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

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Date:	Thu, 30 Jul 2015 08:26:03 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	"Michael S. Tsirkin" <mst@...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, 29 Jul 2015 18:28:26 +0300
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> 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.
considering that continuous HVA idea has failed, why would you
want to take limit back in the future if we rise it now?

> 
> 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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