[Xen-API] [Xen-devel] Is: SKB_MAX_LEN bites again. Was: Re: bug disabling guest interface

[Brian Menges <bmenges@xxxxxxxxxx>]

Seems I'm completely bitten by this as well. I did notice one difference though 
between our old production kernel, and the new one that I'm trying to run 
(Linux 3.8.6)

Looking into sources for 3.2.14-gogrid, I see:
struct sk_buff;

/* To allow 64K frame to be packed as single skb without frag_list. Since
* GRO uses frags we allocate at least 16 regardless of page size.
*/
#if (65536/PAGE_SIZE + 2) < 16
#define MAX_SKB_FRAGS 16UL
#else
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)
#endif

Looking into sources for 3.8.6-gogrid I see:
struct sk_buff;

/* To allow 64K frame to be packed as single skb without frag_list we
* require 64K/PAGE_SIZE pages plus 1 additional page to allow for
* buffers which do not start on a page boundary.
*
* Since GRO uses frags we allocate at least 16 regardless of page
* size.
*/
#if (65536/PAGE_SIZE + 1) < 16
#define MAX_SKB_FRAGS 16UL
#else
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
#endif

I'm supposing that we could change both instances of '+1' to '+2' and see if 
this temporarily patches us until netback (???) is patched up.

- Brian Menges
Principal Engineer, DevOps
GoGrid | ServePath | ColoServe | UpStream Networks

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