Re: [PATCH v4 22/23] migration: Use multifd before we check for the zero page

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

* Juan Quintela (quintela@redhat.com) wrote:
> So we use multifd to transmit zero pages.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 3536778e19..bdc7cec4cd 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2168,6 +2168,32 @@ static int ram_save_target_page_legacy(RAMState *rs, PageSearchStatus *pss)
>      return ram_save_page(rs, pss);
>  }
>  
> +/**
> + * ram_save_target_page_multifd: save one target page
> + *
> + * Returns the number of pages written
> + *
> + * @rs: current RAM state
> + * @pss: data about the page we want to send
> + */
> +static int ram_save_target_page_multifd(RAMState *rs, PageSearchStatus *pss)
> +{
> +    RAMBlock *block = pss->block;
> +    ram_addr_t offset = ((ram_addr_t)pss->page) << TARGET_PAGE_BITS;
> +    int res;
> +
> +    if (!migration_in_postcopy()) {
> +        return ram_save_multifd_page(rs, block, offset);
> +    }
> +
> +    res = save_zero_page(rs, block, offset);

I'm confused; I think I was expecting to see in this patch, the one that
would check the parameter you added and do something different - where
did that go?

Note I think this is quite subtle that the difference here is really
just the ordering rather than adding a zero page test.

Dave

> +    if (res > 0) {
> +        return res;
> +    }
> +
> +    return ram_save_page(rs, pss);
> +}
> +
>  /**
>   * ram_save_host_page: save a whole host page
>   *
> @@ -3011,7 +3037,11 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>      ram_control_before_iterate(f, RAM_CONTROL_SETUP);
>      ram_control_after_iterate(f, RAM_CONTROL_SETUP);
>  
> -    (*rsp)->ram_save_target_page = ram_save_target_page_legacy;
> +    if (migrate_use_multifd()) {
> +        (*rsp)->ram_save_target_page = ram_save_target_page_multifd;
> +    } else {
> +        (*rsp)->ram_save_target_page = ram_save_target_page_legacy;
> +    }
>      multifd_send_sync_main(f);
>      qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
>      qemu_fflush(f);
> -- 
> 2.34.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK