On Tue, Jul 05, 2022 at 05:11:46PM +0200, Juan Quintela wrote:
> "Dr. David Alan Gilbert" <dgilb...@redhat.com> wrote:
> > * Juan Quintela (quint...@redhat.com) wrote:
> >> We need to add a new flag to mean to sync at that point.
> >> Notice that we still synchronize at the end of setup and at the end of
> >> complete stages.
> >>
> >> Signed-off-by: Juan Quintela <quint...@redhat.com>
> >> ---
> >> migration/migration.c | 2 +-
> >> migration/ram.c | 42 ++++++++++++++++++++++++++++++------------
> >> 2 files changed, 31 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/migration/migration.c b/migration/migration.c
> >> index 3f79df0b70..6627787fc2 100644
> >> --- a/migration/migration.c
> >> +++ b/migration/migration.c
> >> @@ -4283,7 +4283,7 @@ static Property migration_properties[] = {
> >> DEFAULT_MIGRATE_ANNOUNCE_STEP),
> >> /* We will change to false when we introduce the new mechanism */
> >> DEFINE_PROP_BOOL("multifd-sync-each-iteration", MigrationState,
> >> - multifd_sync_each_iteration, true),
> >> + multifd_sync_each_iteration, false),
> >>
> >> /* Migration capabilities */
> >> DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
> >> diff --git a/migration/ram.c b/migration/ram.c
> >> index 2c7289edad..6792986565 100644
> >> --- a/migration/ram.c
> >> +++ b/migration/ram.c
> >> @@ -81,6 +81,7 @@
> >> #define RAM_SAVE_FLAG_XBZRLE 0x40
> >> /* 0x80 is reserved in migration.h start with 0x100 next */
> >> #define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100
> >> +#define RAM_SAVE_FLAG_MULTIFD_SYNC 0x200
> >
> > Note this is the very last usable flag!
>
> We can recover two flags right now:
>
> RAM_SAVE_FLAG_FULL is not used anymore.
> 0x80 is free since years ago.
>
> Once multifd is default, there are some other that could go.
Non-multifd migration isn't likely to go away any time soon, given
distros desire to support migration between QEMU's with quite
significantly different versions. So feels like quite a long time
before we might reclaim more flags.
> > We could do with avoiding using them as flags where we dont need to.
>
> I can't really think on another way to do it. The other thing that I
> can do is just reuse one of the flags that don't make sense for multifd
> (RAM_SAVE_FLAG_ZERO after zero pages patch,
> RAM_SAVE_FLAG_XBZRLE/COMPRESS_PAGE).
Re-using flags based on use context differences feels like a recipe
to confuse people.
With regards,
Daniel
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