Re: [PATCH] hw/net: move allocation to the heap due to very large stack frame

[Philippe Mathieu-Daudé]

On 10/12/20 1:09 PM, Philippe Mathieu-Daudé wrote:
> On 10/10/20 8:07 AM, David Gibson wrote:
> > On Fri, Oct 09, 2020 at 07:02:56AM -0700, Elena Afanasova wrote:
> > > >From 09905773a00e417d3a37c12350d9e55466fdce8a Mon Sep 17 00:00:00 2001
> > > From: Elena Afanasova <eafanasova@gmail.com>
> > > Date: Fri, 9 Oct 2020 06:41:36 -0700
> > > Subject: [PATCH] hw/net: move allocation to the heap due to very 
> > > large stack
> > >   frame
> >
> > Patch looks fine, but some more details of the motivation would be
> > nice.  I wouldn't have thought that the size of a network packet
> > counted as a "very large" stack frame by userspace standards.
>
> Maybe academia doing research on "super jumbo frames"?
>
> "Super jumbo frames ... increase the path MTU of high-performance
> national research and education networks from 1500 bytes to 9000
> bytes or so, a subsequent increase, possibly to 64,000 bytes"
>
> (https://en.wikipedia.org/wiki/Jumbo_frame#Super_jumbo_frames)

The one I was actually looking for is the IPv6 jumbogram:

"An optional feature of IPv6, the jumbo payload option, allows the 
exchange of packets with payloads of up to one byte less than 4 GiB,
by making use of a 32-bit length field."

(https://en.wikipedia.org/wiki/Jumbogram)