[ruby-core:117432] [Ruby master Feature#20408] Add heap_live_slots to GC.stat_heap

[ruby-core:117432] [Ruby master Feature#20408] Add heap_live_slots to GC.stat_heap

[mk via ruby-core]

Issue #20408 has been reported by mk (Matthias Käppler).

----------------------------------------
Feature #20408: Add heap_live_slots to GC.stat_heap
https://bugs.ruby-lang.org/issues/20408

* Author: mk (Matthias Käppler)
* Status: Open
----------------------------------------
`GC.stat` exposes a `heap_live_slots` metric that returns the number of live objects occupying eden slots.

Because the slot size was fixed to `RVALUE_SIZE`, this allowed for some basic approximations of how many bytes were live/in-use (`heap_live_slots * RVALUE_SIZE`).
This could furthermore be "embellished" by adding malloc'ed memory for those objects that were larger than a 40B slot (we track this via a custom CRuby patch).

However, with the addition of Variable Width Allocations (https://bugs.ruby-lang.org/issues/18239), this does not work anymore because we don't know how `heap_live_slots` distributes over all pools that use different slot sizes.

This could be addressed by also adding `heap_live_slots` (and for symmetry: `heap_free_slots`) to `GC.stat_heap`.
The sum of all live slots per pool times its respective slot size should equal `GC.stat[:heap_live_slots]`.



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[ruby-core:117433] [Ruby master Feature#20408] Add heap_live_slots to GC.stat_heap

[peterzhu2118 (Peter Zhu) via ruby-core]

Issue #20408 has been updated by peterzhu2118 (Peter Zhu).


Thank you for this ticket. I opened a PR that implements this feature: https://github.com/ruby/ruby/pull/10439

----------------------------------------
Feature #20408: Add heap_live_slots to GC.stat_heap
https://bugs.ruby-lang.org/issues/20408#change-107810

* Author: mk (Matthias Käppler)
* Status: Open
----------------------------------------
`GC.stat` exposes a `heap_live_slots` metric that returns the number of live objects occupying eden slots.

Because the slot size was fixed to `RVALUE_SIZE`, this allowed for some basic approximations of how many bytes were live/in-use (`heap_live_slots * RVALUE_SIZE`).
This could furthermore be "embellished" by adding malloc'ed memory for those objects that were larger than a 40B slot (we track this via a custom CRuby patch).

However, with the addition of Variable Width Allocations (https://bugs.ruby-lang.org/issues/18239), this does not work anymore because we don't know how `heap_live_slots` distributes over all pools that use different slot sizes.

This could be addressed by also adding `heap_live_slots` (and for symmetry: `heap_free_slots`) to `GC.stat_heap`. The sum of all live slots per pool should equal `GC.stat[:heap_live_slots]`.



-- 
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 ______________________________________________
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 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
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[ruby-core:117440] [Ruby master Feature#20408] Add heap_live_slots to GC.stat_heap

[mk via ruby-core]

Issue #20408 has been updated by mk (Matthias Käppler).


peterzhu2118 (Peter Zhu) wrote in #note-2:
> Thank you for this ticket. I opened a PR that implements this feature: https://github.com/ruby/ruby/pull/10439

Thank you so much Peter! <3

----------------------------------------
Feature #20408: Add heap_live_slots to GC.stat_heap
https://bugs.ruby-lang.org/issues/20408#change-107819

* Author: mk (Matthias Käppler)
* Status: Open
----------------------------------------
`GC.stat` exposes a `heap_live_slots` metric that returns the number of live objects occupying eden slots.

Because the slot size was fixed to `RVALUE_SIZE`, this allowed for some basic approximations of how many bytes were live/in-use (`heap_live_slots * RVALUE_SIZE`).
This could furthermore be "embellished" by adding malloc'ed memory for those objects that were larger than a 40B slot (we track this via a custom CRuby patch).

However, with the addition of Variable Width Allocations (https://bugs.ruby-lang.org/issues/18239), this does not work anymore because we don't know how `heap_live_slots` distributes over all pools that use different slot sizes.

This could be addressed by also adding `heap_live_slots` (and for symmetry: `heap_free_slots`) to `GC.stat_heap`. The sum of all live slots per pool should equal `GC.stat[:heap_live_slots]`.



-- 
https://bugs.ruby-lang.org/
 ______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
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