, we still need to call Gc.compact before doing the long-running copy operation, to make sure that the resources used by virt-v2v are minimized during the copy.