mlx5(4) jumbo receive

[Rick Macklem]

Ryan Stone wrote:
>On Tue, Apr 24, 2018 at 4:55 AM, Konstantin Belousov >><kostikbel at gmail.com>wrote:
>> +#ifndef MLX5E_MAX_RX_BYTES
>> +#define        MLX5E_MAX_RX_BYTES MCLBYTES
>> +#endif
>
>Why do you use a 2KB buffer rather than a PAGE_SIZE'd buffer?
>MJUMPAGESIZE should offer significantly better performance for jumbo
>frames without increasing the risk of memory fragmentation.
Actually, when I was playing with using jumbo mbuf clusters for NFS, I was able
to get it to fragment to the point where allocations failed when mixing 2K and
4K mbuf clusters.
Admittedly I was using a 256Mbyte i386 and it wasn't easily reproduced, but
it was possible.
--> Using a mix of 2K and 4K mbuf clusters can result in fragmentation, although
      I suspect that it isn't nearly as serious as what can happen when using 9K
      mbuf clusters.

rick