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: <5303AA97.3010202@citrix.com>
Date:	Tue, 18 Feb 2014 18:46:47 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Ian Campbell <Ian.Campbell@...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 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
(it's almost there -- it just tries to overlap the new memory with
existing stuff).

David
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