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

[Johan Sjölen]

On Thu, 27 Feb 2025 18:27:53 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   removed UseFlagInPlace test.
>
> src/hotspot/share/nmt/vmatree.hpp line 73:
> 
>> 71:     assert(type < StateType::COUNT, "must be");
>> 72:     return statetype_strings[static_cast<uint8_t>(type)];
>> 73:   }
> 
> I don't like that we are hardcoding the size of this array and have COUNT be StateType. Can we do something like this?:
> 
> 
>   enum class StateType : uint8_t { Reserved = 1, Committed = 3, Released = 0 };
> 
> private:
>   static constexpr const char* const statetype_strings[] = {"released", "reserved", "only-committed", "committed"};
>   static constexpr int STATETYPE_COUNT = static_cast<int>(sizeof(statetype_strings)/sizeof(char*));
> 
> public:
>   NONCOPYABLE(VMATree);
> 
>   static const char* statetype_to_string(StateType type) {
>     assert(static_cast<uint8_t>(type) < STATETYPE_COUNT, "must be");
>     return statetype_strings[static_cast<uint8_t>(type)];
>   }

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
};

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1975161907