NMT does not seem to count malloc correctly

[Thomas Stüfe]

Hi,

maybe I am missing something fundamental, or there is something wrong with
NMT.

As an experiment for an unrelated issue, I created a C-Heap leak by simply
commenting out the ::free() call inside os::free():

--- a/src/hotspot/share/runtime/os.cpp  Thu Aug 06 17:08:02 2020 +0200
+++ b/src/hotspot/share/runtime/os.cpp  Thu Aug 06 17:08:08 2020 +0200
@@ -804,7 +804,7 @@
   size_t size = guarded.get_user_size();
   inc_stat_counter(&free_bytes, size);
   membase = guarded.release_for_freeing();
-  ::free(membase);
+//  ::free(membase);
 #else
   void* membase = MemTracker::record_free(memblock,
MemTracker::tracking_level());
   ::free(membase);

As expected, this leads quickly to a very high memory usage. In my tiny
example (which really does not matter) I quickly end up with ~4G RSS, and
the glibc reports about 3G outstanding allocations:

Process Memory:
Virtual Size: 11136852K (peak: 11136852K)
Resident Set Size: 4057860K (peak: 4057860K) (anon: 4013076K, file: 44784K,
shmem: 0K)
Swapped out: 0K
C-Heap outstanding allocations: 3070399K


However, NMT reports just about 600M committed memory (into this number
should fall all outstanding allocations done with os::malloc() AFAICS):

thomas at mainframe:~$ jjjcmd Interl VM.native_memory   scale=1

19441:

Native Memory Tracking:

Total: reserved=6227876720, committed=626285424

....

And the malloc information adds up to about only 68M:

thomas at mainframe:~$ jjjcmd Interl VM.native_memory   scale=1  | grep malloc
                            (malloc=4044913 #55107)
                            (malloc=38688 #146)
                            (malloc=10812522 #258557)
                            (malloc=18157899 #3629)
                            (malloc=42496 #311)
                            (malloc=216 #7)
                            (malloc=594920 #1788)
                            (malloc=27304 #2)
                            (malloc=2781872 #60716)
                            (malloc=543008 #5144)
                            (malloc=200416)
                            (malloc=152 #7)
                            (malloc=6788 #214)
                            (malloc=18977 #485)
                            (malloc=994280 #2797)
                            (malloc=153248 #744)
                            (malloc=2152 #12)

I must be missing something obvious here. What is it?

Thank you,

Thomas