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-rw-r--r--include/linux/skbuff.h2
-rw-r--r--net/core/skbuff.c28
-rw-r--r--net/ipv4/udp.c12
3 files changed, 41 insertions, 1 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9c535fbccf2c..0cd92b0f2af5 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1966,6 +1966,8 @@ static inline int pskb_may_pull(struct sk_buff *skb, unsigned int len)
return __pskb_pull_tail(skb, len - skb_headlen(skb)) != NULL;
}
+void skb_condense(struct sk_buff *skb);
+
/**
* skb_headroom - bytes at buffer head
* @skb: buffer to check
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b45cd1494243..84151cf40aeb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4931,3 +4931,31 @@ struct sk_buff *pskb_extract(struct sk_buff *skb, int off,
return clone;
}
EXPORT_SYMBOL(pskb_extract);
+
+/**
+ * skb_condense - try to get rid of fragments/frag_list if possible
+ * @skb: buffer
+ *
+ * Can be used to save memory before skb is added to a busy queue.
+ * If packet has bytes in frags and enough tail room in skb->head,
+ * pull all of them, so that we can free the frags right now and adjust
+ * truesize.
+ * Notes:
+ * We do not reallocate skb->head thus can not fail.
+ * Caller must re-evaluate skb->truesize if needed.
+ */
+void skb_condense(struct sk_buff *skb)
+{
+ if (!skb->data_len ||
+ skb->data_len > skb->end - skb->tail ||
+ skb_cloned(skb))
+ return;
+
+ /* Nice, we can free page frag(s) right now */
+ __pskb_pull_tail(skb, skb->data_len);
+
+ /* Now adjust skb->truesize, since __pskb_pull_tail() does
+ * not do this.
+ */
+ skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
+}
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 16d88ba9ff1c..f5628ada47b5 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1199,7 +1199,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
{
struct sk_buff_head *list = &sk->sk_receive_queue;
int rmem, delta, amt, err = -ENOMEM;
- int size = skb->truesize;
+ int size;
/* try to avoid the costly atomic add/sub pair when the receive
* queue is full; always allow at least a packet
@@ -1208,6 +1208,16 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
if (rmem > sk->sk_rcvbuf)
goto drop;
+ /* Under mem pressure, it might be helpful to help udp_recvmsg()
+ * having linear skbs :
+ * - Reduce memory overhead and thus increase receive queue capacity
+ * - Less cache line misses at copyout() time
+ * - Less work at consume_skb() (less alien page frag freeing)
+ */
+ if (rmem > (sk->sk_rcvbuf >> 1))
+ skb_condense(skb);
+ size = skb->truesize;
+
/* we drop only if the receive buf is full and the receive
* queue contains some other skb
*/