linux-kernel - Re: [PATCH 3/5] vhost: support upto 509 memory regions

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Date:	Wed, 17 Jun 2015 00:00:56 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	pbonzini@...hat.com
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions

On Tue, 16 Jun 2015 23:14:20 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Tue, Jun 16, 2015 at 06:33:37PM +0200, Igor Mammedov wrote:
> > since commit
> >  1d4e7e3 kvm: x86: increase user memory slots to 509
> > 
> > it became possible to use a bigger amount of memory
> > slots, which is used by memory hotplug for
> > registering hotplugged memory.
> > However QEMU crashes if it's used with more than ~60
> > pc-dimm devices and vhost-net since host kernel
> > in module vhost-net refuses to accept more than 65
> > memory regions.
> > 
> > Increase VHOST_MEMORY_MAX_NREGIONS from 65 to 509
> 
> It was 64, not 65.
> 
> > to match KVM_USER_MEM_SLOTS fixes issue for vhost-net.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@...hat.com>
> 
> Still thinking about this: can you reorder this to
> be the last patch in the series please?
sure

> 
> Also - 509?
userspace memory slots in terms of KVM, I made it match
KVM's allotment of memory slots for userspace side.

> I think if we are changing this, it'd be nice to
> create a way for userspace to discover the support
> and the # of regions supported.
That was my first idea before extending KVM's memslots
to teach kernel to tell qemu this number so that QEMU
at least would be able to check if new memory slot could
be added but I was redirected to a more simple solution
of just extending vs everdoing things.
Currently QEMU supports upto ~250 memslots so 509
is about twice high we need it so it should work for near
future but eventually we might still teach kernel and QEMU
to make things more robust.

> 
> 
> > ---
> >  drivers/vhost/vhost.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 99931a0..6a18c92 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -30,7 +30,7 @@
> >  #include "vhost.h"
> >  
> >  enum {
> > -	VHOST_MEMORY_MAX_NREGIONS = 64,
> > +	VHOST_MEMORY_MAX_NREGIONS = 509,
> >  	VHOST_MEMORY_F_LOG = 0x1,
> >  };
> >  
> > -- 
> > 1.8.3.1

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