And get rid of the `obj_to_id_tbl`
It's no longer needed, the `object_id` is now stored inline
in the object alongside instance variables.
We still need the inverse table in case `_id2ref` is invoked, but
we lazily build it by walking the heap if that happens.
The `object_id` concern is also no longer a GC implementation
concern, but a generic implementation.
Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>
[Bug #20271]
[Bug #20267]
[Bug #20255]
`rb_obj_alloc(RBASIC_CLASS(obj))` will always allocate from the basic
40B pool, so if `obj` is larger than `40B`, we'll create a corrupted
object when we later copy the shape_id.
Instead we can use the same logic than ractor copy, which is
to use `rb_obj_clone`, and later ask the GC to free the original
object.
We then must turn it into a `T_OBJECT`, because otherwise
just changing its class to `RactorMoved` leaves a lot of
ways to keep using the object, e.g.:
```
a = [1, 2, 3]
Ractor.new{}.send(a, move: true)
[].concat(a) # Should raise, but wasn't.
```
If it turns out that `rb_obj_clone` isn't performant enough
for some uses, we can always have carefully crafted specialized
paths for the types that would benefit from it.
This function replaces the internal rb_obj_gc_flags API. rb_gc_object_metadata
returns an array of name and value pairs, with the last element having
0 for the name.
We have name fragmentation for this feature, including "shared GC",
"modular GC", and "external GC". This commit standardizes the feature
name to "modular GC" and the implementation to "GC library".
Let there be rooms for each GC implementations how to handle multi
threaded situations. They can be totally reentrant, or can have
their own mutex, or can rely on rb_thread_call_with_gvl.
In any ways the allocator (has been, but now officially is)
expected to run properly without a GVL. This means there need be
a way for them to inform the interpreter about their allocation
failures, without relying on raising exceptions.
Let them do so by returning NULL.
So that it doesn't get included in the generated binaries for builds
that don't support loading shared GC modules
Co-Authored-By: Peter Zhu <peter@peterzhu.ca>
Now that we've inlined the eden_heap into the size_pool, we should
rename the size_pool to heap. So that Ruby contains multiple heaps, with
different sized objects.
The term heap as a collection of memory pages is more in memory
management nomenclature, whereas size_pool was a name chosen out of
necessity during the development of the Variable Width Allocation
features of Ruby.
The concept of size pools was introduced in order to facilitate
different sized objects (other than the default 40 bytes). They wrapped
the eden heap and the tomb heap, and some related state, and provided a
reasonably simple way of duplicating all related concerns, to provide
multiple pools that all shared the same structure but held different
objects.
Since then various changes have happend in Ruby's memory layout:
* The concept of tomb heaps has been replaced by a global free pages list,
with each page having it's slot size reconfigured at the point when it
is resurrected
* the eden heap has been inlined into the size pool itself, so that now
the size pool directly controls the free_pages list, the sweeping
page, the compaction cursor and the other state that was previously
being managed by the eden heap.
Now that there is no need for a heap wrapper, we should refer to the
collection of pages containing Ruby objects as a heap again rather than
a size pool
We discovered that having gc.o and gc_impl.o in separate translation
units diminishes codegen quality with GCC 11 on x86-64. This commit
solves that problem by including default/gc.c into gc.c, letting the
optimizer have visibility into the body of functions again in builds
not using link-time optimization, which are common.
This effectively restores things to the way they were before
[Feature #20470] from the optimizer's perspective while maintaining the
ability to build gc/default.c as a DSO.
There were a few functions duplicated across gc.c and gc/default.c.
Extract them and put them into gc/gc.h.
This feature provides a new method `GC.config` that configures internal
GC configuration variables provided by an individual GC implementation.
Implemented in this PR is the option `full_mark`: a boolean value that
will determine whether the Ruby GC is allowed to run a major collection
while the process is running.
It has the following semantics
This feature configures Ruby's GC to only run minor GC's. It's designed
to give users relying on Out of Band GC complete control over when a
major GC is run. Configuring `full_mark: false` does two main things:
* Never runs a Major GC. When the heap runs out of space during a minor
and when a major would traditionally be run, instead we allocate more
heap pages, and mark objspace as needing a major GC.
* Don't increment object ages. We don't promote objects during GC, this
will cause every object to be scanned on every minor. This is an
intentional trade-off between minor GC's doing more work every time,
and potentially promoting objects that will then never be GC'd.
The intention behind not aging objects is that users of this feature
should use a preforking web server, or some other method of pre-warming
the oldgen (like Nakayoshi fork)before disabling Majors. That way most
objects that are going to be old will have already been promoted.
This will interleave major and minor GC collections in exactly the same
what that the Ruby GC runs in versions previously to this. This is the
default behaviour.
* This new method has the following extra semantics:
- `GC.config` with no arguments returns a hash of the keys of the
currently configured GC
- `GC.config` with a key pair (eg. `GC.config(full_mark: true)` sets
the matching config key to the corresponding value and returns the
entire known config hash, including the new values. If the key does
not exist, `nil` is returned
* When a minor GC is run, Ruby sets an internal status flag to determine
whether the next GC will be a major or a minor. When `full_mark:
false` this flag is ignored and every GC will be a minor.
This status flag can be accessed at
`GC.latest_gc_info(:needs_major_by)`. Any value other than `nil` means
that the next collection would have been a major.
Thus it's possible to use this feature to check at a predetermined
time, whether a major GC is necessary and run one if it is. eg. After
a request has finished processing.
```ruby
if GC.latest_gc_info(:needs_major_by)
GC.start(full_mark: true)
end
```
[Feature #20443]
