mallocSiteTable.cpp

/*
 * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */
#include "precompiled.hpp"


#include "memory/allocation.inline.hpp"
#include "runtime/atomic.hpp"
#include "services/mallocSiteTable.hpp"

// Malloc site hashtable buckets
MallocSiteHashtableEntry*  MallocSiteTable::_table[MallocSiteTable::table_size];
const NativeCallStack* MallocSiteTable::_hash_entry_allocation_stack = NULL;
const MallocSiteHashtableEntry* MallocSiteTable::_hash_entry_allocation_site = NULL;

// concurrent access counter
volatile int MallocSiteTable::_access_count = 0;

// Tracking hashtable contention
NOT_PRODUCT(int MallocSiteTable::_peak_count = 0;)


/*
 * Initialize malloc site table.
 * Hashtable entry is malloc'd, so it can cause infinite recursion.
 * To avoid above problem, we pre-initialize a hash entry for
 * this allocation site.
 * The method is called during C runtime static variable initialization
 * time, it is in single-threaded mode from JVM perspective.
 */
bool MallocSiteTable::initialize() {
  assert((size_t)table_size <= MAX_MALLOCSITE_TABLE_SIZE, "Hashtable overflow");

  // Fake the call stack for hashtable entry allocation
  assert(NMT_TrackingStackDepth > 1, "At least one tracking stack");

  // Create pseudo call stack for hashtable entry allocation
  address pc[3];
  if (NMT_TrackingStackDepth >= 3) {
    uintx *fp = (uintx*)MallocSiteTable::allocation_at;
    // On ppc64, 'fp' is a pointer to a function descriptor which is a struct  of
    // three native pointers where the first pointer is the real function address.
    // See: http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#FUNC-DES
    pc[2] = (address)(fp PPC64_ONLY(BIG_ENDIAN_ONLY([0])));
  }
  if (NMT_TrackingStackDepth >= 2) {
    uintx *fp = (uintx*)MallocSiteTable::lookup_or_add;
    pc[1] = (address)(fp PPC64_ONLY(BIG_ENDIAN_ONLY([0])));
  }
  uintx *fp = (uintx*)MallocSiteTable::new_entry;
  pc[0] = (address)(fp PPC64_ONLY(BIG_ENDIAN_ONLY([0])));

  static const NativeCallStack stack(pc, MIN2(((int)(sizeof(pc) / sizeof(address))), ((int)NMT_TrackingStackDepth)));
  static const MallocSiteHashtableEntry entry(stack, mtNMT);

  assert(_hash_entry_allocation_stack == NULL &&
         _hash_entry_allocation_site == NULL,
         "Already initailized");

  _hash_entry_allocation_stack = &stack;
  _hash_entry_allocation_site = &entry;

  // Add the allocation site to hashtable.
  int index = hash_to_index(entry.hash());
  _table[index] = const_cast<MallocSiteHashtableEntry*>(&entry);

  return true;
}

// Walks entries in the hashtable.
// It stops walk if the walker returns false.
bool MallocSiteTable::walk(MallocSiteWalker* walker) {
  MallocSiteHashtableEntry* head;
  for (int index = 0; index < table_size; index ++) {
    head = _table[index];
    while (head != NULL) {
      if (!walker->do_malloc_site(head->peek())) {
        return false;
      }
      head = (MallocSiteHashtableEntry*)head->next();
    }
  }
  return true;
}

/*
 *  The hashtable does not have deletion policy on individual entry,
 *  and each linked list node is inserted via compare-and-swap,
 *  so each linked list is stable, the contention only happens
 *  at the end of linked list.
 *  This method should not return NULL under normal circumstance.
 *  If NULL is returned, it indicates:
 *    1. Out of memory, it cannot allocate new hash entry.
 *    2. Overflow hash bucket.
 *  Under any of above circumstances, caller should handle the situation.
 */
MallocSite* MallocSiteTable::lookup_or_add(const NativeCallStack& key, size_t* bucket_idx,
  size_t* pos_idx, MEMFLAGS flags) {
  assert(flags != mtNone, "Should have a real memory type");
  const unsigned int hash = key.calculate_hash();
  const unsigned int index = hash_to_index(hash);
  *bucket_idx = (size_t)index;
  *pos_idx = 0;

  // First entry for this hash bucket
  if (_table[index] == NULL) {
    MallocSiteHashtableEntry* entry = new_entry(key, flags);
    // OOM check
    if (entry == NULL) return NULL;

    // swap in the head
    if (Atomic::replace_if_null(&_table[index], entry)) {
      return entry->data();
    }

    delete entry;
  }

  MallocSiteHashtableEntry* head = _table[index];
  while (head != NULL && (*pos_idx) <= MAX_BUCKET_LENGTH) {
    if (head->hash() == hash) {
      MallocSite* site = head->data();
      if (site->flag() == flags && site->equals(key)) {
        return head->data();
      }
    }

    if (head->next() == NULL && (*pos_idx) < MAX_BUCKET_LENGTH) {
      MallocSiteHashtableEntry* entry = new_entry(key, flags);
      // OOM check
      if (entry == NULL) return NULL;
      if (head->atomic_insert(entry)) {
        (*pos_idx) ++;
        return entry->data();
      }
      // contended, other thread won
      delete entry;
    }
    head = (MallocSiteHashtableEntry*)head->next();
    (*pos_idx) ++;
  }
  return NULL;
}

// Access malloc site
MallocSite* MallocSiteTable::malloc_site(size_t bucket_idx, size_t pos_idx) {
  assert(bucket_idx < table_size, "Invalid bucket index");
  MallocSiteHashtableEntry* head = _table[bucket_idx];
  for (size_t index = 0;
       index < pos_idx && head != NULL;
       index++, head = (MallocSiteHashtableEntry*)head->next()) {}
  assert(head != NULL, "Invalid position index");
  return head->data();
}

// Allocates MallocSiteHashtableEntry object. Special call stack
// (pre-installed allocation site) has to be used to avoid infinite
// recursion.
MallocSiteHashtableEntry* MallocSiteTable::new_entry(const NativeCallStack& key, MEMFLAGS flags) {
  void* p = AllocateHeap(sizeof(MallocSiteHashtableEntry), mtNMT,
    *hash_entry_allocation_stack(), AllocFailStrategy::RETURN_NULL);
  return ::new (p) MallocSiteHashtableEntry(key, flags);
}

void MallocSiteTable::reset() {
  for (int index = 0; index < table_size; index ++) {
    MallocSiteHashtableEntry* head = _table[index];
    _table[index] = NULL;
    delete_linked_list(head);
  }

  _hash_entry_allocation_stack = NULL;
  _hash_entry_allocation_site = NULL;
}

void MallocSiteTable::delete_linked_list(MallocSiteHashtableEntry* head) {
  MallocSiteHashtableEntry* p;
  while (head != NULL) {
    p = head;
    head = (MallocSiteHashtableEntry*)head->next();
    if (p != hash_entry_allocation_site()) {
      delete p;
    }
  }
}

void MallocSiteTable::shutdown() {
  AccessLock locker(&_access_count);
  locker.exclusiveLock();
  reset();
}

bool MallocSiteTable::walk_malloc_site(MallocSiteWalker* walker) {
  assert(walker != NULL, "NuLL walker");
  AccessLock locker(&_access_count);
  if (locker.sharedLock()) {
    NOT_PRODUCT(_peak_count = MAX2(_peak_count, _access_count);)
    return walk(walker);
  }
  return false;
}


void MallocSiteTable::AccessLock::exclusiveLock() {
  int target;
  int val;

  assert(_lock_state != ExclusiveLock, "Can only call once");
  assert(*_lock >= 0, "Can not content exclusive lock");

  // make counter negative to block out shared locks
  do {
    val = *_lock;
    target = _MAGIC_ + *_lock;
  } while (Atomic::cmpxchg(_lock, val, target) != val);

  // wait for all readers to exit
  while (*_lock != _MAGIC_) {
#ifdef _WINDOWS
    os::naked_short_sleep(1);
#else
    os::naked_yield();
#endif
  }
  _lock_state = ExclusiveLock;
}

void MallocSiteTable::print_tuning_statistics(outputStream* st) {

  AccessLock locker(&_access_count);
  if (locker.sharedLock()) {
      // Total number of allocation sites, include empty sites
    int total_entries = 0;
    // Number of allocation sites that have all memory freed
    int empty_entries = 0;
    // Number of captured call stack distribution
    int stack_depth_distribution[NMT_TrackingStackDepth + 1] = { 0 };
    // Chain lengths
    int lengths[table_size] = { 0 };

    for (int i = 0; i < table_size; i ++) {
      int this_chain_length = 0;
      const MallocSiteHashtableEntry* head = _table[i];
      while (head != NULL) {
        total_entries ++;
        this_chain_length ++;
        if (head->size() == 0) {
          empty_entries ++;
        }
        const int callstack_depth = head->peek()->call_stack()->frames();
        assert(callstack_depth >= 0 && callstack_depth <= NMT_TrackingStackDepth,
               "Sanity (%d)", callstack_depth);
        stack_depth_distribution[callstack_depth] ++;
        head = head->next();
      }
      lengths[i] = this_chain_length;
    }

    st->print_cr("Malloc allocation site table:");
    st->print_cr("\tTotal entries: %d", total_entries);
    st->print_cr("\tEmpty entries: %d (%2.2f%%)", empty_entries, ((float)empty_entries * 100) / total_entries);
    st->cr();

    // We report the hash distribution (chain length distribution) of the n shortest chains
    //  - under the assumption that this usually contains all lengths. Reporting threshold
    //  is 20, and the expected avg chain length is 5..6 (see table size).
    static const int chain_length_threshold = 20;
    int chain_length_distribution[chain_length_threshold] = { 0 };
    int over_threshold = 0;
    int longest_chain_length = 0;
    for (int i = 0; i < table_size; i ++) {
      if (lengths[i] >= chain_length_threshold) {
        over_threshold ++;
      } else {
        chain_length_distribution[lengths[i]] ++;
      }
      longest_chain_length = MAX2(longest_chain_length, lengths[i]);
    }

    st->print_cr("Hash distribution:");
    if (chain_length_distribution[0] == 0) {
      st->print_cr("no empty buckets.");
    } else {
      st->print_cr("%d buckets are empty.", chain_length_distribution[0]);
    }
    for (int len = 1; len < MIN2(longest_chain_length + 1, chain_length_threshold); len ++) {
      st->print_cr("%2d %s: %d.", len, (len == 1 ? "  entry" : "entries"), chain_length_distribution[len]);
    }
    if (longest_chain_length >= chain_length_threshold) {
      st->print_cr(">=%2d entries: %d.", chain_length_threshold, over_threshold);
    }
    st->print_cr("most entries: %d.", longest_chain_length);
    st->cr();

    st->print_cr("Call stack depth distribution:");
    for (int i = 0; i <= NMT_TrackingStackDepth; i ++) {
      st->print_cr("\t%d: %d", i, stack_depth_distribution[i]);
    }
    st->cr();
  } // lock
}


bool MallocSiteHashtableEntry::atomic_insert(MallocSiteHashtableEntry* entry) {
  return Atomic::replace_if_null(&_next, entry);
}