This KB describes how Heap Util peaks at almost 100% under massive VLAN and ESI-LAG conditions.

set forwarding-options lag-heap-optimization ( Need to reboot to apply the feature) 

## enabled 48ports w/ 4K vlan

{master:0}[edit]

jun@test# run show chassis fpc 

Jul 17 11:04:08

                     Temp  CPU Utilization (%)   CPU Utilization (%)  Memory    Utilization (%)

Slot State            (C)  Total  Interrupt      1min   5min   15min  DRAM (MB) Heap     Buffer

  0  Online            33      4          0       21     17     10    16384      76         49       

--- Customer reported that Heap Util peaks at almost 100%
--- The issue occurred with the following condition
       vlan number per AE port: 3992
       physical interface: 48
       AE interface as ESI: 48 
       1 MAC-VRF

jun@TEST> request pfe execute command "show l2 manager statistics mem_allocations" target fpc0    
SENT: Ukern command: show l2 manager statistics mem_allocations

  Memory      Allocated   Freed     Allocated
              (total)               (current)
---------------------------------------------
 IFD          114       0         114
 IFL          100       0         100
 IFF          0         0         0
 IFBD         1383696   234000    1149696
 BD           11977     0         11977
 IFL_IFBD     461236    78000     383236
 RTB          12        0         12
--- snip ---
 VNID         3992      0         3992

jun@TEST> show chassis fpc 
                     Temp  CPU Utilization (%)   CPU Utilization (%)  Memory    Utilization (%)
Slot State            (C)  Total  Interrupt      1min   5min   15min  DRAM (MB) Heap     Buffer
  0  Online            33      3          0        5      7      6    16384      98         49                               <<<<<

This behavior is a product limitation. The limitation is enhanced at junos:23.4R2-S6 & 25.4R1 later