From 9063e21fb026c4966fc93261c18322214f9835eb Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 7 Mar 2014 12:02:33 -0800 Subject: [PATCH] netlink: autosize skb lengthes One known problem with netlink is the fact that NLMSG_GOODSIZE is really small on PAGE_SIZE==4096 architectures, and it is difficult to know in advance what buffer size is used by the application. This patch adds an automatic learning of the size. First netlink message will still be limited to ~4K, but if user used bigger buffers, then following messages will be able to use up to 16KB. This speedups dump() operations by a large factor and should be safe for legacy applications. Signed-off-by: Eric Dumazet Cc: Thomas Graf Acked-by: Thomas Graf Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 27 ++++++++++++++++++++++++++- net/netlink/af_netlink.h | 1 + 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 9db8bab27fa2..c2d585c4f7c5 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2343,6 +2343,11 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, } #endif + /* Record the max length of recvmsg() calls for future allocations */ + nlk->max_recvmsg_len = max(nlk->max_recvmsg_len, len); + nlk->max_recvmsg_len = min_t(size_t, nlk->max_recvmsg_len, + 16384); + copied = data_skb->len; if (len < copied) { msg->msg_flags |= MSG_TRUNC; @@ -2587,7 +2592,27 @@ static int netlink_dump(struct sock *sk) if (!netlink_rx_is_mmaped(sk) && atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) goto errout_skb; - skb = netlink_alloc_skb(sk, alloc_size, nlk->portid, GFP_KERNEL); + + /* NLMSG_GOODSIZE is small to avoid high order allocations being + * required, but it makes sense to _attempt_ a 16K bytes allocation + * to reduce number of system calls on dump operations, if user + * ever provided a big enough buffer. + */ + if (alloc_size < nlk->max_recvmsg_len) { + skb = netlink_alloc_skb(sk, + nlk->max_recvmsg_len, + nlk->portid, + GFP_KERNEL | + __GFP_NOWARN | + __GFP_NORETRY); + /* available room should be exact amount to avoid MSG_TRUNC */ + if (skb) + skb_reserve(skb, skb_tailroom(skb) - + nlk->max_recvmsg_len); + } + if (!skb) + skb = netlink_alloc_skb(sk, alloc_size, nlk->portid, + GFP_KERNEL); if (!skb) goto errout_skb; netlink_skb_set_owner_r(skb, sk); diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h index acbd774eeb7c..ed13a790b00e 100644 --- a/net/netlink/af_netlink.h +++ b/net/netlink/af_netlink.h @@ -31,6 +31,7 @@ struct netlink_sock { u32 ngroups; unsigned long *groups; unsigned long state; + size_t max_recvmsg_len; wait_queue_head_t wait; bool cb_running; struct netlink_callback cb; -- 2.20.1