allocator.h

/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef TENSORFLOW_FRAMEWORK_ALLOCATOR_H_
#define TENSORFLOW_FRAMEWORK_ALLOCATOR_H_

#include <stdlib.h>

#include <limits>

#include "tensorflow/core/framework/numeric_types.h"
#include "tensorflow/core/framework/resource_handle.h"
#include "tensorflow/core/framework/type_traits.h"
#include "tensorflow/core/framework/variant.h"
#include "tensorflow/core/platform/logging.h"
#include "tensorflow/core/platform/types.h"

namespace tensorflow {

// Attributes for a single allocation call. Different calls to the same
// allocator could potentially have different allocation attributes.
struct AllocationAttributes {
  // If the first attempt to allocate the memory fails, the allocation
  // should return immediately without retrying.
  // An example use case is optional scratch spaces where a failure
  // has only performance impact.
  bool no_retry_on_failure = false;
  // If a Tensor is allocated without the following set to true, then
  // it is logged as an unknown allocation. During execution Tensors
  // should be allocated through the OpKernelContext which records
  // which Op is performing the allocation, and sets this flag to
  // true.
  bool allocation_will_be_logged = false;
};

// Runtime statistics collected by an allocator.
struct AllocatorStats {
  int64 num_allocs;        // Number of allocations.
  int64 bytes_in_use;      // Number of bytes in use.
  int64 max_bytes_in_use;  // The maximum bytes in use.
  int64 max_alloc_size;    // The max single allocation seen.

  // The upper limit what the allocator can allocate, if such a limit
  // is known. Certain allocator may return 0 to indicate the limit is
  // unknown.
  int64 bytes_limit;

  AllocatorStats() { Clear(); }

  void Clear();
  string DebugString() const;
};

// Allocator is an abstract interface for allocating and deallocating
// device memory.
class Allocator {
 public:
#ifdef EIGEN_VECTORIZE_AVX512
  // Align to 64 byte boundary.
  static constexpr size_t kAllocatorAlignment = 64;
#else
  // Align to 32 byte boundary.
  static constexpr size_t kAllocatorAlignment = 32;
#endif

  virtual ~Allocator();

  // Return a string identifying this allocator
  virtual string Name() = 0;

  // Return an uninitialized block of memory that is "num_bytes" bytes
  // in size.  The returned pointer is guaranteed to be aligned to a
  // multiple of "alignment" bytes.
  // REQUIRES: "alignment" is a power of 2.
  virtual void* AllocateRaw(size_t alignment, size_t num_bytes) = 0;

  // Return an uninitialized block of memory that is "num_bytes" bytes
  // in size with specified allocation attributes.  The returned pointer is
  // guaranteed to be aligned to a multiple of "alignment" bytes.
  // REQUIRES: "alignment" is a power of 2.
  virtual void* AllocateRaw(size_t alignment, size_t num_bytes,
                            const AllocationAttributes& allocation_attr) {
    // The default behavior is to use the implementation without any allocation
    // attributes.
    return AllocateRaw(alignment, num_bytes);
  }

  // Deallocate a block of memory pointer to by "ptr"
  // REQUIRES: "ptr" was previously returned by a call to AllocateRaw
  virtual void DeallocateRaw(void* ptr) = 0;

  // Convenience functions to do typed allocation.  C++ constructors
  // and destructors are invoked for complex types if necessary,
  // depending on the concrete Allocator implementation. May return
  // NULL if the tensor has too many elements to represent in a single
  // allocation.
  template <typename T>
  T* Allocate(size_t num_elements) {
    return Allocate<T>(num_elements, AllocationAttributes());
  }

  template <typename T>
  T* Allocate(size_t num_elements,
              const AllocationAttributes& allocation_attr) {
    // TODO(jeff): Do we need to allow clients to pass in alignment
    // requirements?

    if (num_elements > (std::numeric_limits<size_t>::max() / sizeof(T))) {
      return NULL;
    }

    void* p = AllocateRaw(kAllocatorAlignment, sizeof(T) * num_elements,
                          allocation_attr);
    T* typed_p = reinterpret_cast<T*>(p);
    if (typed_p) RunCtor<T>(typed_p, num_elements);
    return typed_p;
  }

  template <typename T>
  void Deallocate(T* ptr, size_t num_elements) {
    if (ptr) {
      RunDtor<T>(ptr, num_elements);
      DeallocateRaw(ptr);
    }
  }

  // Returns true if this allocator tracks the sizes of allocations.
  // RequestedSize and AllocatedSize must be overridden if
  // TracksAllocationSizes is overridden to return true.
  virtual bool TracksAllocationSizes() { return false; }

  // Returns true if this allocator requires tensors with 0 elements
  // to allocate buffers. This is false for most allocators, but may
  // be used by special-case allocators that want to track tensor
  // usage.
  virtual bool ShouldAllocateEmptyTensors() { return false; }

  // Returns the user-requested size of the data allocated at
  // 'ptr'.  Note that the actual buffer allocated might be larger
  // than requested, but this function returns the size requested by
  // the user.
  //
  // REQUIRES: TracksAllocationSizes() is true.
  //
  // REQUIRES: 'ptr!=nullptr' and points to a buffer previously
  // allocated by this allocator.
  virtual size_t RequestedSize(void* ptr) {
    CHECK(false) << "allocator doesn't track sizes";
    return size_t(0);
  }

  // Returns the allocated size of the buffer at 'ptr' if known,
  // otherwise returns RequestedSize(ptr). AllocatedSize(ptr) is
  // guaranteed to be >= RequestedSize(ptr).
  //
  // REQUIRES: TracksAllocationSizes() is true.
  //
  // REQUIRES: 'ptr!=nullptr' and points to a buffer previously
  // allocated by this allocator.
  virtual size_t AllocatedSize(void* ptr) { return RequestedSize(ptr); }

  // Returns either 0 or an identifier assigned to the buffer at 'ptr'
  // when the buffer was returned by AllocateRaw. If non-zero, the
  // identifier differs from every other ID assigned by this
  // allocator.
  //
  // REQUIRES: TracksAllocationSizes() is true.
  //
  // REQUIRES: 'ptr!=nullptr' and points to a buffer previously
  // allocated by this allocator.
  virtual int64 AllocationId(void* ptr) { return 0; }

  // Returns the allocated size of the buffer at 'ptr' if known,
  // otherwise returns 0. This method can be called when
  // TracksAllocationSizes() is false, but can be extremely slow.
  //
  // REQUIRES: 'ptr!=nullptr' and points to a buffer previously
  // allocated by this allocator.
  virtual size_t AllocatedSizeSlow(void* ptr) {
    if (TracksAllocationSizes()) {
      return AllocatedSize(ptr);
    }
    return 0;
  }

  // Fills in 'stats' with statistics collected by this allocator.
  virtual void GetStats(AllocatorStats* stats) { stats->Clear(); }

 private:
  // No constructors or destructors are run for simple types
  template <typename T>
  void RunCtor(T* p, size_t n) {
    static_assert(is_simple_type<T>::value, "T is not a simple type.");
  }

  template <typename T>
  void RunDtor(T* p, size_t n) {}

  // custom constructors and destructors that can be overridden for
  // non-standard allocators

  // Runs string's default constructor for  p[0], p[1], ..., p[n-1].
  virtual void RunStringCtor(string* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) new (p) string();
  }

  // Runs string's default destructor for  p[0], p[1], ..., p[n-1].
  virtual void RunStringDtor(string* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) p->~string();
  }

  virtual void RunResourceCtor(ResourceHandle* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) new (p) ResourceHandle();
  }

  // Runs string's default destructor for  p[0], p[1], ..., p[n-1].
  virtual void RunResourceDtor(ResourceHandle* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) p->~ResourceHandle();
  }

  virtual void RunVariantCtor(Variant* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) new (p) Variant();
  }

  virtual void RunVariantDtor(Variant* p, size_t n) {
    for (size_t i = 0; i < n; ++p, ++i) p->~Variant();
  }

  // TODO(jeff): Maybe provide some interface to give info about
  // current allocation state (total number of bytes available for
  // allocation, number of bytes free on device, etc.)
};

// Allocator-specific constructors and destructors are used for
// strings
template <>
inline void Allocator::RunCtor(string* p, size_t n) {
  RunStringCtor(p, n);
}

template <>
inline void Allocator::RunDtor(string* p, size_t n) {
  RunStringDtor(p, n);
}

template <>
inline void Allocator::RunCtor(ResourceHandle* p, size_t n) {
  RunResourceCtor(p, n);
}

template <>
inline void Allocator::RunDtor(ResourceHandle* p, size_t n) {
  RunResourceDtor(p, n);
}

template <>
inline void Allocator::RunCtor(Variant* p, size_t n) {
  RunVariantCtor(p, n);
}

template <>
inline void Allocator::RunDtor(Variant* p, size_t n) {
  RunVariantDtor(p, n);
}

// An implementation of Allocator that delegates all calls to another Allocator.
//
// Useful to clients who want to override part of the functionality of another
// allocator.
class AllocatorWrapper : public Allocator {
 public:
  explicit AllocatorWrapper(Allocator* wrapped) : wrapped_(wrapped) {}

  ~AllocatorWrapper() override {}

  // Returns the wrapped allocator to which all calls are delegated.
  Allocator* wrapped() const { return wrapped_; }

  string Name() override { return wrapped_->Name(); }

  void* AllocateRaw(size_t alignment, size_t num_bytes) override {
    return wrapped_->AllocateRaw(alignment, num_bytes);
  }

  void* AllocateRaw(size_t alignment, size_t num_bytes,
                    const AllocationAttributes& allocation_attr) override {
    return wrapped_->AllocateRaw(alignment, num_bytes, allocation_attr);
  }

  void DeallocateRaw(void* ptr) override { wrapped_->DeallocateRaw(ptr); }

  bool TracksAllocationSizes() override {
    return wrapped_->TracksAllocationSizes();
  }

  bool ShouldAllocateEmptyTensors() override {
    return wrapped_->TracksAllocationSizes();
  }

  size_t RequestedSize(void* ptr) override {
    return wrapped_->RequestedSize(ptr);
  }

  size_t AllocatedSize(void* ptr) override {
    return wrapped_->AllocatedSize(ptr);
  }

  int64 AllocationId(void* ptr) override { return wrapped_->AllocationId(ptr); }

  size_t AllocatedSizeSlow(void* ptr) override {
    return wrapped_->AllocatedSizeSlow(ptr);
  }

 private:
  Allocator* const wrapped_;
};

// A tensorflow Op may need access to different kinds of memory that
// are not simply a function of the device to which the Op has been
// assigned.  For example, an Op executing on a GPU may still need
// to allocate CPU RAM for some purpose.  Internal to the tensorflow
// runtime we may choose to allocate CPU ram from special regions
// that have been prepared for higher performance in some use
// contexts, e.g. doing DMA with particular devices.  For these
// reasons, the Device interface does not expose just one memory
// Allocator, but instead provides an accessor that takes a
// specification of the desired memory attributes in order to select
// an Allocator.
//
// Example use:
//  // Allocator for ordinary device memory:
//  Allocator* a = allocator(AllocatorAttributes());
// ...
//  // Allocator for CPU RAM, regardless of where Op is executing:
//  AllocatorAttributes attr;
//  attr.set_on_host(true);
//  Allocator* a = allocator(attr);
struct AllocatorAttributes {
  void set_on_host(bool v) { value |= (static_cast<int>(v)); }
  bool on_host() const { return value & 0x1; }
  void set_nic_compatible(bool v) { value |= (static_cast<int>(v) << 1); }
  bool nic_compatible() const { return value & (0x1 << 1); }
  void set_gpu_compatible(bool v) { value |= (static_cast<int>(v) << 2); }
  bool gpu_compatible() const { return value & (0x1 << 2); }
  void Merge(AllocatorAttributes other) { value |= other.value; }
  // Returns true if the fields set in *this is a subset of or equal to
  // those set in other.
  bool IsEqualOrLessRestrictiveThan(const AllocatorAttributes& other) const {
    return (value | other.value) == other.value;
  }

  // NOTE: The upper 8 bits of the value are reserved for
  // device-specific uses.  Implementors of a device can interpret these
  // upper 8 bits in device-specific ways, and ops implemented for those
  // devices are responsible for setting those 8 bits appropriately.
  uint32 value = 0;
};

// Returns a trivial implementation of Allocator which uses the system
// default malloc. The returned allocator is a process singleton.
Allocator* cpu_allocator();

// If 'enable' is true, the process-wide cpu allocator collects
// AllocatorStats. By default, it's disabled.
void EnableCPUAllocatorStats(bool enable);

// If 'enable' is true, the process-wide cpu allocator collects full
// statistics. By default, it's disabled.
void EnableCPUAllocatorFullStats(bool enable);

// Abstract interface of an object that does the underlying suballoc/free of
// memory for a higher-level allocator.
class SubAllocator {
 public:
  virtual ~SubAllocator() {}
  virtual void* Alloc(size_t alignment, size_t num_bytes) = 0;
  virtual void Free(void* ptr, size_t num_bytes) = 0;
};

}  // namespace tensorflow

#endif  // TENSORFLOW_FRAMEWORK_ALLOCATOR_H_