Slab Unreclaimable is continually growing

[Matthias Böttcher <matthias.boettcher@gmail.com>]

Hi list,

my buster is using more and more memory until the oom-killer is
invoked. This occurs after two days of uptime, but no process is using
that memory. Slab seems suspicious to me.

Kernel: 4.19.37-5+deb10u1 (2019-07-19) x86_64

from /proc/meminfo after 8 hours uptime:

MemTotal:        4041116 kB
MemFree:         3165992 kB
MemAvailable:    3246560 kB
Buffers:           30144 kB
Cached:           240356 kB
SwapCached:            0 kB
Active:           162056 kB
Inactive:         144268 kB
SwapTotal:       4194300 kB
SwapFree:        4194300 kB

Slab:             521364 kB
SReclaimable:      66776 kB
SUnreclaim:       454588 kB

My Top 5 in slabtop:

$ sudo slabtop --sort c --once | head -n12

 Active / Total Objects (% used)    : 2234301 / 2270100 (98,4%)
 Active / Total Slabs (% used)      : 70832 / 70832 (100,0%)
 Active / Total Caches (% used)     : 98 / 124 (79,0%)
 Active / Total Size (% used)       : 501034,52K / 509459,17K (98,3%)
 Minimum / Average / Maximum Object : 0,01K / 0,22K / 8,00K

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
307534 304741  99%    0,20K  16186       19     64744K vm_area_struct
 14280  14274  99%    3,69K   1785        8     57120K task_struct
178048 152224  85%    0,25K  11128       16     44512K filp
  8536   8536 100%    4,00K   1067        8     34144K kmalloc-4096
 14640  14640 100%    2,06K    976       15     31232K sighand_cache

Active / Total Size is growing continually about 60 MB per hour.

How can I detect what is eating up my memory in SUnreclaim (slab unreclaimable)?

Thanks in advance
Matthias Böttcher