Commit d35c99ff authored Oct 06, 2016 by Eric Dumazet Committed by David S. Miller Oct 06, 2016

netlink: do not enter direct reclaim from netlink_dump()



Since linux-3.15, netlink_dump() can use up to 16384 bytes skb
allocations.

Due to struct skb_shared_info ~320 bytes overhead, we end up using
order-3 (on x86) page allocations, that might trigger direct reclaim and
add stress.

The intent was really to attempt a large allocation but immediately
fallback to a smaller one (order-1 on x86) in case of memory stress.

On recent kernels (linux-4.4), we can remove __GFP_DIRECT_RECLAIM to
meet the goal. Old kernels would need to remove __GFP_WAIT

While we are at it, since we do an order-3 allocation, allow to use
all the allocated bytes instead of 16384 to reduce syscalls during
large dumps.

iproute2 already uses 32KB recvmsg() buffer sizes.

Alexei provided an initial patch downsizing to SKB_WITH_OVERHEAD(16384)

Fixes: 9063e21f ("netlink: autosize skb lengthes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Alexei Starovoitov <ast@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Reviewed-by: Greg Rose <grose@lightfleet.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 66644982

net/netlink/af_netlink.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -1832,7 +1832,7 @@ static int netlink_recvmsg(struct socket sock, struct msghdr msg, size_t len,
		/* 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);
		SKB_WITH_OVERHEAD(32768));

		copied = data_skb->len;
		if (len < copied) {
		@@ -2083,7 +2083,8 @@ static int netlink_dump(struct sock *sk)

		if (alloc_min_size < nlk->max_recvmsg_len) {
		alloc_size = nlk->max_recvmsg_len;
		skb = alloc_skb(alloc_size, GFP_KERNEL \|
		skb = alloc_skb(alloc_size,
		(GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) \|
		__GFP_NOWARN \| __GFP_NORETRY);
		}
		if (!skb) {

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