We can loosely predict the number of ivar sets on a class based on the
number of iv set instructions in the initialize method. This should give
us a more accurate estimate to use for initial size pool allocation,
which should in turn give us more cache hits.
This commit adds RVALUE_OVERHEAD for storing metadata at the end of the
slot. This commit moves the ractor_belonging_id in debug builds from the
flags to RVALUE_OVERHEAD which frees the 16 bits in the headers for
object shapes.
We would like to differentiate types of objects via their shape. This
commit adds a special T_OBJECT shape when we allocate an instance of
T_OBJECT. This allows us to avoid testing whether an object is an
instance of a T_OBJECT or not, we can just check the shape.
Since object shapes store the capacity of an object, we no longer
need the numiv field on RObjects. This gives us one extra slot which
we can use to give embedded objects one more instance variable (for a
total of 3 ivs). This commit removes the concept of numiv from RObject.
This commit adds a `capacity` field to shapes, and adds shape
transitions whenever an object's capacity changes. Objects which are
allocated out of a bigger size pool will also make a transition from the
root shape to the shape with the correct capacity for their size pool
when they are allocated.
This commit will allow us to remove numiv from objects completely, and
will also mean we can guarantee that if two objects share shapes, their
IVs are in the same positions (an embedded and extended object cannot
share shapes). This will enable us to implement ivar sets in YJIT using
object shapes.
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
fiber machine stack is placed outside of C stack allocated by wasm-ld,
so highest stack address recorded by `rb_wasm_record_stack_base` is
invalid when running on non-main fiber.
Therefore, we should scan `stack_{start,end}` which always point a valid
stack range in any context.
We were previously incrementing the max_iv_count on a class in gc
freeing. By the time we free an object though, we're not guaranteed its
class is still valid. Instead, we can do this when marking and we're
guaranteed the object still knows its class.
* Avoid RCLASS_IV_TBL in marshal.c
* Avoid RCLASS_IV_TBL for class names
* Avoid RCLASS_IV_TBL for autoload
* Avoid RCLASS_IV_TBL for class variables
* Avoid copying RCLASS_IV_TBL onto ICLASSes
* Use object shapes for Class and Module IVs
`iv_count` is a misleading name because when IVs are unset, the new
shape doesn't decrement this value. `next_iv_count` is an accurate, and
more descriptive name.
Before object shapes, we were using class serial to invalidate
inline caches. Now that we use shape_id for inline cache keys,
the class serial is unnecessary.
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Shapes gives us an almost exact count of instance variables on an
object. Since we know the number of instance variables that have been
set, we will never access slots that haven't been initialized with an
IV.
Shapes provides us with an (almost) exact count of instance variables.
We only need to check for Qundef when an IV has been "undefined"
Prefer to use ROBJECT_IV_COUNT when iterating IVs
GCC 12 introduced a new warning flag `-Wuse-after-free`, however it
has a false positive at `realloc` when optimization is disabled, since
the memory requested for reallocation is guaranteed to not be touched.
This workaround is very unclear why the false warning is suppressed by
a statement-expression GCC extension.
Object Shapes is used for accessing instance variables and representing the
"frozenness" of objects. Object instances have a "shape" and the shape
represents some attributes of the object (currently which instance variables are
set and the "frozenness"). Shapes form a tree data structure, and when a new
instance variable is set on an object, that object "transitions" to a new shape
in the shape tree. Each shape has an ID that is used for caching. The shape
structure is independent of class, so objects of different types can have the
same shape.
For example:
```ruby
class Foo
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
class Bar
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
foo = Foo.new # `foo` has shape id 2
bar = Bar.new # `bar` has shape id 2
```
Both `foo` and `bar` instances have the same shape because they both set
instance variables of the same name in the same order.
This technique can help to improve inline cache hits as well as generate more
efficient machine code in JIT compilers.
This commit also adds some methods for debugging shapes on objects. See
`RubyVM::Shape` for more details.
For more context on Object Shapes, see [Feature: #18776]
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: Eileen M. Uchitelle <eileencodes@gmail.com>
Co-Authored-By: John Hawthorn <john@hawthorn.email>
Tabs were expanded because the file did not have any tab indentation in unedited lines.
Please update your editor config, and use misc/expand_tabs.rb in the pre-commit hook.
Object Shapes is used for accessing instance variables and representing the
"frozenness" of objects. Object instances have a "shape" and the shape
represents some attributes of the object (currently which instance variables are
set and the "frozenness"). Shapes form a tree data structure, and when a new
instance variable is set on an object, that object "transitions" to a new shape
in the shape tree. Each shape has an ID that is used for caching. The shape
structure is independent of class, so objects of different types can have the
same shape.
For example:
```ruby
class Foo
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
class Bar
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
foo = Foo.new # `foo` has shape id 2
bar = Bar.new # `bar` has shape id 2
```
Both `foo` and `bar` instances have the same shape because they both set
instance variables of the same name in the same order.
This technique can help to improve inline cache hits as well as generate more
efficient machine code in JIT compilers.
This commit also adds some methods for debugging shapes on objects. See
`RubyVM::Shape` for more details.
For more context on Object Shapes, see [Feature: #18776]
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: Eileen M. Uchitelle <eileencodes@gmail.com>
Co-Authored-By: John Hawthorn <john@hawthorn.email>
Poisoned regions cannot be accessed without unpoisoning outside gc.c.
Specifically, debug.gem is terminated by AddressSanitizer.
```
SUMMARY: AddressSanitizer: use-after-poison iseq_collector.c:39 in iseq_i
```
Tabs were expanded because the file did not have any tab indentation in unedited lines.
Please update your editor config, and use misc/expand_tabs.rb in the pre-commit hook.
rb_ary_tmp_new suggests that the array is temporary in some way, but
that's not true, it just creates an array that's hidden and not on the
transient heap. This commit renames it to rb_ary_hidden_new.
Before this commit, if we don't have enough slots after sweeping but
had pages on the tomb heap, then the GC would frequently allocate and
deallocate pages. This is because after sweeping it would set
allocatable pages (since there were not enough slots) but free the
pages on the tomb heap.
This commit reuses pages on the tomb heap if there's not enough slots
after sweeping.
Prior to this commit it was possible to call `ObjectSpace._id2ref` with
an offset static symbol object_id and get back a new, incorrectly tagged
symbol:
```
> sensible_sym = ObjectSpace._id2ref(:a.object_id)
=> :a
> nonsense_sym = ObjectSpace._id2ref(:a.object_id + 40)
=> :a
> sensible_sym == nonsense_sym
=> false
```
`nonsense_sym` ends up tagged with `RUBY_ID_INSTANCE` instead of
`RB_ID_LOCAL`. That means we can do silly things like:
```
> foo = Object.new
> foo.instance_variable_set(:a, 123)
(irb):2:in `instance_variable_set': `a' is not allowed as an instance variable name (NameError)
> foo.instance_variable_set(ObjectSpace._id2ref(:a.object_id + 40), 123)
=> 123
> foo.instance_variables
=> [:a]
```
This was happening because `get_id_entry` ignores the tag bits when
looking up the symbol. So `rb_id2str(symid)` would return a value and
then we'd continue on with the nonsense `symid`.
This commit prevents the situation by checking that the `symid` actually
matches what we get back from `get_id_entry`. Now we get a `RangeError`
for the nonsense id:
```
> ObjectSpace._id2ref(:a.object_id)
=> :a
> ObjectSpace._id2ref(:a.object_id + 40)
(irb):1:in `_id2ref': 0x000000000013f408 is not symbol id value (RangeError)
```
Co-authored-by: John Hawthorn <jhawthorn@github.com>
In wmap_live_p, if is_pointer_to_heap returns false, then the page is
either in the tomb or has already been freed, so the object is dead. In
this case, wmap_live_p should return false.
This commit implements Objects on Variable Width Allocation. This allows
Objects with more ivars to be embedded (i.e. contents directly follow the
object header) which improves performance through better cache locality.
This commit enables Arrays to move between size pools during compaction.
This can occur if the array is mutated such that it would fit in a
different size pool when embedded.
The move is carried out in two stages:
1. The RVALUE is moved to a destination heap during object movement
phase of compaction
2. The array data is re-embedded and the original buffer free'd if
required. This happens during the update references step
In order to reliably test compaction we need to be able to move objects
between size pools.
In order for this to happen there must be pages in a size pool into
which we can allocate.
The existing implementation of `double_heap` only doubled the existing
number of pages in the heap, so if a size pool had a low number of pages
(or 0) it's not guaranteed that enough space will be created to move
objects into that size pool.
This commit deprecates the `double_heap` option and replaces it with
`expand_heap` instead.
expand heap will expand each heap by enough pages to hold a number of
slots defined by `GC_HEAP_INIT_SLOTS` or by `heap->total_pags` whichever
is larger.
If both `double_heap` and `expand_heap` are present, a deprecation
warning will be shown for `double_heap` and the `expand_heap` behaviour
will take precedence
Given that this is an API intended for debugging and testing GC
compaction I'm not concerned about the extra memory usage or time taken
to create the pages. However, for completeness:
Running the following `test.rb` and using `time` on my Macbook Pro shows
the following memory usage and time impact:
pp "RSS (kb): #{`ps -o rss #{Process.pid}`.lines.last.to_i}"
GC.verify_compaction_references(double_heap: true, toward: :empty)
pp "RSS (kb): #{`ps -o rss #{Process.pid}`.lines.last.to_i}"
❯ time make run
./miniruby -I./lib -I. -I.ext/common -r./arm64-darwin21-fake ./test.rb
"RSS (kb): 24000"
<internal:gc>:251: warning: double_heap is deprecated and will be removed
"RSS (kb): 25232"
________________________________________________________
Executed in 124.37 millis fish external
usr time 82.22 millis 0.09 millis 82.12 millis
sys time 28.76 millis 2.61 millis 26.15 millis
❯ time make run
./miniruby -I./lib -I. -I.ext/common -r./arm64-darwin21-fake ./test.rb
"RSS (kb): 24000"
"RSS (kb): 49040"
________________________________________________________
Executed in 150.13 millis fish external
usr time 103.32 millis 0.10 millis 103.22 millis
sys time 35.73 millis 2.59 millis 33.14 millis
Jemma Issroff
Peter Zhu
Aaron Patterson
S-H-GAMELINKS
Yuta Saito
John Hawthorn
Nobuyoshi Nakada
Sergey Fedorov
Samuel Williams
git
Takashi Kokubun
Daniel Colson
Matt Valentine-House