Re: [Qemu-devel] [PATCH V2 0/5] hw/pvrdma: PVRDMA device implementation

[Michael S. Tsirkin]

On Thu, Dec 21, 2017 at 05:59:38PM +0200, Marcel Apfelbaum wrote:
> On 21/12/2017 16:22, Michael S. Tsirkin wrote:
> > On Thu, Dec 21, 2017 at 09:27:51AM +0200, Yuval Shaia wrote:
> > > > > 
> > > > > > What happens if guest attempts to register all its memory?
> > > > > > 
> > > > > 
> > > > > Then we loose, is not different from bare metal, reg_mr will pin all 
> > > > > the RAM.
> > > > 
> > > > We need to find a way to communicate to guests about amount
> > > > of memory they can pin.
> > > 
> > > dev_caps.max_mr_size is the way device limits guest driver.
> > > This value is controlled by the command line argument dev-caps-max-mr-size
> > > so we should be fine (btw, default value is 1<<32).
> > 
> > Isn't that still leaving the option for guest to register all memory,
> > just in chunks?
> > 
> 
> We also have a parameter limiting the number of mrs (dev-caps-max-mr),
> together with dev-caps-max-mr-size we can limit the memory the guests can pin.
> 
> Thanks,
> Marcel

You might want to limit the default values then.

Right now:

+#define MAX_MR_SIZE           (1UL << 32)
+#define MAX_MR                2048

Which is IIUC 8TB.

That's pretty close to unlimited, and so far overcommit seems to be the
main feature for users.


> > > > 
> > > > > However this is only one scenario, and hopefully not much used
> > > > > for RoCE. (I know IPoIB does that, but it doesn't make sense to use 
> > > > > it with RoCE).
> > > > 
> > > > SRP does it too AFAIK.
> > > >