RFR: 8337217: Port VirtualMemoryTracker to use VMATree [v32]

[Gerard Ziemski]

On Fri, 28 Feb 2025 13:37:32 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> This is a fairly standard pattern in Hotspot, so personally I'm fine with keeping it as-is.
>> 
>> Here's an incomplete list of pre-existing usages:
>> 
>> ```c++
>> // UL tag list
>>   enum type {
>>     __NO_TAG,
>> #define LOG_TAG(name) _##name,
>>     LOG_TAG_LIST
>> #undef LOG_TAG
>>     Count
>>   };
>> 
>> 
>> // enum for figuring positions and size of Symbol::_vm_symbols[]
>> enum class vmSymbolID : int {
>>   // [FIRST_SID ... LAST_SID] is the iteration range for the *valid* symbols.
>>   // NO_SID is used to indicate an invalid symbol. Some implementation code
>>   // *may* read _vm_symbols[NO_SID], so it must be a valid array index.
>>   NO_SID = 0,                // exclusive lower limit
>> 
>>   #define VM_SYMBOL_ENUM(name, string) VM_SYMBOL_ENUM_NAME_(name),
>>   VM_SYMBOLS_DO(VM_SYMBOL_ENUM, VM_ALIAS_IGNORE)
>>   #undef VM_SYMBOL_ENUM
>> 
>>   SID_LIMIT,                 // exclusive upper limit
>> 
>>   #define VM_ALIAS_ENUM(name, def) VM_SYMBOL_ENUM_NAME_(name) = VM_SYMBOL_ENUM_NAME_(def),
>>   VM_SYMBOLS_DO(VM_SYMBOL_IGNORE, VM_ALIAS_ENUM)
>>   #undef VM_ALIAS_ENUM
>> 
>>   FIRST_SID = NO_SID + 1,    // inclusive lower limit
>>   LAST_SID = SID_LIMIT - 1,  // inclusive upper limit
>> };
>> 
>> enum class InjectedFieldID : int {
>>   ALL_INJECTED_FIELDS(DECLARE_INJECTED_FIELD_ENUM)
>>   MAX_enum
>> };
>> 
>> enum class vmClassID : int {
>>   #define DECLARE_VM_CLASS(name, symbol) _VM_CLASS_ENUM(name), _VM_CLASS_ENUM(symbol) = _VM_CLASS_ENUM(name),
>>   VM_CLASSES_DO(DECLARE_VM_CLASS)
>>   #undef DECLARE_VM_CLASS
>> 
>>   LIMIT,             // exclusive upper limit
>>   FIRST = 0,         // inclusive upper limit
>>   LAST = LIMIT - 1   // inclusive upper limit
>> };
>> 
>> enum class CodeBlobType {
>>   MethodNonProfiled   = 0,    // Execution level 1 and 4 (non-profiled) nmethods (including native nmethods)
>>   MethodProfiled      = 1,    // Execution level 2 and 3 (profiled) nmethods
>>   NonNMethod          = 2,    // Non-nmethods like Buffers, Adapters and Runtime Stubs
>>   All                 = 3,    // All types (No code cache segmentation)
>>   NumTypes            = 4     // Number of CodeBlobTypes
>> };
>
> There is coding style that the last enum member counts the number of them, like what we have `mt_number_of_tags` in `MemTag` enum. 
> So, I renamed the last member to `st_number_of_states`. Would it be OK? Or preferred to use constant separately.

Just because we do something already in Hotspot, doesn't necessarily mean that we should repeat the pattern going forward.

I flagged it and I really don't like it, if you guys are OK with it, I will let it be.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1975943416