> On Thu, Mar 03, 2016 at 06:44:28PM +0800, Liang Li wrote:
> > Get the free pages information through virtio and filter out the free
> > pages in the ram bulk stage. This can significantly reduce the total
> > live migration time as well as network traffic.
> >
> > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > ---
> > migration/ram.c | 52
> > ++++++++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 46 insertions(+), 6 deletions(-)
>
> > @@ -1945,6 +1971,20 @@ static int ram_save_setup(QEMUFile *f, void
> *opaque)
> > DIRTY_MEMORY_MIGRATION);
> > }
> > memory_global_dirty_log_start();
> > +
> > + if (balloon_free_pages_support() &&
> > + balloon_get_free_pages(migration_bitmap_rcu->free_pages_bmap,
> > + &free_pages_count) == 0) {
> > + qemu_mutex_unlock_iothread();
> > + while (balloon_get_free_pages(migration_bitmap_rcu-
> >free_pages_bmap,
> > + &free_pages_count) == 0) {
> > + usleep(1000);
> > + }
> > + qemu_mutex_lock_iothread();
> > +
> > + filter_out_guest_free_pages(migration_bitmap_rcu-
> >free_pages_bmap);
> > + }
>
> IIUC, this code is synchronous wrt to the guest OS balloon drive. ie it is asking
> the geust for free pages and waiting for a response. If the guest OS has
> crashed this is going to mean QEMU waits forever and thus migration won't
> complete. Similarly you need to consider that the guest OS may be malicious
> and simply never respond.
>
> So if the migration code is going to use the guest balloon driver to get info
> about free pages it has to be done in an asynchronous manner so that
> migration can never be stalled by a slow/crashed/malicious guest driver.
>
> Regards,
> Daniel
Really, thanks a lot!
Liang
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