Re: Still OOM problems with 4.9er kernels

[Gerhard Wiesinger]

On 09.12.2016 18:30, Michal Hocko wrote:
> On Fri 09-12-16 17:58:14, Gerhard Wiesinger wrote:
> > On 09.12.2016 17:09, Michal Hocko wrote:
> [...]
> > > > [97883.882611] Mem-Info:
> > > > [97883.883747] active_anon:2915 inactive_anon:3376 isolated_anon:0
> > > >                   active_file:3902 inactive_file:3639 isolated_file:0
> > > >                   unevictable:0 dirty:205 writeback:0 unstable:0
> > > >                   slab_reclaimable:9856 slab_unreclaimable:9682
> > > >                   mapped:3722 shmem:59 pagetables:2080 bounce:0
> > > >                   free:748 free_pcp:15 free_cma:0
> > > there is still some page cache which doesn't seem to be neither dirty
> > > nor under writeback. So it should be theoretically reclaimable but for
> > > some reason we cannot seem to reclaim that memory.
> > > There is still some anonymous memory and free swap so we could reclaim
> > > it as well but it all seems pretty down and the memory pressure is
> > > really large
> > Yes, it might be large on the update situation, but that should be handled
> > by a virtual memory system by the kernel, right?
> Well this is what we try and call it memory reclaim. But if we are not
> able to reclaim anything then we eventually have to give up and trigger
> the OOM killer.

I'm not familiar with the Linux implementation of the VM system in 
detail. But can't you reserve as much memory for the kernel (non 
pageable) at least that you can swap everything out (even without 
killing a process at least as long there is enough swap available, which 
should be in all of my cases)?


>   Now the information that 4.4 made a difference is
> interesting. I do not really see any major differences in the reclaim
> between 4.3 and 4.4 kernels. The reason might be somewhere else as well.
> E.g. some of the subsystem consumes much more memory than before.
>
> Just curious, what kind of filesystem are you using?

I'm using ext4 only with virt-* drivers (storage, network). But it is 
definitly a virtual memory allocation/swap usage issue.

>   Could you try some
> additional debugging. Enabling reclaim related tracepoints might tell us
> more. The following should tell us more
> mount -t tracefs none /trace
> echo 1 > /trace/events/vmscan/enable
> echo 1 > /trace/events/writeback/writeback_congestion_wait/enable
> cat /trace/trace_pipe > trace.log
>
> Collecting /proc/vmstat over time might be helpful as well
> mkdir logs
> while true
> do
> 	cp /proc/vmstat vmstat.$(date +%s)
> 	sleep 1s
> done

Activated it. But I think it should be very easy to trigger also on your 
side. A very small configured VM with a program running RAM 
allocations/writes (I guess you have some testing programs already) 
should be sufficient to trigger it. You can also use the attached 
program which I used to trigger such situations some years ago. If it 
doesn't help try to reduce the available CPU for the VM and also I/O 
(e.g. use all CPU/IO on the host or other VMs).

BTW: Don't know if you have seen also my original message on the kernel 
mailinglist only:

Linus had also OOM problems with 1kB RAM requests and a lot of free RAM 
(use a translation service for the german page):
https://lkml.org/lkml/2016/11/30/64
https://marius.bloggt-in-braunschweig.de/2016/11/17/linuxkernel-4-74-8-und-der-oom-killer/
https://www.spinics.net/lists/linux-mm/msg113661.html

Thnx.

Ciao,
Gerhard

// mallocsleep.c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

typedef unsigned int BOOL;
typedef char* PCHAR;
typedef unsigned int DWORD;
typedef unsigned long DDWORD;

#define FALSE 0
#define TRUE 1

BOOL getlong(PCHAR s, DDWORD* retvalue)
{
  char *eptr;
  long value;

  value=strtoll(s,&eptr,0);
  if ((eptr == s)||(*eptr != '\0')) return FALSE;
  if (value < 0) return FALSE;
  *retvalue = value;
  return TRUE;
}

int main(int argc, char* argv[])
{
  unsigned long* p;
  unsigned long size = 16*1024*1024;
  unsigned long size_of = sizeof(*p);
  unsigned long i;
  unsigned long sleep_allocated = 3600;
  unsigned long sleep_freed = 3600;

  if (argc > 1)
  {
    if (!getlong(argv[1], &size))
    {
      printf("Wrong memsize!\n");
      exit(1);
    }
  }

  if (argc > 2)
  {
    if (!getlong(argv[2], &sleep_allocated))
    {
      printf("Wrong sleep_allocated time!\n");
      exit(1);
    }
  }

  if (argc > 3)
  {
    if (!getlong(argv[3], &sleep_freed))
    {
      printf("Wrong sleep_freed time!\n");
      exit(1);
    }
  }

  printf("size=%lu, size_of=%lu\n", size, size_of);
  fflush(stdout);

  p = malloc(size);
  if (!p)
  {
    printf("Could not allocate memory!\n");
    exit(2);
  }

  printf("malloc done, writing to memory, p=%p ...\n", (void*)p);
  fflush(stdout);

  for(i = 0;i < (size/size_of);i++) p[i]=i;

  printf("writing to memory done, sleeping for %lu seconds ...\n", 
sleep_allocated);
  fflush(stdout);

  sleep(sleep_allocated);

  printf("sleeping done, freeing ...\n");
  fflush(stdout);

  free(p);

  printf("freeing done, sleeping for %lu seconds ...\n", sleep_freed);
  fflush(stdout);

  sleep(sleep_freed);

  printf("sleeping done, exitiing ...\n");
  fflush(stdout);

  exit(0);
  return 0;
}