Re: [PATCH 5/5] multifd: Only sync once each full round of memory

[Juan Quintela]

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Juan Quintela (quintela@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 <quintela@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.

Later, Juan.

> 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).

It looks worse to me.

Later, Juan.

> It feels like you could have done that in the previous patch.
> Anyway,
>
>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Thanks, Juan.