Java application dies from time to time with PermGen space error, but when I look at the 
memory usage it seems low from what I can tell.

It is a Tomcat application, plus there is SOLR server running (under the same tomcat).

JVM params in `catalina.sh`:

```
-Xms1024m 
-Xmx2048m 
-XX:+HeapDumpOnOutOfMemoryError 
-XX:HeapDumpPath=/path/to/logs

```

Error in `catalina.out`:

```
java.lang.OutOfMemoryError: PermGen space
Dumping heap to /path/to/logs/java_pid22335.hprof ...
Heap dump file created [107041478 bytes in 1.823 secs]
Exception in thread "pool-5-thread-1" java.lang.OutOfMemoryError: PermGen space

```

Now the first strange thing is that memory dump is only 100Mb, while heap limit is 2048Mb. When I used to have "proper" out of memory errors, dump file was close in size to the heap limit.

Second strange thing is memory usage shown by `jmap -heap 22335` seems pretty normal (when this command was run the java app was still down):

```
Attaching to process ID 22335, please wait...   
Debugger attached successfully.
Server compiler detected.
JVM version is 11.3-b02

using thread-local object allocation.
Parallel GC with 16 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 2147483648 (2048.0MB)
   NewSize          = 2686976 (2.5625MB)
   MaxNewSize       = -65536 (-0.0625MB)
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 88080384 (84.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 566689792 (540.4375MB)
   used     = 13467648 (12.84375MB)
   free     = 553222144 (527.59375MB)
   2.3765467792297907% used
From Space:
   capacity = 327680 (0.3125MB)
   used     = 0 (0.0MB)
   free     = 327680 (0.3125MB)
   0.0% used
To Space:
   capacity = 327680 (0.3125MB)
   used     = 0 (0.0MB)
   free     = 327680 (0.3125MB)
   0.0% used
PS Old Generation
   capacity = 1431699456 (1365.375MB)
   used     = 86216248 (82.22222137451172MB)
   free     = 1345483208 (1283.1527786254883MB)
   6.021951579200712% used
PS Perm Generation
   capacity = 88080384 (84.0MB)
   used     = 88080080 (83.99971008300781MB)
   free     = 304 (2.899169921875E-4MB)
   99.99965486072358% used

```

I looked at the memory dump file, nothing unusual there. Tried increasing heap limit, no difference.

Any ideas what could it be and why the dump file is so small, so is the memory usage while the app continues throwing out of memory errors?