[PATCH net-next] tcp: reduce memory needs of out of order queue
From: Eric Dumazet <hidden>
Date: 2011-10-14 07:19:57
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
Many drivers allocates big skb to store a single TCP frame. (WIFI drivers, or NIC using PAGE_SIZE fragments) Its now common to get skb->truesize bigger than 4096 to store a ~1500 bytes TCP frame. TCP sessions with large RTT and packet losses can fill their Out Of Order queue with such oversized skbs, and hit their sk_rcvbuf limit, starting a pruning of complete OFO queue, without giving chance to receive the missing packet(s) and moving skbs from OFO to receive queue. This patch adds skb_reduce_truesize() helper, and uses it for all skbs queued into OFO queue. Spending some time to perform a copy is worth the pain, since it permits SACK processing to have a chance to complete over the RTT barrier. This greatly improves user experience, without added cost on fast path. Signed-off-by: Eric Dumazet <redacted> --- net/ipv4/tcp_input.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c1653fe..1d10edb 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c@@ -4426,6 +4426,25 @@ static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size) return 0; } +/* + * Caller want to reduce memory needs before queueing skb + * The (expensive) copy should not be be done in fast path. + */ +static struct sk_buff *skb_reduce_truesize(struct sk_buff *skb) +{ + if (skb->truesize > 2 * SKB_TRUESIZE(skb->len)) { + struct sk_buff *nskb; + + nskb = skb_copy_expand(skb, skb_headroom(skb), 0, + GFP_ATOMIC | __GFP_NOWARN); + if (nskb) { + __kfree_skb(skb); + skb = nskb; + } + } + return skb; +} + static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) { struct tcphdr *th = tcp_hdr(skb);
@@ -4553,6 +4572,11 @@ drop: SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); + /* Since this skb might stay on ofo a long time, try to reduce + * its truesize (if its too big) to avoid future pruning. + * Many drivers allocate large buffers even to hold tiny frames. + */ + skb = skb_reduce_truesize(skb); skb_set_owner_r(skb, sk); if (!skb_peek(&tp->out_of_order_queue)) {