From c8628155ece363487b57d33441ea0359018c0fa7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 18 Mar 2012 11:07:47 +0000 Subject: tcp: reduce out_of_order memory use MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit With increasing receive window sizes, but speed of light not improved that much, out of order queue can contain a huge number of skbs, waiting to be moved to receive_queue when missing packets can fill the holes. Some devices happen to use fat skbs (truesize of 4096 + sizeof(struct sk_buff)) to store regular (MTU <= 1500) frames. This makes highly probable sk_rmem_alloc hits sk_rcvbuf limit, which can be 4Mbytes in many cases. When limit is hit, tcp stack calls tcp_collapse_ofo_queue(), a true latency killer and cpu cache blower. Doing the coalescing attempt each time we add a frame in ofo queue permits to keep memory use tight and in many cases avoid the tcp_collapse() thing later. Tested on various wireless setups (b43, ath9k, ...) known to use big skb truesize, this patch removed the "packets collapsed in receive queue due to low socket buffer" I had before. This also reduced average memory used by tcp sockets. With help from Neal Cardwell. Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Cc: H.K. Jerry Chu Cc: Tom Herbert Cc: Ilpo Järvinen Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- include/linux/snmp.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/snmp.h') diff --git a/include/linux/snmp.h b/include/linux/snmp.h index 8ee8af4e6da9..2e68f5ba0389 100644 --- a/include/linux/snmp.h +++ b/include/linux/snmp.h @@ -233,6 +233,7 @@ enum LINUX_MIB_TCPREQQFULLDOCOOKIES, /* TCPReqQFullDoCookies */ LINUX_MIB_TCPREQQFULLDROP, /* TCPReqQFullDrop */ LINUX_MIB_TCPRETRANSFAIL, /* TCPRetransFail */ + LINUX_MIB_TCPRCVCOALESCE, /* TCPRcvCoalesce */ __LINUX_MIB_MAX }; -- cgit v1.2.3