// 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>
//
// Common definitions for tcmalloc code.
#ifndef TCMALLOC_COMMON_H_
#define TCMALLOC_COMMON_H_
#include "config.h"
#include <stddef.h> // for size_t
#ifdef HAVE_STDINT_H
#include <stdint.h> // for uintptr_t, uint64_t
#endif
#include "free_list.h" // for SIZE_CLASS macros
#include "internal_logging.h" // for ASSERT, etc
// Type that can hold a page number
typedef uintptr_t PageID;
// Type that can hold the length of a run of pages
typedef uintptr_t Length;
//-------------------------------------------------------------------
// Configuration
//-------------------------------------------------------------------
// Using large pages speeds up the execution at a cost of larger memory use.
// Deallocation may speed up by a factor as the page map gets 8x smaller, so
// lookups in the page map result in fewer L2 cache misses, which translates to
// speedup for application/platform combinations with high L2 cache pressure.
// As the number of size classes increases with large pages, we increase
// the thread cache allowance to avoid passing more free ranges to and from
// central lists. Also, larger pages are less likely to get freed.
// These two factors cause a bounded increase in memory use.
static const size_t kAlignment = 8;
// Constants dependant on tcmalloc configuration and archetecture. Chromium
// tunes these constants.
// We need to guarantee the smallest class size is big enough to hold the
// pointers that form the free list.
static const size_t kNumFreeListPointers =
(tcmalloc::kSupportsDoublyLinkedList ? 2 : 1);
static const size_t kLinkSize = kNumFreeListPointers * sizeof(void *);
static const size_t kMinClassSize =
(kLinkSize > kAlignment ? kLinkSize : kAlignment);
static const size_t kSkippedClasses = (kAlignment < kMinClassSize ? 1 : 0);
#if defined(TCMALLOC_LARGE_PAGES)
static const size_t kPageShift = 15;
static const size_t kNumClasses = 78 - kSkippedClasses;
#else
// Original TCMalloc code used kPageShift == 13. In Chromium, we changed
// this to 12 (as was done in prior versions of TCMalloc).
static const size_t kPageShift = 12;
static const size_t kNumClasses = 54 - kSkippedClasses;
#endif
static const size_t kMaxThreadCacheSize = 4 << 20;
static const size_t kPageSize = 1 << kPageShift;
// Original TCMalloc code used kMaxSize == 256 * 1024. In Chromium, we
// changed this to 32K, and represent it in terms of page size (as was done
// in prior versions of TCMalloc).
static const size_t kMaxSize = 8u * kPageSize;
// For all span-lengths < kMaxPages we keep an exact-size list.
static const size_t kMaxPages = 1 << (20 - kPageShift);
// Default bound on the total amount of thread caches.
#ifdef TCMALLOC_SMALL_BUT_SLOW
// Make the overall thread cache no bigger than that of a single thread
// for the small memory footprint case.
static const size_t kDefaultOverallThreadCacheSize = kMaxThreadCacheSize;
#else
static const size_t kDefaultOverallThreadCacheSize = 8u * kMaxThreadCacheSize;
#endif
// Lower bound on the per-thread cache sizes
static const size_t kMinThreadCacheSize = kMaxSize * 2;
// The number of bytes one ThreadCache will steal from another when
// the first ThreadCache is forced to Scavenge(), delaying the
// next call to Scavenge for this thread.
static const size_t kStealAmount = 1 << 16;
// The number of times that a deallocation can cause a freelist to
// go over its max_length() before shrinking max_length().
static const int kMaxOverages = 3;
// Maximum length we allow a per-thread free-list to have before we
// move objects from it into the corresponding central free-list. We
// want this big to avoid locking the central free-list too often. It
// should not hurt to make this list somewhat big because the
// scavenging code will shrink it down when its contents are not in use.
static const int kMaxDynamicFreeListLength = 8192;
static const Length kMaxValidPages = (~static_cast<Length>(0)) >> kPageShift;
#if defined __x86_64__
// All current and planned x86_64 processors only look at the lower 48 bits
// in virtual to physical address translation. The top 16 are thus unused.
// TODO(rus): Under what operating systems can we increase it safely to 17?
// This lets us use smaller page maps. On first allocation, a 36-bit page map
// uses only 96 KB instead of the 4.5 MB used by a 52-bit page map.
static const int kAddressBits = (sizeof(void*) < 8 ? (8 * sizeof(void*)) : 48);
#else
static const int kAddressBits = 8 * sizeof(void*);
#endif
namespace tcmalloc {
// Convert byte size into pages. This won't overflow, but may return
// an unreasonably large value if bytes is huge enough.
inline Length pages(size_t bytes) {
return (bytes >> kPageShift) +
((bytes & (kPageSize - 1)) > 0 ? 1 : 0);
}
// For larger allocation sizes, we use larger memory alignments to
// reduce the number of size classes.
int AlignmentForSize(size_t size);
// Size-class information + mapping
class SizeMap {
private:
// Number of objects to move between a per-thread list and a central
// list in one shot. We want this to be not too small so we can
// amortize the lock overhead for accessing the central list. Making
// it too big may temporarily cause unnecessary memory wastage in the
// per-thread free list until the scavenger cleans up the list.
int num_objects_to_move_[kNumClasses];
//-------------------------------------------------------------------
// Mapping from size to size_class and vice versa
//-------------------------------------------------------------------
// Sizes <= 1024 have an alignment >= 8. So for such sizes we have an
// array indexed by ceil(size/8). Sizes > 1024 have an alignment >= 128.
// So for these larger sizes we have an array indexed by ceil(size/128).
//
// We flatten both logical arrays into one physical array and use
// arithmetic to compute an appropriate index. The constants used by
// ClassIndex() were selected to make the flattening work.
//
// Examples:
// Size Expression Index
// -------------------------------------------------------
// 0 (0 + 7) / 8 0
// 1 (1 + 7) / 8 1
// ...
// 1024 (1024 + 7) / 8 128
// 1025 (1025 + 127 + (120<<7)) / 128 129
// ...
// 32768 (32768 + 127 + (120<<7)) / 128 376
static const int kMaxSmallSize = 1024;
static const size_t kClassArraySize =
((kMaxSize + 127 + (120 << 7)) >> 7) + 1;
unsigned char class_array_[kClassArraySize];
// Compute index of the class_array[] entry for a given size
static inline int ClassIndex(int s) {
ASSERT(0 <= s);
ASSERT(s <= kMaxSize);
const bool big = (s > kMaxSmallSize);
const int add_amount = big ? (127 + (120<<7)) : 7;
const int shift_amount = big ? 7 : 3;
return (s + add_amount) >> shift_amount;
}
int NumMoveSize(size_t size);
// Mapping from size class to max size storable in that class
size_t class_to_size_[kNumClasses];
// Mapping from size class to number of pages to allocate at a time
size_t class_to_pages_[kNumClasses];
public:
// Constructor should do nothing since we rely on explicit Init()
// call, which may or may not be called before the constructor runs.
SizeMap() { }
// Initialize the mapping arrays
void Init();
inline int SizeClass(int size) {
return class_array_[ClassIndex(size)];
}
// Get the byte-size for a specified class
inline size_t ByteSizeForClass(size_t cl) {
return class_to_size_[cl];
}
// Mapping from size class to max size storable in that class
inline size_t class_to_size(size_t cl) {
return class_to_size_[cl];
}
// Mapping from size class to number of pages to allocate at a time
inline size_t class_to_pages(size_t cl) {
return class_to_pages_[cl];
}
// Number of objects to move between a per-thread list and a central
// list in one shot. We want this to be not too small so we can
// amortize the lock overhead for accessing the central list. Making
// it too big may temporarily cause unnecessary memory wastage in the
// per-thread free list until the scavenger cleans up the list.
inline int num_objects_to_move(size_t cl) {
return num_objects_to_move_[cl];
}
};
// Allocates "bytes" worth of memory and returns it. Increments
// metadata_system_bytes appropriately. May return NULL if allocation
// fails. Requires pageheap_lock is held.
void* MetaDataAlloc(size_t bytes);
// Returns the total number of bytes allocated from the system.
// Requires pageheap_lock is held.
uint64_t metadata_system_bytes();
uint64_t metadata_unmapped_bytes();
// Adjust metadata_system_bytes to indicate that bytes are actually committed.
// Requires pageheap_lock is held.
void update_metadata_system_bytes(int diff);
void update_metadata_unmapped_bytes(int diff);
// size/depth are made the same size as a pointer so that some generic
// code below can conveniently cast them back and forth to void*.
static const int kMaxStackDepth = 31;
struct StackTrace {
uintptr_t size; // Size of object
uintptr_t depth; // Number of PC values stored in array below
void* stack[kMaxStackDepth];
};
} // namespace tcmalloc
#endif // TCMALLOC_COMMON_H_