From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33422) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9eoc-0007ks-3F for qemu-devel@nongnu.org; Fri, 09 Jan 2015 14:01:47 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Y9eoY-0002OA-Jm for qemu-devel@nongnu.org; Fri, 09 Jan 2015 14:01:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52264) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9eoY-0002Nu-Di for qemu-devel@nongnu.org; Fri, 09 Jan 2015 14:01:42 -0500 Date: Fri, 9 Jan 2015 19:01:35 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20150109190135.GB4309@work-vm> References: <1418307457-25996-1-git-send-email-vsementsov@parallels.com> <1418307457-25996-3-git-send-email-vsementsov@parallels.com> <54AEF48F.6010405@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54AEF48F.6010405@redhat.com> Subject: Re: [Qemu-devel] [PATCH 2/9] block-migration: fix pending() return value List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow Cc: kwolf@redhat.com, "juan quin >> Juan Jose Quintela Carreira" , qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy , stefanha@redhat.com, amit Shah , den@openvz.org * John Snow (jsnow@redhat.com) wrote: > > > On 12/11/2014 09:17 AM, Vladimir Sementsov-Ogievskiy wrote: > >Because of wrong return value of .save_live_pending() in > >block-migration, migration finishes before the whole disk > >is transferred. Such situation occures when the migration > (occurs) > >process is fast enouth, for example when source and dest > (enough) > >are on the same host. > > > >If in the bulk phase we return something < max_size, we will skip > >transferring the tail of the device. Currently we have "set pending to > >BLOCK_SIZE if it is zero" for bulk phase, but there no guarantee, that > >it will be < max_size. > > > >True approach is to return, for example, max_size+1 when we are in the > >bulk phase. > > > >Signed-off-by: Vladimir Sementsov-Ogievskiy > >--- > > block-migration.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > >diff --git a/block-migration.c b/block-migration.c > >index 6f3aa18..8df30d9 100644 > >--- a/block-migration.c > >+++ b/block-migration.c > >@@ -757,8 +757,8 @@ static uint64_t block_save_pending(QEMUFile *f, void *opaque, uint64_t max_size) > > block_mig_state.read_done * BLOCK_SIZE; > > > > /* Report at least one block pending during bulk phase */ > >- if (pending == 0 && !block_mig_state.bulk_completed) { > >- pending = BLOCK_SIZE; > >+ if (pending <= max_size && !block_mig_state.bulk_completed) { > >+ pending = max_size + BLOCK_SIZE; > > } > > blk_mig_unlock(); > > qemu_mutex_unlock_iothread(); > > > > This looks sane to me, but I am CC'ing the Migration maintainers to give it > a proper look. > > Looks to me like this is to prevent this from happening, in > migration/migration.c: > > pending_size = qemu_savevm_state_pending(s->file, max_size); > trace_migrate_pending(pending_size, max_size); > if (pending_size && pending_size >= max_size) { > > If we fail that condition, we omit data because we do not call > qemu_savevm_state_iterate. Yes, I think this is safe, it doesn't feel nice, but it's safe, and I don't know of a nicer way unless that is it could calculate the actual amount of pending data. The other thing that would feel safe would be to make the _complete handler check to see if the bulk stage has completed and if it hasn't complete it. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK