Technical Tip: Explaining the 'diagnose hardware sys slab' command

[sahmed_FTNT]

Description	This article describes how the 'diagnose hardware sys slab' command is usually used for memory troubleshooting, and elaborates on the meaning of the command's output.
Scope	FortiGate.
Solution	The memory slabs are a collection of objects used by the kernel to store information in memory. Examples of slabs: Slab Usage tcp_session TCP session ip_session Non-TCP session ip_dst_cache Route cache buffer_head Read/write data from disk, flash inode_cache Information about file and directories dentry_cache Cache for file system directory entries arp_cache Cache for ARP The command 'diagnose hardware sys slab' is often used to determine the memory status of a device during troubleshooting: In the above: active_objs        <----- Number of objects that are currently in use. num_objs              <----- Total number of allocated objects that are in use or not in use. objsize                <----- Size of objects in this slab (in bytes). objperslab        <----- Number of objects stored in each slab. pagesperslab    <----- Number of pages allocated for each slab. It is possible to calculate how much memory it is using with the following formula: (num_objs) x (objsize) = number of bytes of memory used.                       <active_objs>    <num_objs>     <objsize> tcp_session              2539            2700            1536 ip_session               3970374         3970374         1344 TCP session = 2700 (num_objs) x 1536 (objsize) = 4,147,200 bytes to Mb = 4.1Mb IP session = 3970374 (num_objs) x 1344 (objsize) =  5,336,182,656 bytes to GB = 5.33 GB The slab value can be found with the following command: get ha memory MemTotal: 2040560 kB MemFree: 937664 kB Slab: 92448 kB