[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>

2 files changed, 13 insertions, 8 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,
diff --git a/drivers/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
index 82edf2014402..cd42bd54988c 100644
--- a/drivers/s390/net/netiucv.c
+++ b/drivers/s390/net/netiucv.c
@@ -689,7 +689,8 @@ static void conn_action_rx(fsm_instance *fi, int event, void *arg)
                                msg->length, conn->max_buffsize);
                 return;
         }
-        conn->rx_buff->data = conn->rx_buff->tail = conn->rx_buff->head;
+        conn->rx_buff->data = conn->rx_buff->head;
+        skb_reset_tail_pointer(conn->rx_buff);
         conn->rx_buff->len = 0;
         rc = iucv_message_receive(conn->path, msg, 0, conn->rx_buff->data,
                                   msg->length, NULL);
@@ -735,7 +736,8 @@ static void conn_action_txdone(fsm_instance *fi, int event, void *arg)
                         }
                 }
         }
-        conn->tx_buff->data = conn->tx_buff->tail = conn->tx_buff->head;
+        conn->tx_buff->data = conn->tx_buff->head;
+        skb_reset_tail_pointer(conn->tx_buff);
         conn->tx_buff->len = 0;
         spin_lock_irqsave(&conn->collect_lock, saveflags);
         while ((skb = skb_dequeue(&conn->collect_queue))) {
@@ -1164,8 +1166,8 @@ static int netiucv_transmit_skb(struct iucv_connection *conn,
                  * Copy the skb to a new allocated skb in lowmem only if the
                  * data is located above 2G in memory or tailroom is < 2.
                  */
-                unsigned long hi =
-                        ((unsigned long)(skb->tail + NETIUCV_HDRLEN)) >> 31;
+                unsigned long hi = ((unsigned long)(skb_tail_pointer(skb) +
+                                    NETIUCV_HDRLEN)) >> 31;
                 int copied = 0;
                 if (hi || (skb_tailroom(skb) < 2)) {
                         nskb = alloc_skb(skb->len + NETIUCV_HDRLEN +