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Known issue #915585 impacts FortiGate virtual machine appliances running FortiOS v7.2.4 to v7.2.7 or v7.4.0 to v7.4.1.
After upgrading the FortiGate VM to either of these firmware versions, the SLAB memory increases constantly. Which results in the FortiGate VM entering the memory conserve mode.
To verify the slab memory usage, use the below commands:
diagnose hardware sysinfo memory
MemTotal: 8170028 kB
MemFree: 228672 kB
**output-omitted**
Slab: 4766984 kB <------------ This is the SLAB memory usage.
SReclaimable: 354420 kB
SUnreclaim: 4412564 kB
**output-omitted**
diagnose sys session full-stat
session table: table_size=2097152 max_depth=2 used=2971
misc info: session_count=1003 setup_rate=0 exp_count=0 clash=109
**output-omitted**
diagnose hardware sysinfo slab
#name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
**output-omitted**
tcp_session 1997395 1997400 1600 5 2 : tunables 24 12 8 : slabdata 399480 399480 0
ip_session 125397 125400 1408 5 2 : tunables 24 12 8 : slabdata 25080 25080 0
**output-omitted**
The above output shows an unusually high total count of slab objects for the TCP and non-TCP sessions, despite the session count being relatively low.
The session count and the total ‘<num_objs>’ for tcp_session and ip_session should be relatively close. The problem occurs when the slab objects fail to deallocate the memory once the session ends, which results in a disproportionately high number of slab objects relative to the actual number of sessions.
This issue is fixed in FortiOS v7.2.8 and FortiOS 7.4.2, upgrading the FortiGate virtual machine appliance to either of these firmware versions will resolve this issue.
Note: This issue only affects the FortiGate virtual machine appliances and not the hardware FortiGate models.
Related documents:
Resolved issues 7.2.8
Resolved issues 7.4.2
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