[SK_BUFF]: Convert skb->tail to sk_buff_data_t

So that it is also an offset from skb->head, reduces its size from 8 to 4 bytes
on 64bit architectures, allowing us to combine the 4 bytes hole left by the
layer headers conversion, reducing struct sk_buff size to 256 bytes, i.e. 4
64byte cachelines, and since the sk_buff slab cache is SLAB_HWCACHE_ALIGN...
:-)

Many calculations that previously required that skb->{transport,network,
mac}_header be first converted to a pointer now can be done directly, being
meaningful as offsets or pointers.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/s390/net/ctcmain.c b/drivers/s390/net/ctcmain.c
index 787c01317042..54e3f806cd52 100644
--- a/drivers/s390/net/ctcmain.c
+++ b/drivers/s390/net/ctcmain.c
@@ -706,7 +706,8 @@ ch_action_txdone(fsm_instance * fi, int event, void *arg)
                         spin_unlock(&ch->collect_lock);
                         return;
                 }
-                ch->trans_skb->tail = ch->trans_skb->data = ch->trans_skb_data;
+                ch->trans_skb->data = ch->trans_skb_data;
+                skb_reset_tail_pointer(ch->trans_skb);
                 ch->trans_skb->len = 0;
                 if (ch->prof.maxmulti < (ch->collect_len + 2))
                         ch->prof.maxmulti = ch->collect_len + 2;
@@ -831,7 +832,8 @@ ch_action_rx(fsm_instance * fi, int event, void *arg)
                 ctc_unpack_skb(ch, skb);
         }
  again:
-        skb->data = skb->tail = ch->trans_skb_data;
+        skb->data = ch->trans_skb_data;
+        skb_reset_tail_pointer(skb);
         skb->len = 0;
         if (ctc_checkalloc_buffer(ch, 1))
                 return;
@@ -2226,7 +2228,8 @@ transmit_skb(struct channel *ch, struct sk_buff *skb)
                  * IDAL support in CTC is broken, so we have to
                  * care about skb's above 2G ourselves.
                  */
-                hi = ((unsigned long) skb->tail + LL_HEADER_LENGTH) >> 31;
+                hi = ((unsigned long)skb_tail_pointer(skb) +
+                      LL_HEADER_LENGTH) >> 31;
                 if (hi) {
                         nskb = alloc_skb(skb->len, GFP_ATOMIC | GFP_DMA);
                         if (!nskb) {
@@ -2262,7 +2265,7 @@ transmit_skb(struct channel *ch, struct sk_buff *skb)
                                 return -EBUSY;
                         }
 
-                        ch->trans_skb->tail = ch->trans_skb->data;
+                        skb_reset_tail_pointer(ch->trans_skb);
                         ch->trans_skb->len = 0;
                         ch->ccw[1].count = skb->len;
                         memcpy(skb_put(ch->trans_skb, skb->len), skb->data,