Re: Still OOM problems with 4.9er kernels

From: Gerhard Wiesinger
Date: Fri Dec 09 2016 - 13:02:33 EST

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
cp /proc/vmstat vmstat.$(date +%s)
sleep 1s

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):



// 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;

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");

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

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

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

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

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

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

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


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


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


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

return 0;