How to monitore Free heap size

[Gytis]

I have a problem on my internet router SR-7102 and it happens second time in a few months period. It appears like internet browsing occasionally stops.
Event log shows many events like:
[notice] FIREWALL: id=firewall ... msg="Maximum number of global associations reached, dropping packet ....
Just a few minutes before first message above I found root cause to those messages:
msg="Available heap free does not allow for a new association, dropping packet ......
Searching documentation and forums gave me nothing. Was trying 'clear' command for buffers, ip cache, ip policy-sessions- none helped. Router reload was the only resolution of the problem. Anybody has idea how to avoid this in the future?

The caommand "show memory heap"
schows:
Memory Heap:
HeapFree: 838640
HeapSize: 61508592

Block Managers:
Mgr Size Used Free Max-Used
0 0 0 2 2
1 32 630521 85 630606
2 96 9028 1967 10995
3 224 733 18 751
4 480 909 1934 2843
5 992 84 7 91
6 2016 53 44 97
7 4064 29 18 47
8 8160 37 2 39
9 16352 37 15 52
10 32736 6 4 10
11 65504 6 2 8
12 131040 6 0 6
13 262112 1 0 1
14 524256 0 0 0
15 1048544 0 0 0
16 2097120 0 0 0
17 4194272 0 0 0
18 8388576 0 0 0
19 16777184 0 0 0

Is there some OID for monitoring of free HeapFree size?
Or maybe good data base of OID's where I can find this and many others OID's for HP devices, especialy routers?