sfc: Reduce size of efx_rx_buffer by unionising skb and page

[bwh: Forward-ported to net-next-2.6.]
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

2 files changed, 51 insertions, 53 deletions

diff --git a/drivers/net/sfc/net_driver.h b/drivers/net/sfc/net_driver.h
index 15b9068e5b87..59ff32ac7ec6 100644
--- a/drivers/net/sfc/net_driver.h
+++ b/drivers/net/sfc/net_driver.h
@@ -216,13 +216,17 @@ struct efx_tx_queue {
  *      If both this and skb are %NULL, the buffer slot is currently free.
  * @data: Pointer to ethernet header
  * @len: Buffer length, in bytes.
+ * @is_page: Indicates if @page is valid. If false, @skb is valid.
  */
 struct efx_rx_buffer {
         dma_addr_t dma_addr;
-        struct sk_buff *skb;
-        struct page *page;
+        union {
+                struct sk_buff *skb;
+                struct page *page;
+        } u;
         char *data;
         unsigned int len;
+        bool is_page;
 };
 
 /**
diff --git a/drivers/net/sfc/rx.c b/drivers/net/sfc/rx.c
index 3925fd621177..bcbd2ec2d92a 100644
--- a/drivers/net/sfc/rx.c
+++ b/drivers/net/sfc/rx.c
@@ -129,6 +129,7 @@ static int efx_init_rx_buffers_skb(struct efx_rx_queue *rx_queue)
         struct efx_nic *efx = rx_queue->efx;
         struct net_device *net_dev = efx->net_dev;
         struct efx_rx_buffer *rx_buf;
+        struct sk_buff *skb;
         int skb_len = efx->rx_buffer_len;
         unsigned index, count;
 
@@ -136,24 +137,24 @@ static int efx_init_rx_buffers_skb(struct efx_rx_queue *rx_queue)
                 index = rx_queue->added_count & rx_queue->ptr_mask;
                 rx_buf = efx_rx_buffer(rx_queue, index);
 
-                rx_buf->skb = netdev_alloc_skb(net_dev, skb_len);
-                if (unlikely(!rx_buf->skb))
+                rx_buf->u.skb = skb = netdev_alloc_skb(net_dev, skb_len);
+                if (unlikely(!skb))
                         return -ENOMEM;
-                rx_buf->page = NULL;
 
                 /* Adjust the SKB for padding and checksum */
-                skb_reserve(rx_buf->skb, NET_IP_ALIGN);
+                skb_reserve(skb, NET_IP_ALIGN);
+                rx_buf->data = (char *)skb->data;
                 rx_buf->len = skb_len - NET_IP_ALIGN;
-                rx_buf->data = (char *)rx_buf->skb->data;
-                rx_buf->skb->ip_summed = CHECKSUM_UNNECESSARY;
+                rx_buf->is_page = false;
+                skb->ip_summed = CHECKSUM_UNNECESSARY;
 
                 rx_buf->dma_addr = pci_map_single(efx->pci_dev,
                                                   rx_buf->data, rx_buf->len,
                                                   PCI_DMA_FROMDEVICE);
                 if (unlikely(pci_dma_mapping_error(efx->pci_dev,
                                                    rx_buf->dma_addr))) {
-                        dev_kfree_skb_any(rx_buf->skb);
-                        rx_buf->skb = NULL;
+                        dev_kfree_skb_any(skb);
+                        rx_buf->u.skb = NULL;
                         return -EIO;
                 }
 
@@ -211,10 +212,10 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
                 index = rx_queue->added_count & rx_queue->ptr_mask;
                 rx_buf = efx_rx_buffer(rx_queue, index);
                 rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
-                rx_buf->skb = NULL;
-                rx_buf->page = page;
+                rx_buf->u.page = page;
                 rx_buf->data = page_addr + EFX_PAGE_IP_ALIGN;
                 rx_buf->len = efx->rx_buffer_len - EFX_PAGE_IP_ALIGN;
+                rx_buf->is_page = true;
                 ++rx_queue->added_count;
                 ++rx_queue->alloc_page_count;
                 ++state->refcnt;
@@ -235,19 +236,17 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 static void efx_unmap_rx_buffer(struct efx_nic *efx,
                                 struct efx_rx_buffer *rx_buf)
 {
-        if (rx_buf->page) {
+        if (rx_buf->is_page && rx_buf->u.page) {
                 struct efx_rx_page_state *state;
 
-                EFX_BUG_ON_PARANOID(rx_buf->skb);
-
-                state = page_address(rx_buf->page);
+                state = page_address(rx_buf->u.page);
                 if (--state->refcnt == 0) {
                         pci_unmap_page(efx->pci_dev,
                                        state->dma_addr,
                                        efx_rx_buf_size(efx),
                                        PCI_DMA_FROMDEVICE);
                 }
-        } else if (likely(rx_buf->skb)) {
+        } else if (!rx_buf->is_page && rx_buf->u.skb) {
                 pci_unmap_single(efx->pci_dev, rx_buf->dma_addr,
                                  rx_buf->len, PCI_DMA_FROMDEVICE);
         }
@@ -256,12 +255,12 @@ static void efx_unmap_rx_buffer(struct efx_nic *efx,
 static void efx_free_rx_buffer(struct efx_nic *efx,
                                struct efx_rx_buffer *rx_buf)
 {
-        if (rx_buf->page) {
-                __free_pages(rx_buf->page, efx->rx_buffer_order);
-                rx_buf->page = NULL;
-        } else if (likely(rx_buf->skb)) {
-                dev_kfree_skb_any(rx_buf->skb);
-                rx_buf->skb = NULL;
+        if (rx_buf->is_page && rx_buf->u.page) {
+                __free_pages(rx_buf->u.page, efx->rx_buffer_order);
+                rx_buf->u.page = NULL;
+        } else if (!rx_buf->is_page && rx_buf->u.skb) {
+                dev_kfree_skb_any(rx_buf->u.skb);
+                rx_buf->u.skb = NULL;
         }
 }
 
@@ -277,7 +276,7 @@ static void efx_fini_rx_buffer(struct efx_rx_queue *rx_queue,
 static void efx_resurrect_rx_buffer(struct efx_rx_queue *rx_queue,
                                     struct efx_rx_buffer *rx_buf)
 {
-        struct efx_rx_page_state *state = page_address(rx_buf->page);
+        struct efx_rx_page_state *state = page_address(rx_buf->u.page);
         struct efx_rx_buffer *new_buf;
         unsigned fill_level, index;
 
@@ -292,16 +291,16 @@ static void efx_resurrect_rx_buffer(struct efx_rx_queue *rx_queue,
         }
 
         ++state->refcnt;
-        get_page(rx_buf->page);
+        get_page(rx_buf->u.page);
 
         index = rx_queue->added_count & rx_queue->ptr_mask;
         new_buf = efx_rx_buffer(rx_queue, index);
         new_buf->dma_addr = rx_buf->dma_addr ^ (PAGE_SIZE >> 1);
-        new_buf->skb = NULL;
-        new_buf->page = rx_buf->page;
+        new_buf->u.page = rx_buf->u.page;
         new_buf->data = (void *)
                 ((__force unsigned long)rx_buf->data ^ (PAGE_SIZE >> 1));
         new_buf->len = rx_buf->len;
+        new_buf->is_page = true;
         ++rx_queue->added_count;
 }
 
@@ -315,16 +314,15 @@ static void efx_recycle_rx_buffer(struct efx_channel *channel,
         struct efx_rx_buffer *new_buf;
         unsigned index;
 
-        if (rx_buf->page != NULL && efx->rx_buffer_len <= EFX_RX_HALF_PAGE &&
-            page_count(rx_buf->page) == 1)
+        if (rx_buf->is_page && efx->rx_buffer_len <= EFX_RX_HALF_PAGE &&
+            page_count(rx_buf->u.page) == 1)
                 efx_resurrect_rx_buffer(rx_queue, rx_buf);
 
         index = rx_queue->added_count & rx_queue->ptr_mask;
         new_buf = efx_rx_buffer(rx_queue, index);
 
         memcpy(new_buf, rx_buf, sizeof(*new_buf));
-        rx_buf->page = NULL;
-        rx_buf->skb = NULL;
+        rx_buf->u.page = NULL;
         ++rx_queue->added_count;
 }
 
@@ -428,7 +426,7 @@ static void efx_rx_packet__check_len(struct efx_rx_queue *rx_queue,
                  * data at the end of the skb will be trashed. So
                  * we have no choice but to leak the fragment.
                  */
-                *leak_packet = (rx_buf->skb != NULL);
+                *leak_packet = !rx_buf->is_page;
                 efx_schedule_reset(efx, RESET_TYPE_RX_RECOVERY);
         } else {
                 if (net_ratelimit())
@@ -454,13 +452,12 @@ static void efx_rx_packet_gro(struct efx_channel *channel,
         gro_result_t gro_result;
 
         /* Pass the skb/page into the GRO engine */
-        if (rx_buf->page) {
+        if (rx_buf->is_page) {
                 struct efx_nic *efx = channel->efx;
-                struct page *page = rx_buf->page;
+                struct page *page = rx_buf->u.page;
                 struct sk_buff *skb;
 
-                EFX_BUG_ON_PARANOID(rx_buf->skb);
-                rx_buf->page = NULL;
+                rx_buf->u.page = NULL;
 
                 skb = napi_get_frags(napi);
                 if (!skb) {
@@ -487,11 +484,10 @@ static void efx_rx_packet_gro(struct efx_channel *channel,
 
                 gro_result = napi_gro_frags(napi);
         } else {
-                struct sk_buff *skb = rx_buf->skb;
+                struct sk_buff *skb = rx_buf->u.skb;
 
-                EFX_BUG_ON_PARANOID(!skb);
                 EFX_BUG_ON_PARANOID(!checksummed);
-                rx_buf->skb = NULL;
+                rx_buf->u.skb = NULL;
 
                 gro_result = napi_gro_receive(napi, skb);
         }
@@ -514,8 +510,6 @@ void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
 
         rx_buf = efx_rx_buffer(rx_queue, index);
         EFX_BUG_ON_PARANOID(!rx_buf->data);
-        EFX_BUG_ON_PARANOID(rx_buf->skb && rx_buf->page);
-        EFX_BUG_ON_PARANOID(!(rx_buf->skb || rx_buf->page));
 
         /* This allows the refill path to post another buffer.
          * EFX_RXD_HEAD_ROOM ensures that the slot we are using
@@ -587,32 +581,32 @@ void __efx_rx_packet(struct efx_channel *channel,
                 return;
         }
 
-        if (rx_buf->skb) {
-                prefetch(skb_shinfo(rx_buf->skb));
+        if (!rx_buf->is_page) {
+                skb = rx_buf->u.skb;
+
+                prefetch(skb_shinfo(skb));
 
-                skb_reserve(rx_buf->skb, efx->type->rx_buffer_hash_size);
-                skb_put(rx_buf->skb, rx_buf->len);
+                skb_reserve(skb, efx->type->rx_buffer_hash_size);
+                skb_put(skb, rx_buf->len);
 
                 if (efx->net_dev->features & NETIF_F_RXHASH)
-                        rx_buf->skb->rxhash = efx_rx_buf_hash(rx_buf);
+                        skb->rxhash = efx_rx_buf_hash(rx_buf);
 
                 /* Move past the ethernet header. rx_buf->data still points
                  * at the ethernet header */
-                rx_buf->skb->protocol = eth_type_trans(rx_buf->skb,
-                                                       efx->net_dev);
+                skb->protocol = eth_type_trans(skb, efx->net_dev);
 
-                skb_record_rx_queue(rx_buf->skb, channel->channel);
+                skb_record_rx_queue(skb, channel->channel);
         }
 
-        if (likely(checksummed || rx_buf->page)) {
+        if (likely(checksummed || rx_buf->is_page)) {
                 efx_rx_packet_gro(channel, rx_buf, checksummed);
                 return;
         }
 
         /* We now own the SKB */
-        skb = rx_buf->skb;
-        rx_buf->skb = NULL;
-        EFX_BUG_ON_PARANOID(!skb);
+        skb = rx_buf->u.skb;
+        rx_buf->u.skb = NULL;
 
         /* Set the SKB flags */
         skb_checksum_none_assert(skb);