RFR: 8253064: monitor list simplifications and getting rid of TSM

[Daniel D.Daugherty]

On Mon, 2 Nov 2020 22:13:30 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Changes from @fisk and @dcubed-ojdk to:
>> 
>> - simplify ObjectMonitor list management
>> - get rid of Type-Stable Memory (TSM)
>> 
>> This change has been tested with Mach5 Tier[1-3],4,5,6,7,8; no new regressions.
>> Aurora Perf runs have also been done (DaCapo-h2, Quick Startup/Footprint,
>> SPECjbb2015-Tuned-G1, SPECjbb2015-Tuned-ParGC, Volano)
>>   - a few minor regressions (<= -0.24%)
>>   - Volano is 6.8% better
>> 
>> Eric C. has also running promotion perf runs on these bits and says "the results look fine".
>
> Self review done.

### Gory details about these changes from @fisk and @dcubed-ojdk:

### Simplify `ObjectMonitor` List Management:

- delete per-thread in-use and free-lists.
- delete global free-list and global wait-list; there is a still a global in-use list; after `ObjectMonitor`s on the global in-use list are deflated, they are unlinked and added to a function local `GrowableArray` called `delete_list`; we do a handshake/safepoint with all JavaThreads and that makes all the `ObjectMonitor`s on the `delete_list` safe for deletion; lastly, we delete all the `ObjectMonitor`s on `delete_list`.
- move async deflation work from the `ServiceThread` to a dedicated `MonitorDeflationThread`; this prevents `ObjectMonitor` inflation storms from delaying the work done by the `ServiceThread` for other subsystems; this means the `ServiceThread` no longer wakes up every `GuaranteedSafepointInterval` to check for work.
- the `AllocationState` enum is dropped along with the  `_allocation_state` field and associated getters and setters; the simpler list management no longer requires the allocation state to be tracked.
- the safepoint cleanup phase no longer requests async monitor deflation; there is no longer a safepoint cleanup task for monitor deflation, but there is still an auditing/logging hook for debugging purposes.
- delete ObjectSynchronizer functions associated with more complicated list management: `deflate_global_idle_monitors()`, `deflate_per_thread_idle_monitors()`, `deflate_common_idle_monitors()`, `om_flush()`, `prepend_list_to_common()`, `prepend_list_to_global_free_list()`, `prepend_list_to_global_wait_list()`, `prepend_list_to_global_in_use_list()`, `prepend_to_common()`, `prepend_to_om_free_list()`, `prepend_to_om_in_use_list()`, `take_from_start_of_common()`, `take_from_start_of_global_free_list()`, `take_from_start_of_om_free_list()`
- delete the spin-lock functions needed by the more complicated list management.
- delete a number of audit/debug/logging related functions needed by the more complicated list management.
- restore the barrier related code that needed relocation due to om_flush()'s access of the weak obj reference; now that om_flush() is gone, the barrier related code can go back to its more natural place.

### Get Rid of Type-Stable Memory (TSM):

- `ObjectMonitor` now subclasses `CHeapObj<mtInternal>`.
- the `ObjectMonitor` constructor and destructor are now more normal C++!
- delete `ObjectMonitor` functions associated with TSM: `clear()`, `clear_common()`, `object_addr()`, `Recycle()`, and `set_object()`.
- delete the version of `set_owner_from()` that support two possible old values since it is no longer needed; we are not recycling deflated `ObjectMonitor`s anymore so there's no longer a possibility of a `NULL` `_owner` value or a `DEFLATER_MARKER` value on the same code path.
- delete ObjectSynchronizer functions associated with TSM: `om_alloc()`, `om_release()`, `prepend_block_to_lists()`
- simplify ObjectSynchronizer functions related to TSM: `deflate_idle_monitors()`, `deflate_monitor_list()`, `inflate()`

### Change A Displaced Header is Always at Offset 0

- Change `markWord::displaced_mark_helper()` and `markWord::set_displaced_mark_helper()` to no longer assume that the displaced header in a `BasicLock` or `ObjectMonitor` is at offset 0.
- ObjectMonitor::header_addr() no longer requires the offset to be zero.

### New Diagnostic Options

- `AvgMonitorsPerThreadEstimate` - Used to estimate a variable ceiling based on number of threads for use with `MonitorUsedDeflationThreshold`; default is 1024, 0 is off, range is 0..max_jint. The current count of inflated `ObjectMonitor`s and the ceiling are used to determine whether the in-use ratio is higher than `MonitorUsedDeflationThreshold` (default 90).
- `MonitorDeflationMax` - The maximum number of `ObjectMonitor`s to deflate, unlink and delete at one time; default is 1 million; range is 1024..max_jint.

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PR: https://git.openjdk.java.net/jdk/pull/642