ruby - Why the large difference between stack memory limit systems? -

i wrote implementation of algorithm course ruby 2.1 running in ubuntu. algorithm easiest express utilising recursion. ruby raising "stack level deep systemstack" exception due large memory requirements of problem , implementation. allow algorithm complete used following commands increase allowable stack size:

export ruby_thread_vm_stack_size=16000000  ulimit -s 128000 

note both commands above have run. units of ruby_thread_vm_stack_size bytes , units of ulimit kbytes. ruby_thread_vm_stack_size limit ~16mbytes , ulimit limit ~128mbytes. if reduce either limit half it's value shown here algorithm won't finish without exception.

can please explain why these limits differ factor of ~8?

i've checked i'm able , doesn't seem because 1 of units kbits instead of kbytes. thanks!

i believe ulimit needs bigger due ruby's boilerplate around function calls.

in /vm_eval.c see this:

• rb_call0 - used execute ruby's functions. accepts 6 arguments.
• this in turn calls vm_call0, accepts 7 arguments.
• this in turn calls vm_call0_body accepts 3 arguments.
• this in turn calls vm_exec (located in vm.c) accepts 1 argument.
• at point i'm bit lost, calls vm_exec_core , lot of other things.

nonetheless hierarchy see ruby pushed quite bit on stack 1 function call: addresses @ least 5 functions , @ least 17 arguments. that's 88 bytes.

that system stack. ruby's vm stack different , belongs ruby's executable rather being managed system. holds structures ruby needs maintain in order execute functions, without incidental boilerplate gets pushed on sytem stack resulting ruby's code structure.