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
These methods are removed from gc.rb and added to gc.c:
- GC.compact
- GC.auto_compact
- GC.auto_compact=
- GC.latest_compact_info
- GC.verify_compaction_references
This is a prefactor to allow setting these methods to
`rb_f_notimplement` in a followup commit.
* `GC.measure_total_time = true` enables total time measurement (default: true)
* `GC.measure_total_time` returns current flag.
* `GC.total_time` returns measured total time in nano seconds.
* `GC.stat(:time)` (and Hash) returns measured total time in milli seconds.
Both explicit compaction routines (gc_compact and the verify references form)
need to clear the heap before executing compaction. Otherwise some
objects may not be alive, and we'll need the read barrier. The heap
must only contain *live* objects if we want to disable the read barrier
during explicit compaction.
The previous commit was missing the "clear the heap" phase from the
"verify references" explicit compaction function.
Fixes [Bug #17306]
* `GC.auto_compact=`, `GC.auto_compact` can be used to control when
compaction runs. Setting `auto_compact=` to true will cause
compaction to occurr duing major collections. At the moment,
compaction adds significant overhead to major collections, so please
test first!
[Feature #17176]
This reverts commit 02b216e5a7.
This reverts commit 9b8825b6f9.
I found that combining sweep and move is not safe. I don't think that
we can do compaction concurrently with _anything_ unless there is a read
barrier installed.
Here is a simple example. A class object is freed, and during it's free
step, it tries to remove itself from its parent's subclass list.
However, during the sweep step, the parent class was moved and the
"currently being freed" class didn't have references updated yet. So we
get a segv like this:
```
(lldb) bt
* thread #1, name = 'ruby', stop reason = signal SIGSEGV
* frame #0: 0x0000560763e344cb ruby`rb_st_lookup at st.c:320:43
frame #1: 0x0000560763e344cb ruby`rb_st_lookup(tab=0x2f7469672f6e6f72, key=3809, value=0x0000560765bf2270) at st.c:1010
frame #2: 0x0000560763e8f16a ruby`rb_search_class_path at variable.c:99:9
frame #3: 0x0000560763e8f141 ruby`rb_search_class_path at variable.c:145
frame #4: 0x0000560763e8f141 ruby`rb_search_class_path(klass=94589785585880) at variable.c:191
frame #5: 0x0000560763ec744e ruby`rb_vm_bugreport at vm_dump.c:996:17
frame #6: 0x0000560763f5b958 ruby`rb_bug_for_fatal_signal at error.c:675:5
frame #7: 0x0000560763e27dad ruby`sigsegv(sig=<unavailable>, info=<unavailable>, ctx=<unavailable>) at signal.c:955:5
frame #8: 0x00007f8b891d33c0 libpthread.so.0`___lldb_unnamed_symbol1$$libpthread.so.0 + 1
frame #9: 0x0000560763efa8bb ruby`rb_class_remove_from_super_subclasses(klass=94589790314280) at class.c:93:56
frame #10: 0x0000560763d10cb7 ruby`gc_sweep_step at gc.c:2674:2
frame #11: 0x0000560763d1187b ruby`gc_sweep at gc.c:4540:2
frame #12: 0x0000560763d101f0 ruby`gc_start at gc.c:6797:6
frame #13: 0x0000560763d15153 ruby`rb_gc_compact at gc.c:7479:12
frame #14: 0x0000560763eb4eb8 ruby`vm_exec_core at vm_insnhelper.c:5183:13
frame #15: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
frame #16: 0x0000560763eac08d ruby`rb_yield at vm.c:1132:9
frame #17: 0x0000560763edb4f2 ruby`rb_ary_collect at array.c:3186:9
frame #18: 0x0000560763e9ee15 ruby`vm_call_cfunc_with_frame at vm_insnhelper.c:2575:12
frame #19: 0x0000560763eb2e66 ruby`vm_exec_core at vm_insnhelper.c:4177:11
frame #20: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
frame #21: 0x0000560763eac08d ruby`rb_yield at vm.c:1132:9
frame #22: 0x0000560763edb4f2 ruby`rb_ary_collect at array.c:3186:9
frame #23: 0x0000560763e9ee15 ruby`vm_call_cfunc_with_frame at vm_insnhelper.c:2575:12
frame #24: 0x0000560763eb2e66 ruby`vm_exec_core at vm_insnhelper.c:4177:11
frame #25: 0x0000560763ea9bae ruby`rb_vm_exec at vm.c:1953:22
frame #26: 0x0000560763ceee01 ruby`rb_ec_exec_node(ec=0x0000560765afa530, n=0x0000560765b088e0) at eval.c:296:2
frame #27: 0x0000560763cf3b7b ruby`ruby_run_node(n=0x0000560765b088e0) at eval.c:354:12
frame #28: 0x0000560763cee4a3 ruby`main(argc=<unavailable>, argv=<unavailable>) at main.c:50:9
frame #29: 0x00007f8b88e560b3 libc.so.6`__libc_start_main + 243
frame #30: 0x0000560763cee4ee ruby`_start + 46
(lldb) f 9
frame #9: 0x0000560763efa8bb ruby`rb_class_remove_from_super_subclasses(klass=94589790314280) at class.c:93:56
90
91 *RCLASS_EXT(klass)->parent_subclasses = entry->next;
92 if (entry->next) {
-> 93 RCLASS_EXT(entry->next->klass)->parent_subclasses = RCLASS_EXT(klass)->parent_subclasses;
94 }
95 xfree(entry);
96 }
(lldb) command script import -r misc/lldb_cruby.py
lldb scripts for ruby has been installed.
(lldb) rp entry->next->klass
(struct RMoved) $1 = (flags = 30, destination = 94589792806680, next = 94589784369160)
(lldb)
```
This commit combines the sweep step with moving objects. With this
commit, we can do:
```ruby
GC.start(compact: true)
```
This code will do the following 3 steps:
1. Fully mark the heap
2. Sweep + Move objects
3. Update references
By default, this will compact in order that heap pages are allocated.
In other words, objects will be packed towards older heap pages (as
opposed to heap pages with more pinned objects like `GC.compact` does).
Add a description about optional hash objects for GC.stat and
GC.latest_gc_info. [Bug #14408]
The patch is provided by sho-h (Sho Hashimoto).
Thank you so much.
Matt Valentine-House
Nobuyoshi Nakada
Mike Dalessio
Peter Zhu
zverok
Koichi Sasada
Jemma Issroff
Aaron Patterson
Kazuhiro NISHIYAMA