Re: [Xen-devel] [PATCH net-next v5 2/9] xen-netback: Change TX path from grant copy to mapping

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-02-18 at 18:46 +0000, David Vrabel wrote:
> On 18/02/14 17:40, Ian Campbell wrote:
> > On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote:
> >> 
> >> @@ -344,8 +346,26 @@ struct xenvif *xenvif_alloc(struct device *parent, 
> >> domid_t domid,
> >>    vif->pending_prod = MAX_PENDING_REQS;
> >>    for (i = 0; i < MAX_PENDING_REQS; i++)
> >>            vif->pending_ring[i] = i;
> >> -  for (i = 0; i < MAX_PENDING_REQS; i++)
> >> -          vif->mmap_pages[i] = NULL;
> >> +  spin_lock_init(&vif->dealloc_lock);
> >> +  spin_lock_init(&vif->response_lock);
> >> +  /* If ballooning is disabled, this will consume real memory, so you
> >> +   * better enable it.
> > 
> > Almost no one who would be affected by this is going to read this
> > comment. And it doesn't just require enabling ballooning, but actually
> > booting with some maxmem "slack" to leave space.
> > 
> > Classic-xen kernels used to add 8M of slop to the physical address space
> > to leave a suitable pool for exactly this sort of thing. I never liked
> > that but perhaps it should be reconsidered (or at least raised as a
> > possibility with the core-Xen Linux guys).
> 
> I plan to fix the balloon memory hotplug stuff to do the right thing

Which is for alloc_xenballoon_pages to hotplug a new empty region,
rather than inflating the balloon if it doesn't have enough pages to
satisfy the allocation? Or something else?

> (it's almost there -- it just tries to overlap the new memory with
> existing stuff).
> 
> David



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