From a0229dae4d7a1c326fa837dcaa4b088455faead7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 15 May 2015 12:39:28 -0700 Subject: [PATCH] tcp: fix behavior for epoll edge trigger Under memory pressure, tcp_sendmsg() can fail to queue a packet while no packet is present in write queue. If we return -EAGAIN with no packet in write queue, no ACK packet will ever come to raise EPOLLOUT. We need to allow one skb per TCP socket, and make sure that tcp sockets can release their forward allocations under pressure. This is a followup to commit 3aa70b301daf ("tcp: set SOCK_NOSPACE under memory pressure") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index ecccfdc50d76d..9eabfd3e09256 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -815,9 +815,20 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp) /* The TCP header must be at least 32-bit aligned. */ size = ALIGN(size, 4); + if (unlikely(tcp_under_memory_pressure(sk))) + sk_mem_reclaim_partial(sk); + skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp); - if (skb) { - if (sk_wmem_schedule(sk, skb->truesize)) { + if (likely(skb)) { + bool mem_schedule; + + if (skb_queue_len(&sk->sk_write_queue) == 0) { + mem_schedule = true; + sk_forced_mem_schedule(sk, skb->truesize); + } else { + mem_schedule = sk_wmem_schedule(sk, skb->truesize); + } + if (likely(mem_schedule)) { skb_reserve(skb, sk->sk_prot->max_header); /* * Make sure that we have exactly size bytes -- 2.39.5