Revert of Use DiscardableMemoryManager on Android.

base/memory/discardable_memory_allocator_android.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/memory/discardable_memory_allocator_android.h"
+
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+#include <set>
+#include <utility>
+
+#include "base/basictypes.h"
+#include "base/containers/hash_tables.h"
+#include "base/file_util.h"
+#include "base/files/scoped_file.h"
+#include "base/logging.h"
+#include "base/memory/discardable_memory.h"
+#include "base/memory/scoped_vector.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+#include "third_party/ashmem/ashmem.h"
+
+// The allocator consists of three parts (classes):
+// - DiscardableMemoryAllocator: entry point of all allocations (through its
+// Allocate() method) that are dispatched to the AshmemRegion instances (which
+// it owns).
+// - AshmemRegion: manages allocations and destructions inside a single large
+// (e.g. 32 MBytes) ashmem region.
+// - DiscardableAshmemChunk: class implementing the DiscardableMemory interface
+// whose instances are returned to the client. DiscardableAshmemChunk lets the
+// client seamlessly operate on a subrange of the ashmem region managed by
+// AshmemRegion.
+
+namespace base {
+namespace {
+
+// Only tolerate fragmentation in used chunks *caused by the client* (as opposed
+// to the allocator when a free chunk is reused). The client can cause such
+// fragmentation by e.g. requesting 4097 bytes. This size would be rounded up to
+// 8192 by the allocator which would cause 4095 bytes of fragmentation (which is
+// currently the maximum allowed). If the client requests 4096 bytes and a free
+// chunk of 8192 bytes is available then the free chunk gets splitted into two
+// pieces to minimize fragmentation (since 8192 - 4096 = 4096 which is greater
+// than 4095).
+// TODO(pliard): tune this if splitting chunks too often leads to performance
+// issues.
+const size_t kMaxChunkFragmentationBytes = 4096 - 1;
+
+const size_t kMinAshmemRegionSize = 32 * 1024 * 1024;
+
+// Returns 0 if the provided size is too high to be aligned.
+size_t AlignToNextPage(size_t size) {
+  const size_t kPageSize = 4096;
+  DCHECK_EQ(static_cast<int>(kPageSize), getpagesize());
+  if (size > std::numeric_limits<size_t>::max() - kPageSize + 1)
+    return 0;
+  const size_t mask = ~(kPageSize - 1);
+  return (size + kPageSize - 1) & mask;
+}
+
+bool CreateAshmemRegion(const char* name,
+                        size_t size,
+                        int* out_fd,
+                        void** out_address) {
+  base::ScopedFD fd(ashmem_create_region(name, size));
+  if (!fd.is_valid()) {
+    DLOG(ERROR) << "ashmem_create_region() failed";
+    return false;
+  }
+
+  const int err = ashmem_set_prot_region(fd.get(), PROT_READ | PROT_WRITE);
+  if (err < 0) {
+    DLOG(ERROR) << "Error " << err << " when setting protection of ashmem";
+    return false;
+  }
+
+  // There is a problem using MAP_PRIVATE here. As we are constantly calling
+  // Lock() and Unlock(), data could get lost if they are not written to the
+  // underlying file when Unlock() gets called.
+  void* const address = mmap(
+      NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd.get(), 0);
+  if (address == MAP_FAILED) {
+    DPLOG(ERROR) << "Failed to map memory.";
+    return false;
+  }
+
+  *out_fd = fd.release();
+  *out_address = address;
+  return true;
+}
+
+bool CloseAshmemRegion(int fd, size_t size, void* address) {
+  if (munmap(address, size) == -1) {
+    DPLOG(ERROR) << "Failed to unmap memory.";
+    close(fd);
+    return false;
+  }
+  return close(fd) == 0;
+}
+
+DiscardableMemoryLockStatus LockAshmemRegion(int fd, size_t off, size_t size) {
+  const int result = ashmem_pin_region(fd, off, size);
+  return result == ASHMEM_WAS_PURGED ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
+                                     : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
+}
+
+bool UnlockAshmemRegion(int fd, size_t off, size_t size) {
+  const int failed = ashmem_unpin_region(fd, off, size);
+  if (failed)
+    DLOG(ERROR) << "Failed to unpin memory.";
+  return !failed;
+}
+
+}  // namespace
+
+namespace internal {
+
+class DiscardableMemoryAllocator::DiscardableAshmemChunk
+    : public DiscardableMemory {
+ public:
+  // Note that |ashmem_region| must outlive |this|.
+  DiscardableAshmemChunk(AshmemRegion* ashmem_region,
+                         int fd,
+                         void* address,
+                         size_t offset,
+                         size_t size)
+      : ashmem_region_(ashmem_region),
+        fd_(fd),
+        address_(address),
+        offset_(offset),
+        size_(size),
+        locked_(true) {
+  }
+
+  // Implemented below AshmemRegion since this requires the full definition of
+  // AshmemRegion.
+  virtual ~DiscardableAshmemChunk();
+
+  // DiscardableMemory:
+  virtual DiscardableMemoryLockStatus Lock() OVERRIDE {
+    DCHECK(!locked_);
+    locked_ = true;
+    return LockAshmemRegion(fd_, offset_, size_);
+  }
+
+  virtual void Unlock() OVERRIDE {
+    DCHECK(locked_);
+    locked_ = false;
+    UnlockAshmemRegion(fd_, offset_, size_);
+  }
+
+  virtual void* Memory() const OVERRIDE {
+    return address_;
+  }
+
+ private:
+  AshmemRegion* const ashmem_region_;
+  const int fd_;
+  void* const address_;
+  const size_t offset_;
+  const size_t size_;
+  bool locked_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableAshmemChunk);
+};
+
+class DiscardableMemoryAllocator::AshmemRegion {
+ public:
+  // Note that |allocator| must outlive |this|.
+  static scoped_ptr<AshmemRegion> Create(
+      size_t size,
+      const std::string& name,
+      DiscardableMemoryAllocator* allocator) {
+    DCHECK_EQ(size, AlignToNextPage(size));
+    int fd;
+    void* base;
+    if (!CreateAshmemRegion(name.c_str(), size, &fd, &base))
+      return scoped_ptr<AshmemRegion>();
+    return make_scoped_ptr(new AshmemRegion(fd, size, base, allocator));
+  }
+
+  ~AshmemRegion() {
+    const bool result = CloseAshmemRegion(fd_, size_, base_);
+    DCHECK(result);
+    DCHECK(!highest_allocated_chunk_);
+  }
+
+  // Returns a new instance of DiscardableMemory whose size is greater or equal
+  // than |actual_size| (which is expected to be greater or equal than
+  // |client_requested_size|).
+  // Allocation works as follows:
+  // 1) Reuse a previously freed chunk and return it if it succeeded. See
+  // ReuseFreeChunk_Locked() below for more information.
+  // 2) If no free chunk could be reused and the region is not big enough for
+  // the requested size then NULL is returned.
+  // 3) If there is enough room in the ashmem region then a new chunk is
+  // returned. This new chunk starts at |offset_| which is the end of the
+  // previously highest chunk in the region.
+  scoped_ptr<DiscardableMemory> Allocate_Locked(size_t client_requested_size,
+                                                size_t actual_size) {
+    DCHECK_LE(client_requested_size, actual_size);
+    allocator_->lock_.AssertAcquired();
+
+    // Check that the |highest_allocated_chunk_| field doesn't contain a stale
+    // pointer. It should point to either a free chunk or a used chunk.
+    DCHECK(!highest_allocated_chunk_ ||
+           address_to_free_chunk_map_.find(highest_allocated_chunk_) !=
+               address_to_free_chunk_map_.end() ||
+           used_to_previous_chunk_map_.find(highest_allocated_chunk_) !=
+               used_to_previous_chunk_map_.end());
+
+    scoped_ptr<DiscardableMemory> memory = ReuseFreeChunk_Locked(
+        client_requested_size, actual_size);
+    if (memory)
+      return memory.Pass();
+
+    if (size_ - offset_ < actual_size) {
+      // This region does not have enough space left to hold the requested size.
+      return scoped_ptr<DiscardableMemory>();
+    }
+
+    void* const address = static_cast<char*>(base_) + offset_;
+    memory.reset(
+        new DiscardableAshmemChunk(this, fd_, address, offset_, actual_size));
+
+    used_to_previous_chunk_map_.insert(
+        std::make_pair(address, highest_allocated_chunk_));
+    highest_allocated_chunk_ = address;
+    offset_ += actual_size;
+    DCHECK_LE(offset_, size_);
+    return memory.Pass();
+  }
+
+  void OnChunkDeletion(void* chunk, size_t size) {
+    AutoLock auto_lock(allocator_->lock_);
+    MergeAndAddFreeChunk_Locked(chunk, size);
+    // Note that |this| might be deleted beyond this point.
+  }
+
+ private:
+  struct FreeChunk {
+    FreeChunk() : previous_chunk(NULL), start(NULL), size(0) {}
+
+    explicit FreeChunk(size_t size)
+        : previous_chunk(NULL),
+          start(NULL),
+          size(size) {
+    }
+
+    FreeChunk(void* previous_chunk, void* start, size_t size)
+        : previous_chunk(previous_chunk),
+          start(start),
+          size(size) {
+      DCHECK_LT(previous_chunk, start);
+    }
+
+    void* const previous_chunk;
+    void* const start;
+    const size_t size;
+
+    bool is_null() const { return !start; }
+
+    bool operator<(const FreeChunk& other) const {
+      return size < other.size;
+    }
+  };
+
+  // Note that |allocator| must outlive |this|.
+  AshmemRegion(int fd,
+               size_t size,
+               void* base,
+               DiscardableMemoryAllocator* allocator)
+      : fd_(fd),
+        size_(size),
+        base_(base),
+        allocator_(allocator),
+        highest_allocated_chunk_(NULL),
+        offset_(0) {
+    DCHECK_GE(fd_, 0);
+    DCHECK_GE(size, kMinAshmemRegionSize);
+    DCHECK(base);
+    DCHECK(allocator);
+  }
+
+  // Tries to reuse a previously freed chunk by doing a closest size match.
+  scoped_ptr<DiscardableMemory> ReuseFreeChunk_Locked(
+      size_t client_requested_size,
+      size_t actual_size) {
+    allocator_->lock_.AssertAcquired();
+    const FreeChunk reused_chunk = RemoveFreeChunkFromIterator_Locked(
+        free_chunks_.lower_bound(FreeChunk(actual_size)));
+    if (reused_chunk.is_null())
+      return scoped_ptr<DiscardableMemory>();
+
+    used_to_previous_chunk_map_.insert(
+        std::make_pair(reused_chunk.start, reused_chunk.previous_chunk));
+    size_t reused_chunk_size = reused_chunk.size;
+    // |client_requested_size| is used below rather than |actual_size| to
+    // reflect the amount of bytes that would not be usable by the client (i.e.
+    // wasted). Using |actual_size| instead would not allow us to detect
+    // fragmentation caused by the client if he did misaligned allocations.
+    DCHECK_GE(reused_chunk.size, client_requested_size);
+    const size_t fragmentation_bytes =
+        reused_chunk.size - client_requested_size;
+
+    if (fragmentation_bytes > kMaxChunkFragmentationBytes) {
+      // Split the free chunk being recycled so that its unused tail doesn't get
+      // reused (i.e. locked) which would prevent it from being evicted under
+      // memory pressure.
+      reused_chunk_size = actual_size;
+      void* const new_chunk_start =
+          static_cast<char*>(reused_chunk.start) + actual_size;
+      if (reused_chunk.start == highest_allocated_chunk_) {
+        // We also need to update the pointer to the highest allocated chunk in
+        // case we are splitting the highest chunk.
+        highest_allocated_chunk_ = new_chunk_start;
+      }
+      DCHECK_GT(reused_chunk.size, actual_size);
+      const size_t new_chunk_size = reused_chunk.size - actual_size;
+      // Note that merging is not needed here since there can't be contiguous
+      // free chunks at this point.
+      AddFreeChunk_Locked(
+          FreeChunk(reused_chunk.start, new_chunk_start, new_chunk_size));
+    }
+
+    const size_t offset =
+        static_cast<char*>(reused_chunk.start) - static_cast<char*>(base_);
+    LockAshmemRegion(fd_, offset, reused_chunk_size);
+    scoped_ptr<DiscardableMemory> memory(
+        new DiscardableAshmemChunk(this, fd_, reused_chunk.start, offset,
+                                   reused_chunk_size));
+    return memory.Pass();
+  }
+
+  // Makes the chunk identified with the provided arguments free and possibly
+  // merges this chunk with the previous and next contiguous ones.
+  // If the provided chunk is the only one used (and going to be freed) in the
+  // region then the internal ashmem region is closed so that the underlying
+  // physical pages are immediately released.
+  // Note that free chunks are unlocked therefore they can be reclaimed by the
+  // kernel if needed (under memory pressure) but they are not immediately
+  // released unfortunately since madvise(MADV_REMOVE) and
+  // fallocate(FALLOC_FL_PUNCH_HOLE) don't seem to work on ashmem. This might
+  // change in versions of kernel >=3.5 though. The fact that free chunks are
+  // not immediately released is the reason why we are trying to minimize
+  // fragmentation in order not to cause "artificial" memory pressure.
+  void MergeAndAddFreeChunk_Locked(void* chunk, size_t size) {
+    allocator_->lock_.AssertAcquired();
+    size_t new_free_chunk_size = size;
+    // Merge with the previous chunk.
+    void* first_free_chunk = chunk;
+    DCHECK(!used_to_previous_chunk_map_.empty());
+    const hash_map<void*, void*>::iterator previous_chunk_it =
+        used_to_previous_chunk_map_.find(chunk);
+    DCHECK(previous_chunk_it != used_to_previous_chunk_map_.end());
+    void* previous_chunk = previous_chunk_it->second;
+    used_to_previous_chunk_map_.erase(previous_chunk_it);
+
+    if (previous_chunk) {
+      const FreeChunk free_chunk = RemoveFreeChunk_Locked(previous_chunk);
+      if (!free_chunk.is_null()) {
+        new_free_chunk_size += free_chunk.size;
+        first_free_chunk = previous_chunk;
+        if (chunk == highest_allocated_chunk_)
+          highest_allocated_chunk_ = previous_chunk;
+
+        // There should not be more contiguous previous free chunks.
+        previous_chunk = free_chunk.previous_chunk;
+        DCHECK(!address_to_free_chunk_map_.count(previous_chunk));
+      }
+    }
+
+    // Merge with the next chunk if free and present.
+    void* next_chunk = static_cast<char*>(chunk) + size;
+    const FreeChunk next_free_chunk = RemoveFreeChunk_Locked(next_chunk);
+    if (!next_free_chunk.is_null()) {
+      new_free_chunk_size += next_free_chunk.size;
+      if (next_free_chunk.start == highest_allocated_chunk_)
+        highest_allocated_chunk_ = first_free_chunk;
+
+      // Same as above.
+      DCHECK(!address_to_free_chunk_map_.count(static_cast<char*>(next_chunk) +
+                                               next_free_chunk.size));
+    }
+
+    const bool whole_ashmem_region_is_free =
+        used_to_previous_chunk_map_.empty();
+    if (!whole_ashmem_region_is_free) {
+      AddFreeChunk_Locked(
+          FreeChunk(previous_chunk, first_free_chunk, new_free_chunk_size));
+      return;
+    }
+
+    // The whole ashmem region is free thus it can be deleted.
+    DCHECK_EQ(base_, first_free_chunk);
+    DCHECK_EQ(base_, highest_allocated_chunk_);
+    DCHECK(free_chunks_.empty());
+    DCHECK(address_to_free_chunk_map_.empty());
+    DCHECK(used_to_previous_chunk_map_.empty());
+    highest_allocated_chunk_ = NULL;
+    allocator_->DeleteAshmemRegion_Locked(this);  // Deletes |this|.
+  }
+
+  void AddFreeChunk_Locked(const FreeChunk& free_chunk) {
+    allocator_->lock_.AssertAcquired();
+    const std::multiset<FreeChunk>::iterator it = free_chunks_.insert(
+        free_chunk);
+    address_to_free_chunk_map_.insert(std::make_pair(free_chunk.start, it));
+    // Update the next used contiguous chunk, if any, since its previous chunk
+    // may have changed due to free chunks merging/splitting.
+    void* const next_used_contiguous_chunk =
+        static_cast<char*>(free_chunk.start) + free_chunk.size;
+    hash_map<void*, void*>::iterator previous_it =
+        used_to_previous_chunk_map_.find(next_used_contiguous_chunk);
+    if (previous_it != used_to_previous_chunk_map_.end())
+      previous_it->second = free_chunk.start;
+  }
+
+  // Finds and removes the free chunk, if any, whose start address is
+  // |chunk_start|. Returns a copy of the unlinked free chunk or a free chunk
+  // whose content is null if it was not found.
+  FreeChunk RemoveFreeChunk_Locked(void* chunk_start) {
+    allocator_->lock_.AssertAcquired();
+    const hash_map<
+        void*, std::multiset<FreeChunk>::iterator>::iterator it =
+            address_to_free_chunk_map_.find(chunk_start);
+    if (it == address_to_free_chunk_map_.end())
+      return FreeChunk();
+    return RemoveFreeChunkFromIterator_Locked(it->second);
+  }
+
+  // Same as above but takes an iterator in.
+  FreeChunk RemoveFreeChunkFromIterator_Locked(
+      std::multiset<FreeChunk>::iterator free_chunk_it) {
+    allocator_->lock_.AssertAcquired();
+    if (free_chunk_it == free_chunks_.end())
+      return FreeChunk();
+    DCHECK(free_chunk_it != free_chunks_.end());
+    const FreeChunk free_chunk(*free_chunk_it);
+    address_to_free_chunk_map_.erase(free_chunk_it->start);
+    free_chunks_.erase(free_chunk_it);
+    return free_chunk;
+  }
+
+  const int fd_;
+  const size_t size_;
+  void* const base_;
+  DiscardableMemoryAllocator* const allocator_;
+  // Points to the chunk with the highest address in the region. This pointer
+  // needs to be carefully updated when chunks are merged/split.
+  void* highest_allocated_chunk_;
+  // Points to the end of |highest_allocated_chunk_|.
+  size_t offset_;
+  // Allows free chunks recycling (lookup, insertion and removal) in O(log N).
+  // Note that FreeChunk values are indexed by their size and also note that
+  // multiple free chunks can have the same size (which is why multiset<> is
+  // used instead of e.g. set<>).
+  std::multiset<FreeChunk> free_chunks_;
+  // Used while merging free contiguous chunks to erase free chunks (from their
+  // start address) in constant time. Note that multiset<>::{insert,erase}()
+  // don't invalidate iterators (except the one for the element being removed
+  // obviously).
+  hash_map<
+      void*, std::multiset<FreeChunk>::iterator> address_to_free_chunk_map_;
+  // Maps the address of *used* chunks to the address of their previous
+  // contiguous chunk.
+  hash_map<void*, void*> used_to_previous_chunk_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(AshmemRegion);
+};
+
+DiscardableMemoryAllocator::DiscardableAshmemChunk::~DiscardableAshmemChunk() {
+  if (locked_)
+    UnlockAshmemRegion(fd_, offset_, size_);
+  ashmem_region_->OnChunkDeletion(address_, size_);
+}
+
+DiscardableMemoryAllocator::DiscardableMemoryAllocator(
+    const std::string& name,
+    size_t ashmem_region_size)
+    : name_(name),
+      ashmem_region_size_(
+          std::max(kMinAshmemRegionSize, AlignToNextPage(ashmem_region_size))),
+      last_ashmem_region_size_(0) {
+  DCHECK_GE(ashmem_region_size_, kMinAshmemRegionSize);
+}
+
+DiscardableMemoryAllocator::~DiscardableMemoryAllocator() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(ashmem_regions_.empty());
+}
+
+scoped_ptr<DiscardableMemory> DiscardableMemoryAllocator::Allocate(
+    size_t size) {
+  const size_t aligned_size = AlignToNextPage(size);
+  if (!aligned_size)
+    return scoped_ptr<DiscardableMemory>();
+  // TODO(pliard): make this function less naive by e.g. moving the free chunks
+  // multiset to the allocator itself in order to decrease even more
+  // fragmentation/speedup allocation. Note that there should not be more than a
+  // couple (=5) of AshmemRegion instances in practice though.
+  AutoLock auto_lock(lock_);
+  DCHECK_LE(ashmem_regions_.size(), 5U);
+  for (ScopedVector<AshmemRegion>::iterator it = ashmem_regions_.begin();
+       it != ashmem_regions_.end(); ++it) {
+    scoped_ptr<DiscardableMemory> memory(
+        (*it)->Allocate_Locked(size, aligned_size));
+    if (memory)
+      return memory.Pass();
+  }
+  // The creation of the (large) ashmem region might fail if the address space
+  // is too fragmented. In case creation fails the allocator retries by
+  // repetitively dividing the size by 2.
+  const size_t min_region_size = std::max(kMinAshmemRegionSize, aligned_size);
+  for (size_t region_size = std::max(ashmem_region_size_, aligned_size);
+       region_size >= min_region_size;
+       region_size = AlignToNextPage(region_size / 2)) {
+    scoped_ptr<AshmemRegion> new_region(
+        AshmemRegion::Create(region_size, name_.c_str(), this));
+    if (!new_region)
+      continue;
+    last_ashmem_region_size_ = region_size;
+    ashmem_regions_.push_back(new_region.release());
+    return ashmem_regions_.back()->Allocate_Locked(size, aligned_size);
+  }
+  // TODO(pliard): consider adding an histogram to see how often this happens.
+  return scoped_ptr<DiscardableMemory>();
+}
+
+size_t DiscardableMemoryAllocator::last_ashmem_region_size() const {
+  AutoLock auto_lock(lock_);
+  return last_ashmem_region_size_;
+}
+
+void DiscardableMemoryAllocator::DeleteAshmemRegion_Locked(
+    AshmemRegion* region) {
+  lock_.AssertAcquired();
+  // Note that there should not be more than a couple of ashmem region instances
+  // in |ashmem_regions_|.
+  DCHECK_LE(ashmem_regions_.size(), 5U);
+  const ScopedVector<AshmemRegion>::iterator it = std::find(
+      ashmem_regions_.begin(), ashmem_regions_.end(), region);
+  DCHECK_NE(ashmem_regions_.end(), it);
+  std::swap(*it, ashmem_regions_.back());
+  ashmem_regions_.pop_back();
+}
+
+}  // namespace internal
+}  // namespace base