Re: [Qemu-devel] [PATCH 0/2] vhost: two fixes

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Zhoujian (jay) (jianjay.zhou@huawei.com) wrote:
> Hi Dave,
> 
> > -----Original Message-----
> > From: Dr. David Alan Gilbert [mailto:dgilbert@redhat.com]
> > Sent: Friday, December 15, 2017 3:49 AM
> > To: Michael S. Tsirkin <mst@redhat.com>
> > Cc: Zhoujian (jay) <jianjay.zhou@huawei.com>; qemu-devel@nongnu.org;
> > Huangweidong (C) <weidong.huang@huawei.com>; Gonglei (Arei)
> > <arei.gonglei@huawei.com>; wangxin (U) <wangxinxin.wang@huawei.com>;
> > Liuzhe (Cloud Open Labs, NFV) <gary.liuzhe@huawei.com>; Igor Mammedov
> > <imammedo@redhat.com>
> > Subject: Re: [PATCH 0/2] vhost: two fixes
> > 
> > * Michael S. Tsirkin (mst@redhat.com) wrote:
> > > On Fri, Dec 15, 2017 at 12:36:30AM +0800, Jay Zhou wrote:
> > > > Jay Zhou (2):
> > > >   vhost: add used memslot number for vhost-user
> > > >   vhost: double check memslot number
> > > >
> > > >  hw/virtio/vhost-user.c            | 31 +++++++++++++++++++++++++
> > > >  hw/virtio/vhost.c                 | 49
> > ++++++++++++++++++++++++++++++++++-----
> > > >  include/hw/virtio/vhost-backend.h |  4 ++++
> > > >  3 files changed, 78 insertions(+), 6 deletions(-)
> > >
> > > Cc two developers working on these files right now.
> > 
> > I have to admit to not understanding the 'used_memslots' variable.
> > 
> > * It's a global in vhost.c
> > * but set by vhost_set_memory that's called from the listener associated
> >   with each individual vhost
> > * While they're probably always the same, the merging code calls
> >   the vhost_backend_can_merge method for each device, so the number
> >   of regions can be different.
> > 
> 
> Your mean for some devices the new added MemoryRegionSection can be merged,
> but for others it can not be merged?

That's my understanding, because of the call to vhost_backend_can_merge

> IIUC the vhost_mem for each vhost_dev
> is the same.
> 
> Meanwhile, I think it is more reasonable to add globals in vhost-backend.c
> and vhost-user.c respectively instead of 'used_memslots'. The reason
> is explained in patch 1. What do you think?

If we need globals I'm not sure it matters that much where they live.

Dave

> Regards,
> Jay
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK