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

On Fri, Jan 05, 2024 at 17:11:57 +0100, Peter Krempa wrote: > 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. Well yes, ideally you want this enabled all the time. But Peter Xu did not sound like it was ready for being always enabled. I guess I'll check with him if it's still the case or not.