locality of extent status tree traversal

[Probir Roy]

Hi,

I am running Phoronix-fio benchmark on Linux kernel 4.18.0-rc5. I
observe the same nodes have been traversed on the extent status tree
in "ext4_es_lookup_extent" function when ext4 write begins. What's the
locality signature of ext4_es_lookup_extent? Is it possible that same
logical block being looked up repeatedly (Temporal)? Is it possible
that co-located logical blocks are searched by ext4_es_lookup_extent
(spatial)?

-- 
Probir Roy