Re: Re: [libvirt PATCH 1/3] Introduce VIR_MIGRATE_POSTCOPY_PREEMPT flag

On Fri, Jan 5, 2024 at 4:55 PM Jiri Denemark <jdenemar(a)redhat.com&gt; wrote: > During post-copy migration (once it actually switches to post-copy mode) > dirty memory pages are continued to be migrated iteratively, while the > destination can explicitly request a specific page to be migrated before > the iterative process gets to it (which happens when a guest wants to > read a page that was not migrated yet). Without this flag explicitly > requested pages need to wait until all other pages already queued are > transferred. Enabling this flag will instruct the hypervisor to create a > separate migration channel for explicitly requested pages so that they > can preempt the queue. > > Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; > --- > include/libvirt/libvirt-domain.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/libvirt/libvirt-domain.h > b/include/libvirt/libvirt-domain.h > index 30cce85b29..ee23ae97a5 100644 > --- a/include/libvirt/libvirt-domain.h > +++ b/include/libvirt/libvirt-domain.h > @@ -1100,6 +1100,14 @@ typedef enum { > * Since: 8.5.0 > */ > VIR_MIGRATE_ZEROCOPY = (1 << 20), > + > + /* Allow post-copy requests to preempt normal migration stream. This > way > + * page faults on the destination hosts caused by accessing a memory > page > + * that was not migrated yet should be handled faster. > > Based on this description and the commit message there doesn't seem to be any reason why the user should not enable that. And in that case I think the users will be better off when libvirt auto-enables this.