src/hotspot/os/linux/hugepages.hpp

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#ifndef OS_LINUX_HUGEPAGES_HPP
#define OS_LINUX_HUGEPAGES_HPP

#include "memory/allStatic.hpp"
#include "runtime/os.hpp" // for os::PageSizes
#include "utilities/globalDefinitions.hpp"

class outputStream;

// Header contains the interface that reads OS information about
// available hugepage support:
// - class StaticHugePageSupport - about static (non-THP) hugepages
// - class THPSupport - about transparent huge pages
// and:
// - class HugePages - a static umbrella wrapper

// Information about static (non-thp) hugepages
class StaticHugePageSupport {
  bool _initialized;

  // All supported hugepage sizes (sizes for which entries exist
  // in /sys/kernel/mm/hugepages/hugepage-xxx)
  os::PageSizes _pagesizes;

  // Contains the default hugepage. The "default hugepage size" is the one that
  // - is marked in /proc/meminfo as "Hugepagesize"
  // - is the size one gets when using mmap(MAP_HUGETLB) when omitting size specifiers like MAP_HUGE_SHIFT)
  size_t _default_hugepage_size;

  // If true, the kernel support for hugepages is inconsistent
  bool _inconsistent;

public:
  StaticHugePageSupport();

  void scan_os();

  os::PageSizes pagesizes() const;
  size_t default_hugepage_size() const;
  void print_on(outputStream* os);

  bool inconsistent() const { return _inconsistent; }
};

enum class THPMode { always, never, madvise };

// 2) for transparent hugepages
class THPSupport {
  bool _initialized;

  // See /sys/kernel/mm/transparent_hugepages/enabled
  THPMode _mode;

  // Contains the THP page size
  size_t _pagesize;

public:

  THPSupport();

  // Queries the OS, fills in object
  void scan_os();

  THPMode mode() const;
  size_t pagesize() const;
  void print_on(outputStream* os);
};

// Umbrella static interface
class HugePages : public AllStatic {

  static StaticHugePageSupport _static_hugepage_support;
  static THPSupport _thp_support;

public:

  static const StaticHugePageSupport& static_info() { return _static_hugepage_support; }
  static const THPSupport& thp_info() { return _thp_support; }

  static size_t default_static_hugepage_size()  { return _static_hugepage_support.default_hugepage_size(); }
  static bool supports_static_hugepages()       { return default_static_hugepage_size() > 0 && !_static_hugepage_support.inconsistent(); }
  static THPMode thp_mode()                     { return _thp_support.mode(); }
  static bool supports_thp()                    { return thp_mode() == THPMode::madvise || thp_mode() == THPMode::always; }
  static size_t thp_pagesize()                  { return _thp_support.pagesize(); }

  static void initialize();
  static void print_on(outputStream* os);
};

#endif // OS_LINUX_HUGEPAGES_HPP