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[Brian Murray <brian@xxxxxxxxxx>]

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https://bugs.launchpad.net/bugs/1513673

Title:
  15.10 swapping heavily after process exceeds 50% physical RAM

Status in linux package in Ubuntu:
  New

Bug description:
  I am experiencing a memory management problem with 15.10 that I did
  not experience with 15.04.  I have a 24-core (48 thread) server with
  64G of RAM.  I am getting some strange behavior with respect to
  swapping and physical memory use.

  You can see my problem in 'top':

  top - 18:52:09 up 1 day, 2:25, 3 users, load average: 1.64, 1.30, 1.18
  Tasks: 525 total, 2 running, 523 sleeping, 0 stopped, 0 zombie
  %Cpu(s): 0.3 us, 1.3 sy, 0.0 ni, 97.0 id, 1.4 wa, 0.0 hi, 0.0 si, 0.0 st
  KiB Mem: 65937528 total, 37526160 used, 28411368 free, 14396 buffers
  KiB Swap: 67071996 total, 67071724 used, 272 free. 104304 cached Mem

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 
  363 root 20 0 0 0 0 R 100.0 0.0 324:02.98 kswapd0 
  6725 theosib 20 0 99.398g 0.034t 8920 D 12.0 55.1 59:08.71 common_shell_ex 

  There's a single user logged in (me), and I have a single process
  using a large amount of virtual memory. However, something is limiting
  it to around half the physical memory, while the swap partition is
  basically full. I've watched these processes (Synopsys Design
  Compiler) run, and they don't break the 50% mark until swap fills. And
  another weird thing is that kswapd0 uses very high (usually 100%) CPU.
  AFAIK, kswapd0 should be I/O bound and therefore not use a lot of CPU
  time.

  I've looked to see if there were any limits being imposed, but ulimit
  says otherwise:

  $ ulimit -a
  core file size (blocks, -c) 0
  data seg size (kbytes, -d) unlimited
  scheduling priority (-e) 0
  file size (blocks, -f) unlimited
  pending signals (-i) 257447
  max locked memory (kbytes, -l) 64
  max memory size (kbytes, -m) unlimited
  open files (-n) 1024
  pipe size (512 bytes, -p) 8
  POSIX message queues (bytes, -q) 819200
  real-time priority (-r) 0
  stack size (kbytes, -s) 8192
  cpu time (seconds, -t) unlimited
  max user processes (-u) 257447
  virtual memory (kbytes, -v) unlimited
  file locks (-x) unlimited

  I've also tried setting swappiness to 10, but that didn't help.

  This is a pretty serious problem.  What used to take a few hours on
  15.04 now takes more than 5 to 10 times longer, because the process is
  forced to wait on swap, which is reading and writing at about 20M/sec
  each.  So it's hammering my SSD that contains the swap partition and
  going really slow.

  I've done some googling about kswapd0 using high CPU, and all I can
  work out is that some people think it's a kernel bug.

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