Re: compound skb frag pages appearing in start_xmit

On Tue, 2012-10-09 at 15:40 +0100, Ian Campbell wrote:

On Tue, 2012-10-09 at 15:27 +0100, Eric Dumazet wrote:

quoted

On Tue, 2012-10-09 at 15:17 +0100, Ian Campbell wrote:

quoted

Does the higher order pages effectively reduce the number of frags which
are in use? e.g if MAX_SKB_FRAGS is 16, then for order-0 pages you could
have 64K worth of frag data.

If we switch to order-3 pages everywhere then can the skb contain 512K
of data, or does the effective maximum number of frags in an skb reduce
to 2?

effective number of frags reduce to 2 or 3

(We still limit GSO packets to ~63536 bytes)

Great! Then I think the fix is more/less trivial...

As an aside, when the skb head is < 4096 bytes is that necessarily a
compound page or might it just be a large kmalloc area?

skb->head can be either allocated by kmalloc() (standard alloc_skb()) or
a page frag (if allocated in rx path)

Not sure its related to headlen/size...