From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755502AbdBOXg0 (ORCPT ); Wed, 15 Feb 2017 18:36:26 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:54201 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753718AbdBOXgX (ORCPT ); Wed, 15 Feb 2017 18:36:23 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Greg Thelen" , "David S. Miller" , "Eric Dumazet" , "Greg Rose" , "Alexei Starovoitov" Date: Wed, 15 Feb 2017 22:41:40 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 099/306] netlink: do not enter direct reclaim from netlink_dump() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.40-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit d35c99ff77ecb2eb239731b799386f3b3637a31e upstream. 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 Reported-by: Alexei Starovoitov Cc: Greg Thelen Reviewed-by: Greg Rose Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller [bwh: Backported to 3.16: - Adjust context - Mask out __GFP_WAIT, as suggested] Signed-off-by: Ben Hutchings --- net/netlink/af_netlink.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2461,7 +2461,7 @@ static int netlink_recvmsg(struct kiocb /* 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) { @@ -2719,9 +2719,8 @@ 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_WAIT) | + __GFP_NOWARN | __GFP_NORETRY); } if (!skb) { alloc_size = alloc_min_size;