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| 1 // Copyright 2013 The Chromium Authors. All rights reserved. | |
| 2 // Use of this source code is governed by a BSD-style license that can be | |
| 3 // found in the LICENSE file. | |
| 4 | |
| 5 #include "base/memory/discardable_memory_allocator_android.h" | |
| 6 | |
| 7 #include <algorithm> | |
| 8 #include <cmath> | |
| 9 #include <set> | |
| 10 #include <utility> | |
| 11 | |
| 12 #include "base/basictypes.h" | |
| 13 #include "base/containers/hash_tables.h" | |
| 14 #include "base/logging.h" | |
| 15 #include "base/memory/discardable_memory.h" | |
| 16 #include "base/memory/discardable_memory_android.h" | |
| 17 #include "base/memory/scoped_vector.h" | |
| 18 #include "base/synchronization/lock.h" | |
| 19 #include "base/threading/thread_checker.h" | |
| 20 | |
| 21 // The allocator consists of three parts (classes): | |
| 22 // - DiscardableMemoryAllocator: entry point of all allocations (through its | |
| 23 // Allocate() method) that are dispatched to the AshmemRegion instances (which | |
| 24 // it owns). | |
| 25 // - AshmemRegion: manages allocations and destructions inside a single large | |
| 26 // (e.g. 32 MBytes) ashmem region. | |
| 27 // - DiscardableAshmemChunk: class implementing the DiscardableMemory interface | |
| 28 // whose instances are returned to the client. DiscardableAshmemChunk lets the | |
| 29 // client seamlessly operate on a subrange of the ashmem region managed by | |
| 30 // AshmemRegion. | |
| 31 | |
| 32 namespace base { | |
| 33 namespace { | |
| 34 | |
| 35 // Only tolerate fragmentation in used chunks *caused by the client* (as opposed | |
| 36 // to the allocator when a free chunk is reused). The client can cause such | |
| 37 // fragmentation by e.g. requesting 4097 bytes. This size would be rounded up to | |
| 38 // 8192 by the allocator which would cause 4095 bytes of fragmentation (which is | |
| 39 // currently the maximum allowed). If the client requests 4096 bytes and a free | |
| 40 // chunk of 8192 bytes is available then the free chunk gets splitted into two | |
| 41 // pieces to minimize fragmentation (since 8192 - 4096 = 4096 which is greater | |
| 42 // than 4095). | |
| 43 // TODO(pliard): tune this if splitting chunks too often leads to performance | |
| 44 // issues. | |
| 45 const size_t kMaxChunkFragmentationBytes = 4096 - 1; | |
| 46 | |
| 47 } // namespace | |
| 48 | |
| 49 namespace internal { | |
| 50 | |
| 51 class DiscardableMemoryAllocator::DiscardableAshmemChunk | |
| 52 : public DiscardableMemory { | |
| 53 public: | |
| 54 // Note that |ashmem_region| must outlive |this|. | |
| 55 DiscardableAshmemChunk(AshmemRegion* ashmem_region, | |
| 56 int fd, | |
| 57 void* address, | |
| 58 size_t offset, | |
| 59 size_t size) | |
| 60 : ashmem_region_(ashmem_region), | |
| 61 fd_(fd), | |
| 62 address_(address), | |
| 63 offset_(offset), | |
| 64 size_(size), | |
| 65 locked_(true) { | |
| 66 } | |
| 67 | |
| 68 // Implemented below AshmemRegion since this requires the full definition of | |
| 69 // AshmemRegion. | |
| 70 virtual ~DiscardableAshmemChunk(); | |
| 71 | |
| 72 // DiscardableMemory: | |
| 73 virtual LockDiscardableMemoryStatus Lock() OVERRIDE { | |
| 74 DCHECK(!locked_); | |
| 75 locked_ = true; | |
| 76 return internal::LockAshmemRegion(fd_, offset_, size_, address_); | |
| 77 } | |
| 78 | |
| 79 virtual void Unlock() OVERRIDE { | |
| 80 DCHECK(locked_); | |
| 81 locked_ = false; | |
| 82 internal::UnlockAshmemRegion(fd_, offset_, size_, address_); | |
| 83 } | |
| 84 | |
| 85 virtual void* Memory() const OVERRIDE { | |
| 86 return address_; | |
| 87 } | |
| 88 | |
| 89 private: | |
| 90 AshmemRegion* const ashmem_region_; | |
| 91 const int fd_; | |
| 92 void* const address_; | |
| 93 const size_t offset_; | |
| 94 const size_t size_; | |
| 95 bool locked_; | |
| 96 | |
| 97 DISALLOW_COPY_AND_ASSIGN(DiscardableAshmemChunk); | |
| 98 }; | |
| 99 | |
| 100 class DiscardableMemoryAllocator::AshmemRegion { | |
| 101 public: | |
| 102 // Note that |allocator| must outlive |this|. | |
| 103 static scoped_ptr<AshmemRegion> Create( | |
| 104 size_t size, | |
| 105 const std::string& name, | |
| 106 DiscardableMemoryAllocator* allocator) { | |
| 107 int fd; | |
| 108 void* base; | |
| 109 if (!internal::CreateAshmemRegion(name.c_str(), size, &fd, &base)) | |
| 110 return scoped_ptr<AshmemRegion>(); | |
| 111 return make_scoped_ptr(new AshmemRegion(fd, size, base, allocator)); | |
| 112 } | |
| 113 | |
| 114 virtual ~AshmemRegion() { | |
| 115 const bool result = internal::CloseAshmemRegion(fd_, size_, base_); | |
| 116 DCHECK(result); | |
| 117 } | |
| 118 | |
| 119 // Returns a new instance of DiscardableMemory whose size is greater or equal | |
| 120 // than |actual_size| (which is expected to be greater or equal than | |
| 121 // |client_requested_size|). | |
| 122 // Allocation works as follows: | |
| 123 // 1) Reuse a previously freed chunk and return it if it succeeded. See | |
| 124 // ReuseFreeChunk_Locked() below for more information. | |
| 125 // 2) If no free chunk could be reused and the region is not big enough for | |
| 126 // the requested size then NULL is returned. | |
| 127 // 3) If there is enough room in the ashmem region then a new chunk is | |
| 128 // returned. This new chunk starts at |offset_| which is the end of the | |
| 129 // previously highest chunk in the region. | |
| 130 scoped_ptr<DiscardableMemory> Allocate_Locked(size_t client_requested_size, | |
| 131 size_t actual_size) { | |
| 132 DCHECK_LE(client_requested_size, actual_size); | |
| 133 allocator_->lock_.AssertAcquired(); | |
| 134 scoped_ptr<DiscardableMemory> memory = ReuseFreeChunk_Locked( | |
| 135 client_requested_size, actual_size); | |
| 136 if (memory) | |
| 137 return memory.Pass(); | |
| 138 if (size_ - offset_ < actual_size) { | |
| 139 // This region does not have enough space left to hold the requested size. | |
| 140 return scoped_ptr<DiscardableMemory>(); | |
| 141 } | |
| 142 void* const address = static_cast<char*>(base_) + offset_; | |
| 143 memory.reset( | |
| 144 new DiscardableAshmemChunk(this, fd_, address, offset_, actual_size)); | |
| 145 used_to_previous_chunk_map_.insert( | |
| 146 std::make_pair(address, highest_allocated_chunk_)); | |
| 147 highest_allocated_chunk_ = address; | |
| 148 offset_ += actual_size; | |
| 149 DCHECK_LE(offset_, size_); | |
| 150 return memory.Pass(); | |
| 151 } | |
| 152 | |
| 153 void OnChunkDeletion(void* chunk, size_t size) { | |
| 154 AutoLock auto_lock(allocator_->lock_); | |
| 155 MergeAndAddFreeChunk_Locked(chunk, size); | |
| 156 // Note that |this| might be deleted beyond this point. | |
| 157 } | |
| 158 | |
| 159 private: | |
| 160 struct FreeChunk { | |
| 161 FreeChunk(void* previous_chunk, void* start, size_t size) | |
| 162 : previous_chunk(previous_chunk), | |
| 163 start(start), | |
| 164 size(size) { | |
| 165 } | |
| 166 | |
| 167 void* const previous_chunk; | |
| 168 void* const start; | |
| 169 const size_t size; | |
| 170 | |
| 171 bool is_null() const { return !start; } | |
| 172 | |
| 173 bool operator<(const FreeChunk& other) const { | |
| 174 return size < other.size; | |
| 175 } | |
| 176 }; | |
| 177 | |
| 178 // Note that |allocator| must outlive |this|. | |
| 179 AshmemRegion(int fd, | |
| 180 size_t size, | |
| 181 void* base, | |
| 182 DiscardableMemoryAllocator* allocator) | |
| 183 : fd_(fd), | |
| 184 size_(size), | |
| 185 base_(base), | |
| 186 allocator_(allocator), | |
| 187 highest_allocated_chunk_(NULL), | |
| 188 offset_(0) { | |
| 189 DCHECK_GE(fd_, 0); | |
| 190 DCHECK_GE(size, kMinAshmemRegionSize); | |
| 191 DCHECK(base); | |
| 192 DCHECK(allocator); | |
| 193 } | |
| 194 | |
| 195 // Tries to reuse a previously freed chunk by doing a closest size match. | |
| 196 scoped_ptr<DiscardableMemory> ReuseFreeChunk_Locked( | |
| 197 size_t client_requested_size, | |
| 198 size_t actual_size) { | |
| 199 allocator_->lock_.AssertAcquired(); | |
| 200 const FreeChunk reused_chunk = RemoveFreeChunkFromIterator_Locked( | |
| 201 free_chunks_.lower_bound(FreeChunk(NULL, NULL, actual_size))); | |
| 202 if (reused_chunk.is_null()) | |
| 203 return scoped_ptr<DiscardableMemory>(); | |
| 204 | |
| 205 used_to_previous_chunk_map_.insert( | |
| 206 std::make_pair(reused_chunk.start, reused_chunk.previous_chunk)); | |
| 207 size_t reused_chunk_size = reused_chunk.size; | |
| 208 // |client_requested_size| is used below rather than |actual_size| to | |
| 209 // reflect the amount of bytes that would not be usable by the client (i.e. | |
| 210 // wasted). Using |actual_size| instead would not allow us to detect | |
| 211 // fragmentation caused by the client if he did misaligned allocations. | |
| 212 DCHECK_GE(reused_chunk.size, client_requested_size); | |
| 213 const size_t fragmentation_bytes = | |
| 214 reused_chunk.size - client_requested_size; | |
| 215 if (fragmentation_bytes > kMaxChunkFragmentationBytes) { | |
| 216 // Split the free chunk being recycled so that its unused tail doesn't get | |
| 217 // reused (i.e. locked) which would prevent it from being evicted under | |
| 218 // memory pressure. | |
| 219 reused_chunk_size = actual_size; | |
| 220 void* const new_chunk_start = | |
| 221 static_cast<char*>(reused_chunk.start) + actual_size; | |
| 222 DCHECK_GT(reused_chunk.size, actual_size); | |
| 223 const size_t new_chunk_size = reused_chunk.size - actual_size; | |
| 224 // Note that merging is not needed here since there can't be contiguous | |
| 225 // free chunks at this point. | |
| 226 AddFreeChunk_Locked( | |
| 227 FreeChunk(reused_chunk.start, new_chunk_start, new_chunk_size)); | |
| 228 } | |
| 229 const size_t offset = | |
| 230 static_cast<char*>(reused_chunk.start) - static_cast<char*>(base_); | |
| 231 internal::LockAshmemRegion( | |
| 232 fd_, offset, reused_chunk_size, reused_chunk.start); | |
| 233 scoped_ptr<DiscardableMemory> memory( | |
| 234 new DiscardableAshmemChunk(this, fd_, reused_chunk.start, offset, | |
| 235 reused_chunk_size)); | |
| 236 return memory.Pass(); | |
| 237 } | |
| 238 | |
| 239 // Makes the chunk identified with the provided arguments free and possibly | |
| 240 // merges this chunk with the previous and next contiguous ones. | |
| 241 // If the provided chunk is the only one used (and going to be freed) in the | |
| 242 // region then the internal ashmem region is closed so that the underlying | |
| 243 // physical pages are immediately released. | |
| 244 // Note that free chunks are unlocked therefore they can be reclaimed by the | |
| 245 // kernel if needed (under memory pressure) but they are not immediately | |
| 246 // released unfortunately since madvise(MADV_REMOVE) and | |
| 247 // fallocate(FALLOC_FL_PUNCH_HOLE) don't seem to work on ashmem. This might | |
| 248 // change in versions of kernel >=3.5 though. The fact that free chunks are | |
| 249 // not immediately released is the reason why we are trying to minimize | |
| 250 // fragmentation in order not to cause "artificial" memory pressure. | |
| 251 void MergeAndAddFreeChunk_Locked(void* chunk, size_t size) { | |
| 252 allocator_->lock_.AssertAcquired(); | |
| 253 size_t new_free_chunk_size = size; | |
| 254 // Merge with the previous chunk. | |
| 255 void* first_free_chunk = chunk; | |
| 256 DCHECK(!used_to_previous_chunk_map_.empty()); | |
| 257 const hash_map<void*, void*>::iterator previous_chunk_it = | |
| 258 used_to_previous_chunk_map_.find(chunk); | |
| 259 DCHECK(previous_chunk_it != used_to_previous_chunk_map_.end()); | |
| 260 void* previous_chunk = previous_chunk_it->second; | |
| 261 used_to_previous_chunk_map_.erase(previous_chunk_it); | |
| 262 if (previous_chunk) { | |
| 263 const FreeChunk free_chunk = RemoveFreeChunk_Locked(previous_chunk); | |
| 264 if (!free_chunk.is_null()) { | |
| 265 new_free_chunk_size += free_chunk.size; | |
| 266 first_free_chunk = previous_chunk; | |
| 267 // There should not be more contiguous previous free chunks. | |
| 268 DCHECK(!address_to_free_chunk_map_.count(free_chunk.previous_chunk)); | |
| 269 } | |
| 270 } | |
| 271 // Merge with the next chunk if free and present. | |
| 272 void* next_chunk = static_cast<char*>(chunk) + size; | |
| 273 const FreeChunk next_free_chunk = RemoveFreeChunk_Locked(next_chunk); | |
| 274 if (!next_free_chunk.is_null()) { | |
| 275 new_free_chunk_size += next_free_chunk.size; | |
| 276 // Same as above. | |
| 277 DCHECK(!address_to_free_chunk_map_.count(static_cast<char*>(next_chunk) + | |
| 278 next_free_chunk.size)); | |
| 279 } | |
| 280 const bool whole_ashmem_region_is_free = | |
| 281 used_to_previous_chunk_map_.empty(); | |
| 282 if (!whole_ashmem_region_is_free) { | |
| 283 AddFreeChunk_Locked( | |
| 284 FreeChunk(previous_chunk, first_free_chunk, new_free_chunk_size)); | |
| 285 return; | |
| 286 } | |
| 287 // The whole ashmem region is free thus it can be deleted. | |
| 288 DCHECK_EQ(base_, first_free_chunk); | |
| 289 DCHECK(free_chunks_.empty()); | |
| 290 DCHECK(address_to_free_chunk_map_.empty()); | |
| 291 DCHECK(used_to_previous_chunk_map_.empty()); | |
| 292 allocator_->DeleteAshmemRegion_Locked(this); // Deletes |this|. | |
| 293 } | |
| 294 | |
| 295 void AddFreeChunk_Locked(const FreeChunk& free_chunk) { | |
| 296 allocator_->lock_.AssertAcquired(); | |
| 297 const std::multiset<FreeChunk>::iterator it = free_chunks_.insert( | |
| 298 free_chunk); | |
| 299 address_to_free_chunk_map_.insert(std::make_pair(free_chunk.start, it)); | |
| 300 // Update the next used contiguous chunk, if any, since its previous chunk | |
| 301 // may have changed due to free chunks merging/splitting. | |
| 302 void* const next_used_contiguous_chunk = | |
| 303 static_cast<char*>(free_chunk.start) + free_chunk.size; | |
| 304 hash_map<void*, void*>::iterator previous_it = | |
| 305 used_to_previous_chunk_map_.find(next_used_contiguous_chunk); | |
| 306 if (previous_it != used_to_previous_chunk_map_.end()) | |
| 307 previous_it->second = free_chunk.start; | |
| 308 } | |
| 309 | |
| 310 // Finds and removes the free chunk, if any, whose start address is | |
| 311 // |chunk_start|. Returns a copy of the unlinked free chunk or a free chunk | |
| 312 // whose content is null if it was not found. | |
| 313 FreeChunk RemoveFreeChunk_Locked(void* chunk_start) { | |
| 314 allocator_->lock_.AssertAcquired(); | |
| 315 const hash_map< | |
| 316 void*, std::multiset<FreeChunk>::iterator>::iterator it = | |
| 317 address_to_free_chunk_map_.find(chunk_start); | |
| 318 if (it == address_to_free_chunk_map_.end()) | |
| 319 return FreeChunk(NULL, NULL, 0U); | |
| 320 return RemoveFreeChunkFromIterator_Locked(it->second); | |
| 321 } | |
| 322 | |
| 323 // Same as above but takes an iterator in. | |
| 324 FreeChunk RemoveFreeChunkFromIterator_Locked( | |
| 325 std::multiset<FreeChunk>::iterator free_chunk_it) { | |
| 326 allocator_->lock_.AssertAcquired(); | |
| 327 if (free_chunk_it == free_chunks_.end()) | |
| 328 return FreeChunk(NULL, NULL, 0U); | |
| 329 DCHECK(free_chunk_it != free_chunks_.end()); | |
| 330 const FreeChunk free_chunk(*free_chunk_it); | |
| 331 address_to_free_chunk_map_.erase(free_chunk_it->start); | |
| 332 free_chunks_.erase(free_chunk_it); | |
| 333 return free_chunk; | |
| 334 } | |
| 335 | |
| 336 const int fd_; | |
| 337 const size_t size_; | |
| 338 void* const base_; | |
| 339 DiscardableMemoryAllocator* const allocator_; | |
| 340 void* highest_allocated_chunk_; | |
| 341 // Points to the end of |highest_allocated_chunk_|. | |
| 342 size_t offset_; | |
| 343 // Allows free chunks recycling (lookup, insertion and removal) in O(log N). | |
| 344 // Note that FreeChunk values are indexed by their size and also note that | |
| 345 // multiple free chunks can have the same size (which is why multiset<> is | |
| 346 // used instead of e.g. set<>). | |
| 347 std::multiset<FreeChunk> free_chunks_; | |
| 348 // Used while merging free contiguous chunks to erase free chunks (from their | |
| 349 // start address) in constant time. Note that multiset<>::{insert,erase}() | |
| 350 // don't invalidate iterators (except the one for the element being removed | |
| 351 // obviously). | |
| 352 hash_map< | |
| 353 void*, std::multiset<FreeChunk>::iterator> address_to_free_chunk_map_; | |
| 354 // Maps the address of *used* chunks to the address of their previous | |
| 355 // contiguous chunk. | |
| 356 hash_map<void*, void*> used_to_previous_chunk_map_; | |
| 357 | |
| 358 DISALLOW_COPY_AND_ASSIGN(AshmemRegion); | |
| 359 }; | |
| 360 | |
| 361 DiscardableMemoryAllocator::DiscardableAshmemChunk::~DiscardableAshmemChunk() { | |
| 362 if (locked_) | |
| 363 internal::UnlockAshmemRegion(fd_, offset_, size_, address_); | |
| 364 ashmem_region_->OnChunkDeletion(address_, size_); | |
| 365 } | |
| 366 | |
| 367 DiscardableMemoryAllocator::DiscardableMemoryAllocator(const std::string& name) | |
| 368 : name_(name) { | |
| 369 } | |
| 370 | |
| 371 DiscardableMemoryAllocator::~DiscardableMemoryAllocator() { | |
| 372 DCHECK(thread_checker_.CalledOnValidThread()); | |
| 373 DCHECK(ashmem_regions_.empty()); | |
| 374 } | |
| 375 | |
| 376 scoped_ptr<DiscardableMemory> DiscardableMemoryAllocator::Allocate( | |
| 377 size_t size) { | |
| 378 const size_t aligned_size = internal::AlignToNextPage(size); | |
| 379 // TODO(pliard): make this function less naive by e.g. moving the free chunks | |
| 380 // multiset to the allocator itself in order to decrease even more | |
| 381 // fragmentation/speedup allocation. Note that there should not be more than a | |
| 382 // couple (=5) of AshmemRegion instances in practice though. | |
| 383 AutoLock auto_lock(lock_); | |
| 384 DCHECK_LE(ashmem_regions_.size(), 5U); | |
| 385 for (ScopedVector<AshmemRegion>::iterator it = ashmem_regions_.begin(); | |
| 386 it != ashmem_regions_.end(); ++it) { | |
| 387 scoped_ptr<DiscardableMemory> memory( | |
| 388 (*it)->Allocate_Locked(size, aligned_size)); | |
| 389 if (memory) | |
| 390 return memory.Pass(); | |
| 391 } | |
| 392 scoped_ptr<AshmemRegion> new_region( | |
| 393 AshmemRegion::Create( | |
| 394 std::max(static_cast<size_t>(kMinAshmemRegionSize), aligned_size), | |
| 395 name_.c_str(), this)); | |
| 396 if (!new_region) { | |
| 397 // TODO(pliard): consider adding an histogram to see how often this happens. | |
| 398 return scoped_ptr<DiscardableMemory>(); | |
| 399 } | |
| 400 ashmem_regions_.push_back(new_region.release()); | |
| 401 return ashmem_regions_.back()->Allocate_Locked(size, aligned_size); | |
| 402 } | |
| 403 | |
| 404 void DiscardableMemoryAllocator::DeleteAshmemRegion_Locked( | |
| 405 AshmemRegion* region) { | |
| 406 lock_.AssertAcquired(); | |
| 407 // Note that there should not be more than a couple of ashmem region instances | |
| 408 // in |ashmem_regions_|. | |
| 409 DCHECK_LE(ashmem_regions_.size(), 5U); | |
| 410 const ScopedVector<AshmemRegion>::iterator it = std::find( | |
| 411 ashmem_regions_.begin(), ashmem_regions_.end(), region); | |
| 412 DCHECK_NE(ashmem_regions_.end(), it); | |
| 413 std::swap(*it, ashmem_regions_.back()); | |
| 414 ashmem_regions_.pop_back(); | |
| 415 } | |
| 416 | |
| 417 } // namespace internal | |
| 418 } // namespace base | |
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Chromium Code Reviews
Issue 100103003:
Revert 239763 "Add DiscardableMemoryAllocator to minimize use of..." (Closed)
Base URL: svn://svn.chromium.org/chrome/