Re: [PATCH v4 0/4] migration/postcopy: Sync faulted addresses after network recovered

[Dr. David Alan Gilbert]

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> Queued

Hi Peter,
  I've had to unqueue this again unfortunately.
There's something going on with big endian hosts; on a PPC BE host,
it reliably hangs in the recovery test with this set.
(Although I can't see anything relevant to eye).

Dave
P.S. I can point you at an installed host

> * Peter Xu (peterx@redhat.com) wrote:
> > v4:
> > - use "void */ulong" instead of "uint64_t" where proper in patch 3/4 [Dave]
> > 
> > v3:
> > - fix build on 32bit hosts & rebase
> > - remove r-bs for the last 2 patches for Dave due to the changes
> > 
> > v2:
> > - add r-bs for Dave
> > - add patch "migration: Properly destroy variables on incoming side" as 
> > patch 1
> > - destroy page_request_mutex in migration_incoming_state_destroy() too 
> > [Dave]
> > - use WITH_QEMU_LOCK_GUARD in two places where we can [Dave]
> > 
> > We've seen conditional guest hangs on destination VM after postcopy 
> > recovered.
> > However the hang will resolve itself after a few minutes.
> > 
> > The problem is: after a postcopy recovery, the prioritized postcopy queue on
> > the source VM is actually missing.  So all the faulted threads before the
> > postcopy recovery happened will keep halted until (accidentally) the page 
> > got
> > copied by the background precopy migration stream.
> > 
> > The solution is to also refresh this information after postcopy recovery.  
> > To
> > achieve this, we need to maintain a list of faulted addresses on the
> > destination node, so that we can resend the list when necessary.  This work 
> > is
> > done via patch 2-5.
> > 
> > With that, the last thing we need to do is to send this extra information to
> > source VM after recovered.  Very luckily, this synchronization can be
> > "emulated" by sending a bunch of page requests (although these pages have 
> > been
> > sent previously!) to source VM just like when we've got a page fault.  Even 
> > in
> > the 1st version of the postcopy code we'll handle duplicated pages well.  So
> > this fix does not even need a new capability bit and it'll work smoothly on 
> > old
> > QEMUs when we migrate from them to the new QEMUs.
> > 
> > Please review, thanks.
> > 
> > Peter Xu (4):
> >   migration: Pass incoming state into qemu_ufd_copy_ioctl()
> >   migration: Introduce migrate_send_rp_message_req_pages()
> >   migration: Maintain postcopy faulted addresses
> >   migration: Sync requested pages after postcopy recovery
> > 
> >  migration/migration.c    | 49 ++++++++++++++++++++++++++++++++--
> >  migration/migration.h    | 21 ++++++++++++++-
> >  migration/postcopy-ram.c | 25 +++++++++++++-----
> >  migration/savevm.c       | 57 ++++++++++++++++++++++++++++++++++++++++
> >  migration/trace-events   |  3 +++
> >  5 files changed, 146 insertions(+), 9 deletions(-)
> > 
> > -- 
> > 2.26.2
> > 
> > 
> > 
> -- 
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK