From 8e4d980ac21596a9b91d8e720c77ad081975a0a8 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 790ba4566c1a ("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 ecccfdc50d76..9eabfd3e0925 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 -- 2.30.2