Re: [PATCH v2 13/16] migration: Remember total dirty bytes in mig_stats

[Juraj Marcin <jmarcin@redhat.com>]

On 2026-04-21 16:21, Peter Xu wrote:
> Introduce this new counter to remember the total dirty bytes for the whole
> system.  It will be used for query-migrate command to fetch system-wise
> remaining data.
> 
> A prior attempt was made to not use this counter but query directly from
> all the modules in a QMP handler, but it exposed some complexity not only
> on migration state machine race conditions (where the query may be invoked
> anytime of the state machine), or on locking implications (where some of
> the query hooks may take BQL, which is illegal at least in a QMP handler).
> For more information, see:
> 
> https://lore.kernel.org/r/aeZMtxqrKWAMKzdN@x1.local
> 
> This oneliner will resolve everything, except that it is not as accurate.
> The hope is it is a worthwhile trade-off solution, after knowing above
> challenges.
> 
> Now, there is one more reason we should make each invocation of
> save_live_iterate() to be lightweight, because this counter will only get
> updated once for each loop over all save_live_iterate() hooks when present.
> But that's always the goal.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/migration-stats.h | 7 +++++++
>  migration/savevm.c          | 7 +++++++
>  2 files changed, 14 insertions(+)

Reviewed-by: Juraj Marcin <jmarcin@redhat.com>