Patch "netlink: do not enter direct reclaim from netlink_dump()" has been added to the 4.4-stable tree

Patch "netlink: do not enter direct reclaim from netlink_dump()" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    netlink: do not enter direct reclaim from netlink_dump()

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netlink-do-not-enter-direct-reclaim-from-netlink_dump.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Nov 10 16:42:45 CET 2016
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 6 Oct 2016 04:13:18 +0900
Subject: netlink: do not enter direct reclaim from netlink_dump()

From: Eric Dumazet <edumazet@google.com>


[ Upstream commit d35c99ff77ecb2eb239731b799386f3b3637a31e ]

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: 9063e21fb026 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netlink/af_netlink.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2557,7 +2557,7 @@ static int netlink_recvmsg(struct socket
 	/* 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) {
@@ -2810,14 +2810,13 @@ static int netlink_dump(struct sock *sk)
 	if (alloc_min_size < nlk->max_recvmsg_len) {
 		alloc_size = nlk->max_recvmsg_len;
 		skb = netlink_alloc_skb(sk, alloc_size, nlk->portid,
-					GFP_KERNEL |
-					__GFP_NOWARN |
-					__GFP_NORETRY);
+					(GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) |
+					__GFP_NOWARN | __GFP_NORETRY);
 	}
 	if (!skb) {
 		alloc_size = alloc_min_size;
 		skb = netlink_alloc_skb(sk, alloc_size, nlk->portid,
-					GFP_KERNEL);
+					(GFP_KERNEL & ~__GFP_DIRECT_RECLAIM));
 	}
 	if (!skb)
 		goto errout_skb;


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.4/ipv4-use-the-right-lock-for-ping_group_range.patch
queue-4.4/ipv4-disable-bh-in-set_ping_group_range.patch
queue-4.4/tcp-fix-a-compile-error-in-dbgundo.patch
queue-4.4/net-avoid-sk_forward_alloc-overflows.patch
queue-4.4/udp-fix-ip_checksum-handling.patch
queue-4.4/netlink-do-not-enter-direct-reclaim-from-netlink_dump.patch
queue-4.4/ipv6-tcp-restore-ip6cb-for-pktoptions-skbs.patch
queue-4.4/tcp-fix-overflow-in-__tcp_retransmit_skb.patch
queue-4.4/packet-on-direct_xmit-limit-tso-and-csum-to-supported-devices.patch
queue-4.4/net-pktgen-remove-rcu-locking-in-pktgen_change_name.patch