Re: [PATCH 4/5] migration: Disallow postcopy preempt to be used with compress

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> The preempt mode requires the capability to assign channel for each of the
> page, while the compression logic will currently assign pages to different
> compress thread/local-channel so potentially they're incompatible.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index fb4066dfb4..07c74a79a2 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1341,6 +1341,17 @@ static bool migrate_caps_check(bool *cap_list,
>              error_setg(errp, "Postcopy preempt requires postcopy-ram");
>              return false;
>          }
> +
> +        /*
> +         * Preempt mode requires urgent pages to be sent in separate
> +         * channel, OTOH compression logic will disorder all pages into
> +         * different compression channels, which is not compatible with the
> +         * preempt assumptions on channel assignments.
> +         */
> +        if (cap_list[MIGRATION_CAPABILITY_COMPRESS]) {
> +            error_setg(errp, "Postcopy preempt not compatible with compress");
> +            return false;
> +        }
>      }
>  
>      return true;
> -- 
> 2.32.0
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK