[ruby-core:95289] [Ruby master Feature#16245] Add interfaces to count and measure size all IMEMO objects

[sam.saffron@gmail.com]

Issue #16245 has been updated by sam.saffron (Sam Saffron).


To be honest I think the best spot for this is `RubyVM.stat`

perhaps:

```
RubyVM.stat
{
   :global_method_state=>143, 
   :global_constant_state=>1369, 
   :class_serial=>8768,
   :imemo_ment_count,
   :imemo_iseq_count,
   :imemo_env_count,
   :imemo_tmpbuf_count,
   :imemo_ast_count,
   :imemo_ment_size,
   :imemo_iseq_size,
   :imemo_env_size,
   :imemo_tmpbuf_size,
   :imemo_ast_size
}
```

Since `RubyVM.stat(:class_serial)` is already supported as an efficient way to grab a single metric this interface fits nicely. It does not expand the signature surface of Ruby and is something that would be very simple to add for 2.7. 


Additionally for extra bonus points: 


RubyVM.stat(:total_allocated_bytes): all the bytes Ruby xmalloc and family allocated since process start
RubyVM.stat(:total_freed_bytes): all the bytes freed


This comprehensive set of changes would make introspection of "why is my Ruby size XYZ?" really easy and provide some extremely powerful metrics for graphing.

Thoughts? 

----------------------------------------
Feature #16245: Add interfaces to count and measure size all IMEMO objects
https://bugs.ruby-lang.org/issues/16245#change-81969

* Author: sam.saffron (Sam Saffron)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Koichi introduced an experimental gem: https://github.com/ko1/iseq_collector

It allows:

ObjectSpace.each_iseq{|iseq| ...}
ObjectSpace.count_iseq #=> Integer
ObjectSpace.memsize_of_all_iseq (should not generate RubyVM::InstructionSequence wrappers for IMEMOs)

Since the wrapper object  RubyVM::InstructionSequence is lazily allocated, ObjectSpace.each_object does not find these IMEMOs unless they have been wrapped. This design is good and conserves memory. 

`count_iseq` and `memsize_of_all_iseq` are very powerful metrics most large Ruby deployments can use to automatically detect method leaks introduced via meta programming. These issues are invisible now short of walking a heap dump. 

Can we add the new interface into 2.7?



-- 
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