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Commit eb6a2481 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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af_unix: reduce high order page allocations 



unix_dgram_sendmsg() currently builds linear skbs, and this can stress
page allocator with high order page allocations. When memory gets
fragmented, this can eventually fail.

We can try to use order-2 allocations for skb head (SKB_MAX_ALLOC) plus
up to 16 page fragments to lower pressure on buddy allocator.

This patch has no effect on messages of less than 16064 bytes.
(on 64bit arches with PAGE_SIZE=4096)

For bigger messages (from 16065 to 81600 bytes), this patch brings
reliability at the expense of performance penalty because of extra pages
allocations.

netperf -t DG_STREAM -T 0,2 -- -m 16064 -s 200000
->4086040 Messages / 10s

netperf -t DG_STREAM -T 0,2 -- -m 16068 -s 200000
->3901747 Messages / 10s

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent edbc0bb3

net/unix/af_unix.c

+12 −3
Original line number Diff line number Diff line
@@ -1442,6 +1442,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock, 
	long timeo;

	struct scm_cookie tmp_scm;

	int max_level;

	int data_len = 0;



	if (NULL == siocb->scm)

		siocb->scm = &tmp_scm;
@@ -1475,7 +1476,13 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock, 
	if (len > sk->sk_sndbuf - 32)

		goto out;



	skb = sock_alloc_send_skb(sk, len, msg->msg_flags&MSG_DONTWAIT, &err);

	if (len > SKB_MAX_ALLOC)

		data_len = min_t(size_t,

				 len - SKB_MAX_ALLOC,

				 MAX_SKB_FRAGS * PAGE_SIZE);



	skb = sock_alloc_send_pskb(sk, len - data_len, data_len,

				   msg->msg_flags & MSG_DONTWAIT, &err);

	if (skb == NULL)

		goto out;
@@ -1485,8 +1492,10 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock, 
	max_level = err + 1;

	unix_get_secdata(siocb->scm, skb);



	skb_reset_transport_header(skb);

	err = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);

	skb_put(skb, len - data_len);

	skb->data_len = data_len;

	skb->len = len;

	err = skb_copy_datagram_from_iovec(skb, 0, msg->msg_iov, 0, len);

	if (err)

		goto out_free;