Use of contiguous physical memory in cxgbe driver

[Scott Long]

On Feb 13, 2014, at 10:07 AM, John-Mark Gurney <jmg at funkthat.com> wrote:

> Garrett Wollman wrote this message on Thu, Feb 13, 2014 at 12:44 -0500:
>> <<On Wed, 12 Feb 2014 23:56:51 -0800, John-Mark Gurney <jmg at funkthat.com> said:
>> 
>>> Though we might want to keep a few mbufs reserved for receive now that
>>> you mention it...  We should never get to the point where we can't
>>> allocate even one frame for receive...
>> 
>> It's very easy to get to that state if the driver insists on getting
>> three physically contiguous pages (which is what it takes to allocate
>> a single 9k cluster)
> 
> Well, if you're using a cheap NIC that can't do scatter/gather DMA,
> then you get what you pay for…
> 

Like I alluded to in another email, it’s not a hard problem to address for these
“cheap” cards, it’s a deliberate design decision from FreeBSD.

Scott