Re: [Qemu-devel] [PATCH v2 02/16] postcopy: Transmit and compare individual page sizes

[Laurent Vivier]

On 06/02/2017 18:32, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> When using postcopy with hugepages, we require the source
> and destination page sizes for any RAMBlock to match; note
> that different RAMBlocks in the same VM can have different
> page sizes.
> 
> Transmit them as part of the RAM information header and
> fail if there's a difference.
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  migration/ram.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index b405e4a..5726563 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1979,6 +1979,9 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>          qemu_put_byte(f, strlen(block->idstr));
>          qemu_put_buffer(f, (uint8_t *)block->idstr, strlen(block->idstr));
>          qemu_put_be64(f, block->used_length);
> +        if (migrate_postcopy_ram() && block->page_size != 
> qemu_host_page_size) {
> +            qemu_put_be64(f, block->page_size);
> +        }

I understand we don't break migration to previous machine type by adding
data in the migration stream because migration is already broken when
block->page_size != qemu_host_page_size. Am I correct?

Laurent