Good day,

There seem to be a large slab memory leak in standard (kernel.org)
kernel with the specific configuration and workload I have here.
From what I can tell at the moment, it appears to be a leak in
IPSec-related xfrm code.


It was really noticeable on several different physical machines
with same kernel configuration but different worloads since I've
upgraded to kernel 3.5.0.

Graph of total slab usage (+ total available RAM) on these machines:

  http://i.imgur.com/IyPqA.png

Presence of some leak can clearly be seen over time, and it caused
near-OOM condition several times now.
Sharp drops in memory usage indicates reboot, which, I'm afraid, with
such condition, has to be done at the regular intervals.

Initially I thought that it was triggered by heavy filesystem load, but
today finally got around to reboot one of the machines with
slub_debug=U and it doesn't seem to be the case.

slabtop showed "kmalloc-64" being the 99% offender in the past, but
with recent kernels (3.6.1), it has changed to "secpath_cache",
alloc_calls in /sys/kernel/slab/secpath_cache/ lists only the following:

  2779138 secpath_dup+0x1b/0x5a age=400/169538/326767 pid=0-1543 cpus=0-3

And free_calls lists these two lines:

  2543886 <not-available> age=4295223985 pid=0 cpus=0
  235252 __secpath_destroy+0x3e/0x43 age=1651/174629/327902 pid=0-1519 cpus=0-3

Contents of all paths available in /sys/kernel/slab/secpath_cache/
and "slabtop -o" output should be attached to this mail.
These were taken after heavy network + fs i/o load (rsync from a
different machine over network) after ~10-20min.

"secpath_dup" seem to be ipsec-related call, and all machines in
question communicate over IPSec almost exclusively all the time
(openswan-2.6.37 userspace at the moment).

As noted, the problem is highly reproducible - all I have to do is to
run rsync or something similar between these nodes for a few minutes.
All machines in question have x86_64 kernel 3.6.1 now, but I'll
probably update it to 3.6.2 in a moment.


Keywords:
linux kernel networking mm slub slab secpath_dup secpath_cache xfrm
ipsec 3.5 3.6 memory leak oom slabtop x86 x86_64 amd64


/proc/version: 
  Linux version 3.6.1-fg.mf_master (root@anathema) (gcc version 4.6.3
  (Exherbo gcc-4.6.3-r1) ) #1 SMP Sat Oct 13 04:21:08 YEKT 2012

Other information about the system (as per REPORTING-BUGS) is
attached, also including slabtop and slub_debug-related /sys paths
output/contents.


-- 
Mike Kazantsev // fraggod.net