// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Sanjay Ghemawat <opensource@google.com>
#include "config.h"
#include "common.h"
#include "system-alloc.h"
namespace tcmalloc {
// Note: the following only works for "n"s that fit in 32-bits, but
// that is fine since we only use it for small sizes.
static inline int LgFloor(size_t n) {
int log = 0;
for (int i = 4; i >= 0; --i) {
int shift = (1 << i);
size_t x = n >> shift;
if (x != 0) {
n = x;
log += shift;
}
}
ASSERT(n == 1);
return log;
}
int AlignmentForSize(size_t size) {
int alignment = kAlignment;
if (size > kMaxSize) {
// Cap alignment at kPageSize for large sizes.
alignment = kPageSize;
} else if (size >= 128) {
// Space wasted due to alignment is at most 1/8, i.e., 12.5%.
alignment = (1 << LgFloor(size)) / 8;
} else if (size >= 16) {
// We need an alignment of at least 16 bytes to satisfy
// requirements for some SSE types.
alignment = 16;
}
// Maximum alignment allowed is page size alignment.
if (alignment > kPageSize) {
alignment = kPageSize;
}
CHECK_CONDITION(size < 16 || alignment >= 16);
CHECK_CONDITION((alignment & (alignment - 1)) == 0);
return alignment;
}
int SizeMap::NumMoveSize(size_t size) {
if (size == 0) return 0;
// Use approx 64k transfers between thread and central caches.
int num = static_cast<int>(64.0 * 1024.0 / size);
if (num < 2) num = 2;
// Avoid bringing too many objects into small object free lists.
// If this value is too large:
// - We waste memory with extra objects sitting in the thread caches.
// - The central freelist holds its lock for too long while
// building a linked list of objects, slowing down the allocations
// of other threads.
// If this value is too small:
// - We go to the central freelist too often and we have to acquire
// its lock each time.
// This value strikes a balance between the constraints above.
if (num > 32) num = 32;
return num;
}
// Initialize the mapping arrays
void SizeMap::Init() {
// Do some sanity checking on add_amount[]/shift_amount[]/class_array[]
if (ClassIndex(0) < 0) {
Log(kCrash, __FILE__, __LINE__,
"Invalid class index for size 0", ClassIndex(0));
}
if (ClassIndex(kMaxSize) >= sizeof(class_array_)) {
Log(kCrash, __FILE__, __LINE__,
"Invalid class index for kMaxSize", ClassIndex(kMaxSize));
}
// Compute the size classes we want to use
int sc = 1; // Next size class to assign
int alignment = kAlignment;
CHECK_CONDITION(kAlignment <= 16);
for (size_t size = kAlignment; size <= kMaxSize; size += alignment) {
alignment = AlignmentForSize(size);
CHECK_CONDITION((size % alignment) == 0);
int blocks_to_move = NumMoveSize(size) / 4;
size_t psize = 0;
do {
psize += kPageSize;
// Allocate enough pages so leftover is less than 1/8 of total.
// This bounds wasted space to at most 12.5%.
while ((psize % size) > (psize >> 3)) {
psize += kPageSize;
}
// Continue to add pages until there are at least as many objects in
// the span as are needed when moving objects from the central
// freelists and spans to the thread caches.
} while ((psize / size) < (blocks_to_move));
const size_t my_pages = psize >> kPageShift;
if (sc > 1 && my_pages == class_to_pages_[sc-1]) {
// See if we can merge this into the previous class without
// increasing the fragmentation of the previous class.
const size_t my_objects = (my_pages << kPageShift) / size;
const size_t prev_objects = (class_to_pages_[sc-1] << kPageShift)
/ class_to_size_[sc-1];
if (my_objects == prev_objects) {
// Adjust last class to include this size
class_to_size_[sc-1] = size;
continue;
}
}
// Add new class
class_to_pages_[sc] = my_pages;
class_to_size_[sc] = size;
sc++;
}
if (sc != kNumClasses) {
Log(kCrash, __FILE__, __LINE__,
"wrong number of size classes: (found vs. expected )", sc, kNumClasses);
}
// Initialize the mapping arrays
int next_size = 0;
for (int c = 1; c < kNumClasses; c++) {
const int max_size_in_class = class_to_size_[c];
for (int s = next_size; s <= max_size_in_class; s += kAlignment) {
class_array_[ClassIndex(s)] = c;
}
next_size = max_size_in_class + kAlignment;
}
// Double-check sizes just to be safe
for (size_t size = 0; size <= kMaxSize; size++) {
const int sc = SizeClass(size);
if (sc <= 0 || sc >= kNumClasses) {
Log(kCrash, __FILE__, __LINE__,
"Bad size class (class, size)", sc, size);
}
if (sc > 1 && size <= class_to_size_[sc-1]) {
Log(kCrash, __FILE__, __LINE__,
"Allocating unnecessarily large class (class, size)", sc, size);
}
const size_t s = class_to_size_[sc];
if (size > s || s == 0) {
Log(kCrash, __FILE__, __LINE__,
"Bad (class, size, requested)", sc, s, size);
}
}
// Initialize the num_objects_to_move array.
for (size_t cl = 1; cl < kNumClasses; ++cl) {
num_objects_to_move_[cl] = NumMoveSize(ByteSizeForClass(cl));
}
}
// Metadata allocator -- keeps stats about how many bytes allocated.
static uint64_t metadata_system_bytes_ = 0;
void* MetaDataAlloc(size_t bytes) {
void* result = TCMalloc_SystemAlloc(bytes, NULL);
if (result != NULL) {
metadata_system_bytes_ += bytes;
}
return result;
}
uint64_t metadata_system_bytes() { return metadata_system_bytes_; }
} // namespace tcmalloc