Re: [PATCH 1/3] migration: In case of postcopy, the memory ends in res_postcopy_only

[Juan Quintela]

Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> wrote:
> On 08.02.23 16:57, Juan Quintela wrote:
>> So remove last assignation of res_compatible.
>
> I hoped for some description when asked to split it out :)
>
>> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> ---
>>   migration/ram.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/migration/ram.c b/migration/ram.c
>> index b966e148c2..85ccbf88ad 100644
>> --- a/migration/ram.c
>> +++ b/migration/ram.c
>> @@ -3474,7 +3474,7 @@ static void ram_state_pending_exact(void *opaque,
>>         if (migrate_postcopy_ram()) {
>>           /* We can do postcopy, and all the data is postcopiable */
>> -        *res_compatible += remaining_size;
>> +        *res_postcopy_only += remaining_size;
>
> Actually, these "remaining_size" bytes are still compatible, i.e. we
> can migrate these pending bytes in pre-copy, and we actually do it,
> until user call migrate-start-postcopy, yes? But we exploit the fact
> that, this change don't affect any logic, just name becomes
> wrong.. Yes? Or I don't follow:/

I think of this from this different angle:
- if we are on precopy, we return on res_precopy everything (and nothing
  on res_postcopy)
- if we are on postcopy, we return on res_precopy what we _must_ sent
  through precopy, and in res_postcopy what we can sent through
  postcopy.

i.e. if we stop the guest and do the migration right now, what are we
going to send through each channel.

Later, Juan.