From 9aee41eff751e4c789ff785c561d7bf7ad72c286 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 13 Sep 2018 07:58:41 -0700 Subject: inet: frags: use rhashtables for reassembly units Some applications still rely on IP fragmentation, and to be fair linux reassembly unit is not working under any serious load. It uses static hash tables of 1024 buckets, and up to 128 items per bucket (!!!) A work queue is supposed to garbage collect items when host is under memory pressure, and doing a hash rebuild, changing seed used in hash computations. This work queue blocks softirqs for up to 25 ms when doing a hash rebuild, occurring every 5 seconds if host is under fire. Then there is the problem of sharing this hash table for all netns. It is time to switch to rhashtables, and allocate one of them per netns to speedup netns dismantle, since this is a critical metric these days. Lookup is now using RCU. A followup patch will even remove the refcount hold/release left from prior implementation and save a couple of atomic operations. Before this patch, 16 cpus (16 RX queue NIC) could not handle more than 1 Mpps frags DDOS. After the patch, I reach 9 Mpps without any tuning, and can use up to 2GB of storage for the fragments (exact number depends on frags being evicted after timeout) $ grep FRAG /proc/net/sockstat FRAG: inuse 1966916 memory 2140004608 A followup patch will change the limits for 64bit arches. Signed-off-by: Eric Dumazet Cc: Kirill Tkhai Cc: Herbert Xu Cc: Florian Westphal Cc: Jesper Dangaard Brouer Cc: Alexander Aring Cc: Stefan Schmidt Signed-off-by: David S. Miller (cherry picked from commit 648700f76b03b7e8149d13cc2bdb3355035258a9) Signed-off-by: Greg Kroah-Hartman --- Documentation/networking/ip-sysctl.txt | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) (limited to 'Documentation/networking') diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index d499676890d8..f23582a3c661 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -134,13 +134,10 @@ min_adv_mss - INTEGER IP Fragmentation: ipfrag_high_thresh - INTEGER - Maximum memory used to reassemble IP fragments. When - ipfrag_high_thresh bytes of memory is allocated for this purpose, - the fragment handler will toss packets until ipfrag_low_thresh - is reached. This also serves as a maximum limit to namespaces - different from the initial one. + Maximum memory used to reassemble IP fragments. ipfrag_low_thresh - INTEGER + (Obsolete since linux-4.17) Maximum memory used to reassemble IP fragments before the kernel begins to remove incomplete fragment queues to free up resources. The kernel still accepts new fragments for defragmentation. -- cgit v1.2.3