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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

Queued

* 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