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

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Message-ID: <1392803670.23084.100.camel@kazak.uk.xensource.com>
Date:	Wed, 19 Feb 2014 09:54:30 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Zoltan Kiss <zoltan.kiss@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <jonathan.davies@...rix.com>,
	<wei.liu2@...rix.com>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH net-next v5 2/9] xen-netback: Change TX path
 from grant copy to mapping

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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