Linux Virtualization - Aug 2019 - [PATCH V2 7/9] vhost: do not use RCU to synchronize MMU notifier with worker

On Sun, Aug 04, 2019 at 04:07:17AM -0400, Michael S. Tsirkin
wrote:
> > > > Also, why can't this just permanently GUP the pages? In
fact, where
> > > > does it put_page them anyhow? Worrying that 7f466 adds a
get_user page
> > > > but does not add a put_page??
> > 
> > You didn't answer this.. Why not just use GUP?
> > 
> > Jason
> 
> Sorry I misunderstood the question. Permanent GUP breaks lots of
> functionality we need such as THP and numa balancing.
Really? It doesn't look like that many pages are involved..

Jason

On Tue, Aug 06, 2019 at 08:53:17AM -0300, Jason Gunthorpe
wrote:
> On Sun, Aug 04, 2019 at 04:07:17AM -0400, Michael S. Tsirkin wrote:
> > > > > Also, why can't this just permanently GUP the
pages? In fact, where
> > > > > does it put_page them anyhow? Worrying that 7f466 adds
a get_user page
> > > > > but does not add a put_page??
> > > 
> > > You didn't answer this.. Why not just use GUP?
> > > 
> > > Jason
> > 
> > Sorry I misunderstood the question. Permanent GUP breaks lots of
> > functionality we need such as THP and numa balancing.
> 
> Really? It doesn't look like that many pages are involved..
> 
> Jason
Yea. But they just might happen to be heavily accessed ones....

-- 
MST

On Tue, Aug 06, 2019 at 09:36:58AM -0400, Michael S. Tsirkin
wrote:
> On Tue, Aug 06, 2019 at 08:53:17AM -0300, Jason Gunthorpe wrote:
> > On Sun, Aug 04, 2019 at 04:07:17AM -0400, Michael S. Tsirkin wrote:
> > > > > > Also, why can't this just permanently GUP the
pages? In fact, where
> > > > > > does it put_page them anyhow? Worrying that 7f466
adds a get_user page
> > > > > > but does not add a put_page??
> > > > 
> > > > You didn't answer this.. Why not just use GUP?
> > > > 
> > > > Jason
> > > 
> > > Sorry I misunderstood the question. Permanent GUP breaks lots of
> > > functionality we need such as THP and numa balancing.
> > 
> > Really? It doesn't look like that many pages are involved..
> > 
> > Jason
> 
> Yea. But they just might happen to be heavily accessed ones....
Maybe you can solve the numa balance problem some other way and use
normal GUP..

Jason