Re: [PATCH 2/2] vhost: increase default limit of nregions from 64 to 509

Michael S. Tsirkin
2015-07-29T15:28:31Z

On Wed, Jul 29, 2015 at 04:29:23PM +0200, Igor Mammedov wrote:
> although now there is vhost module max_mem_regions option
> to set custom limit it doesn't help for default setups,
> since it requires administrator manually set a higher
> limit on each host. Which complicates servers deployments
> and management.
> Rise limit to the same value as KVM has (509 slots max),
> so that default deployments would work out of box.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> PS:
> Users that would want to lock down vhost could still
> use max_mem_regions option to set lower limit, but
> I expect it would be minority.

I'm not inclined to merge this.

Once we change this we can't take it back. It's not a decision
to be taken lightly.

And memory hotplug users are a minority. Out of these, users with a
heavily fragmented PA space due to hotplug abuse are an even smaller
minority.

> ---
> include/uapi/linux/vhost.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index 2511954..92657bf 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -140,7 +140,7 @@ struct vhost_memory {
> #define VHOST_MEM_MAX_NREGIONS_NONE 0
> /* We support at least as many nregions in VHOST_SET_MEM_TABLE:
> * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */
> -#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64
> +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 509
>
> /* VHOST_NET specific defines */
>
> --
> 1.8.3.1