Re: [Qemu-devel] [01/15] postcopy: Transmit and compare individual page sizes

[Alexey Perevalov <a.perevalov@samsung.com>]

Hi David,

I checked you whole patch set with Andrea's kernel
git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git

It works and really gives sufficient decreasing of the downtime.

I'm newby in qemu and here in the mailing list.

I have some remarks on current patch.

On both client and server side post copy capability should be enabled

migrate_set_capability postcopy-ram on

and serialization/deserialization relies on it.

  So if destination host
doesn't set post copy capability ram_load will skip reading of
remote_page_size and in case of multiple RAMBlocks the next read of len
will be incorrect. Hopefully usually len is 0, but it could be bigger 
and overrun buffer ;).
Maybe it's better to pass post copy capability attribute from host to 
destination to avoid
such assumption.


On 01/06/2017 09:28 PM, Dave Gilbert wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> When using postcopy with hugepages, we require the source
> and destination page sizes for any RAMBlock to match.
>
> Transmit them as part of the RAM information header and
> fail if there's a difference.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>   migration/ram.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index a1c8089..39998f5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1970,6 +1970,9 @@ 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);
> +        }
>       }
>   
>       rcu_read_unlock();
> @@ -2536,6 +2539,18 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                               error_report_err(local_err);
>                           }
>                       }
> +                    /* For postcopy we need to check hugepage sizes match */
> +                    if (migrate_postcopy_ram() &&
> +                        block->page_size != qemu_host_page_size) {
> +                        uint64_t remote_page_size = qemu_get_be64(f);
> +                        if (remote_page_size != block->page_size) {
> +                            error_report("Mismatched RAM page size %s "
> +                                         "(local) %" PRId64 "!= %" PRId64,
> +                                         id, block->page_size,
> +                                         remote_page_size);
> +                            ret = -EINVAL;
> +                        }
> +                    }
>                       ram_control_load_hook(f, RAM_CONTROL_BLOCK_REG,
>                                             block->idstr);
>                   } else {


-- 
Best regards,
Alexey Perevalov