Re: [Xen-devel] [PATCH net-next v2 2/9] xen-netback: Change TX pathfrom grant copy to mapping

[Zoltan Kiss]

On 17/12/13 21:49, Konrad Rzeszutek Wilk wrote:
> On Thu, Dec 12, 2013 at 11:48:10PM +0000, Zoltan Kiss wrote:
> > @@ -485,6 +520,22 @@ void xenvif_disconnect(struct xenvif *vif)
> >
> >   void xenvif_free(struct xenvif *vif)
> >   {
> > +	int i, unmap_timeout = 0;
> > +
> > +	for (i = 0; i < MAX_PENDING_REQS; ++i) {
> > +		if (vif->grant_tx_handle[i] != NETBACK_INVALID_HANDLE) {
> > +			i = 0;
> > +			unmap_timeout++;
> > +			msleep(1000);
>
> You don't want to use schedule() and a wakeup here to allow other threads
> to do their work?
Yep, schedule_timeout() would be nicer indeed

> > +			if (unmap_timeout > 9 &&
> > +				net_ratelimit())
> > +				netdev_err(vif->dev,
> > +					"Page still granted! Index: %x\n", i);
> > +		}
> > +	}
> > +
> > +	free_xenballooned_pages(MAX_PENDING_REQS, vif->mmap_pages);
>
> How about just stashing those pages on a 'I can't free them' list that will
> keep them forever. And if that list gets truly large then switch back to
> grant_copy?
But then what would you answer to the guest? You can't shoot the shared 
ring until there is an outstanding slot.
On the other hand, doing a copy would just move the memory leak into the 
backend, which could be problematic if a guest figures out how to make a 
packet which can get stucked somewhere in the backend.

Zoli
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