1 files changed, 25 insertions, 11 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 7367208ee8cd..a160b4ef5ba0 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -163,7 +163,8 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
  * adding 'size' bytes to a buffer which currently contains 'offset'
  * bytes.
  */
-static bool start_new_rx_buffer(int offset, unsigned long size, int head)
+static bool start_new_rx_buffer(int offset, unsigned long size, int head,
+                                bool full_coalesce)
 {
         /* simple case: we have completely filled the current buffer. */
         if (offset == MAX_BUFFER_OFFSET)
@@ -175,6 +176,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
          *     (i)   this frag would fit completely in the next buffer
          * and (ii)  there is already some data in the current buffer
          * and (iii) this is not the head buffer.
+         * and (iv)  there is no need to fully utilize the buffers
          *
          * Where:
          * - (i) stops us splitting a frag into two copies
@@ -185,6 +187,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
          *   by (ii) but is explicitly checked because
          *   netfront relies on the first buffer being
          *   non-empty and can crash otherwise.
+         * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
+         *   slot
          *
          * This means we will effectively linearise small
          * frags but do not needlessly split large buffers
@@ -192,7 +196,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
          * own buffers as before.
          */
         BUG_ON(size > MAX_BUFFER_OFFSET);
-        if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
+        if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head &&
+            !full_coalesce)
                 return true;
 
         return false;
@@ -227,6 +232,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
         return meta;
 }
 
+struct xenvif_rx_cb {
+        int meta_slots_used;
+        bool full_coalesce;
+};
+
+#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
+
 /*
  * Set up the grant operations for this fragment. If it's a flipping
  * interface, we also set up the unmap request from here.
@@ -261,7 +273,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
                 if (bytes > size)
                         bytes = size;
 
-                if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
+                if (start_new_rx_buffer(npo->copy_off,
+                                        bytes,
+                                        *head,
+                                        XENVIF_RX_CB(skb)->full_coalesce)) {
                         /*
                          * Netfront requires there to be some data in the head
                          * buffer.
@@ -541,12 +556,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
         }
 }
 
-struct xenvif_rx_cb {
-        int meta_slots_used;
-};
-
-#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
-
 void xenvif_kick_thread(struct xenvif *vif)
 {
         wake_up(&vif->wq);
@@ -602,10 +611,15 @@ static void xenvif_rx_action(struct xenvif *vif)
 
                 /* To avoid the estimate becoming too pessimal for some
                  * frontends that limit posted rx requests, cap the estimate
-                 * at MAX_SKB_FRAGS.
+                 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
+                 * the skb into the provided slots.
                  */
-                if (max_slots_needed > MAX_SKB_FRAGS)
+                if (max_slots_needed > MAX_SKB_FRAGS) {
                         max_slots_needed = MAX_SKB_FRAGS;
+                        XENVIF_RX_CB(skb)->full_coalesce = true;
+                } else {
+                        XENVIF_RX_CB(skb)->full_coalesce = false;
+                }
 
                 /* We may need one more slot for GSO metadata */
                 if (skb_is_gso(skb) &&