[Qemu-devel] 答复: Re: [PATCH] vhost: fix a migration failed because ofvhost region merge

[<peng.hao2@zte.com.cn>]

发件人： <imammedo@redhat.com>
收件人：彭浩10096742
抄送人： <mst@redhat.com>王业超10154425 <qemu-devel@nongnu.org>
日 期 ：2017年07月19日 15:51
主 题 ：Re: [Qemu-devel] [PATCH] vhost: fix a migration failed because ofvhost region merge





On Wed, 19 Jul 2017 23:17:32 +0800
Peng Hao <peng.hao2@zte.com.cn> wrote:

> When a guest that has several hotplugged dimms is migrated, in
> destination host it will fail to resume. Because vhost regions of
> several dimms in source host are merged and in the restore stage
> in destination host it computes whether more than vhost slot limit
> before merging vhost regions of several dimms.
could you provide a bit more detailed description of the problem
including command line+used device_add commands on source and
command line on destination?

-------I just migrate guest vm. The guest has vhost-user net. Vhost-user has a limit of slots

 (VHOST_MEMORY_MAX_NREGIONS=8),hotplug memory (dimm) can increase vhost used slots

,but vhost can merge region to decrease vhost used slots.

Before migration guset has hotplugged  several dimms one by one (more than vhost slot limit,

but after merging it less than  vhost slot limit). In migrating to destination host ,qemu begins to 

execute restore guest and it realize  foreach  dimms device at a time and 


compute whether vhost used slots more than vhost slot limit before merging.


So report "a used vhost backend has no free  memory slots left".


I just make a distinction using a vm state.

> 
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> Signed-off-by: Wang Yechao <wang.yechao255@zte.com.cn>
> ---
>  hw/mem/pc-dimm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
> index ea67b46..bb0fa08 100644
> --- a/hw/mem/pc-dimm.c
> +++ b/hw/mem/pc-dimm.c
> @@ -101,7 +101,7 @@ void pc_dimm_memory_plug(DeviceState *dev, MemoryHotplugState *hpms,
>          goto out
>      }
>  
> -    if (!vhost_has_free_slot()) {
> +    if (!vhost_has_free_slot() && runstate_is_running()) {
>          error_setg(&local_err, "a used vhost backend has no free"
>                                 " memory slots left")
>          goto out