What is the correct header size for L2ARC in RAM?

[myuki]

I have searched online and looked up documents. There's no definitive statement regarding header size for L2ARC in RAM. I found the following possible answers:

• 96 bytes, says TrueNAS (iXsystems)
• 80 bytes, says Klara
• 70 bytes, also says Klara

Could anyone provide me with the exact answer? Perhaps a reference to the source code would be helpful.

[amotin]

OpenZFS master on FreeBSD as of today:

# vmstat -z | egrep 'l2|SIZE'
ITEM                   SIZE   LIMIT     USED     FREE      REQ FAIL SLEEP XDOM
arc_buf_hdr_t_l2only:    96,      0,       0,       0,       0,   0,   0,   0

[myuki]

Thanks for answer. Is there a way to check that on Linux (or more specific TrueNAS)?

[amotin]

# egrep 'objsize|l2' /proc/spl/kmem/slab 
name                                    flags      size     alloc slabsize  objsize  total alloc   max  total alloc   max  dlock alloc   max
arc_buf_hdr_t_l2only                  0x00100         -         0        -       96      -     -     -      -     0     -      -     -     -