bug: Strings in luajit are infinitely bloated, even if they are not rereferenced in the lua vm

[fairyqb]

Strings in luajit are infinitely bloated, even if they are not rereferenced in the lua vm. As a result, the memory resources of the nginx process RES are increasing to become larger and larger.

Minimal example code

resty example.lua

`
local function get_memory_usage()
local b = collectgarbage("count") * 1024
return b
end

local my_table = {}  
for i = 1, 10000000 do  
    my_table[i] =  string.rep("A" , 256) .. i  

end

my_table = nil
print("start gc:", "mem:",get_memory_usage())
collectgarbage("collect") 
print("end gc:", "mem:",get_memory_usage())
print("sleep 10m")

print("done")
ngx.sleep(60*10*6)

`