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

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Date:	Wed, 29 Jul 2015 18:28:26 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, pbonzini@...hat.com,
	kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] vhost: increase default limit of nregions from 64 to
 509

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@...hat.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
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