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| 1 // Copyright 2014 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_ashmem_allocator.h" | |
| 6 | |
| 7 #include <sys/mman.h> | |
| 8 #include <unistd.h> | |
| 9 | |
| 10 #include <algorithm> | |
| 11 #include <cmath> | |
| 12 #include <limits> | |
| 13 #include <set> | |
| 14 #include <utility> | |
| 15 | |
| 16 #include "base/basictypes.h" | |
| 17 #include "base/containers/hash_tables.h" | |
| 18 #include "base/files/file_util.h" | |
| 19 #include "base/files/scoped_file.h" | |
| 20 #include "base/logging.h" | |
| 21 #include "base/memory/scoped_vector.h" | |
| 22 #include "third_party/ashmem/ashmem.h" | |
| 23 | |
| 24 // The allocator consists of three parts (classes): | |
| 25 // - DiscardableMemoryAshmemAllocator: entry point of all allocations (through | |
| 26 // its Allocate() method) that are dispatched to the AshmemRegion instances | |
| 27 // (which it owns). | |
| 28 // - AshmemRegion: manages allocations and destructions inside a single large | |
| 29 // (e.g. 32 MBytes) ashmem region. | |
| 30 // - DiscardableAshmemChunk: class mimicking the DiscardableMemory interface | |
| 31 // whose instances are returned to the client. | |
| 32 | |
| 33 namespace base { | |
| 34 namespace { | |
| 35 | |
| 36 // Only tolerate fragmentation in used chunks *caused by the client* (as opposed | |
| 37 // to the allocator when a free chunk is reused). The client can cause such | |
| 38 // fragmentation by e.g. requesting 4097 bytes. This size would be rounded up to | |
| 39 // 8192 by the allocator which would cause 4095 bytes of fragmentation (which is | |
| 40 // currently the maximum allowed). If the client requests 4096 bytes and a free | |
| 41 // chunk of 8192 bytes is available then the free chunk gets splitted into two | |
| 42 // pieces to minimize fragmentation (since 8192 - 4096 = 4096 which is greater | |
| 43 // than 4095). | |
| 44 // TODO(pliard): tune this if splitting chunks too often leads to performance | |
| 45 // issues. | |
| 46 const size_t kMaxChunkFragmentationBytes = 4096 - 1; | |
| 47 | |
| 48 const size_t kMinAshmemRegionSize = 32 * 1024 * 1024; | |
| 49 | |
| 50 // Returns 0 if the provided size is too high to be aligned. | |
| 51 size_t AlignToNextPage(size_t size) { | |
| 52 const size_t kPageSize = 4096; | |
| 53 DCHECK_EQ(static_cast<int>(kPageSize), getpagesize()); | |
| 54 if (size > std::numeric_limits<size_t>::max() - kPageSize + 1) | |
| 55 return 0; | |
| 56 const size_t mask = ~(kPageSize - 1); | |
| 57 return (size + kPageSize - 1) & mask; | |
| 58 } | |
| 59 | |
| 60 bool CreateAshmemRegion(const char* name, | |
| 61 size_t size, | |
| 62 int* out_fd, | |
| 63 uintptr_t* out_address) { | |
| 64 base::ScopedFD fd(ashmem_create_region(name, size)); | |
| 65 if (!fd.is_valid()) { | |
| 66 DLOG(ERROR) << "ashmem_create_region() failed"; | |
| 67 return false; | |
| 68 } | |
| 69 | |
| 70 const int err = ashmem_set_prot_region(fd.get(), PROT_READ | PROT_WRITE); | |
| 71 if (err < 0) { | |
| 72 DLOG(ERROR) << "Error " << err << " when setting protection of ashmem"; | |
| 73 return false; | |
| 74 } | |
| 75 | |
| 76 // There is a problem using MAP_PRIVATE here. As we are constantly calling | |
| 77 // Lock() and Unlock(), data could get lost if they are not written to the | |
| 78 // underlying file when Unlock() gets called. | |
| 79 void* const address = mmap( | |
| 80 NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd.get(), 0); | |
| 81 if (address == MAP_FAILED) { | |
| 82 DPLOG(ERROR) << "Failed to map memory."; | |
| 83 return false; | |
| 84 } | |
| 85 | |
| 86 *out_fd = fd.release(); | |
| 87 *out_address = reinterpret_cast<uintptr_t>(address); | |
| 88 return true; | |
| 89 } | |
| 90 | |
| 91 bool CloseAshmemRegion(int fd, size_t size, void* address) { | |
| 92 if (munmap(address, size) == -1) { | |
| 93 DPLOG(ERROR) << "Failed to unmap memory."; | |
| 94 close(fd); | |
| 95 return false; | |
| 96 } | |
| 97 return close(fd) == 0; | |
| 98 } | |
| 99 | |
| 100 bool LockAshmemRegion(int fd, size_t off, size_t size) { | |
| 101 return ashmem_pin_region(fd, off, size) != ASHMEM_WAS_PURGED; | |
| 102 } | |
| 103 | |
| 104 bool UnlockAshmemRegion(int fd, size_t off, size_t size) { | |
| 105 const int failed = ashmem_unpin_region(fd, off, size); | |
| 106 if (failed) | |
| 107 DLOG(ERROR) << "Failed to unpin memory."; | |
| 108 return !failed; | |
| 109 } | |
| 110 | |
| 111 } // namespace | |
| 112 | |
| 113 namespace internal { | |
| 114 | |
| 115 class AshmemRegion { | |
| 116 public: | |
| 117 // Note that |allocator| must outlive |this|. | |
| 118 static scoped_ptr<AshmemRegion> Create( | |
| 119 size_t size, | |
| 120 const std::string& name, | |
| 121 DiscardableMemoryAshmemAllocator* allocator) { | |
| 122 DCHECK_EQ(size, AlignToNextPage(size)); | |
| 123 int fd; | |
| 124 uintptr_t base; | |
| 125 if (!CreateAshmemRegion(name.c_str(), size, &fd, &base)) | |
| 126 return scoped_ptr<AshmemRegion>(); | |
| 127 return make_scoped_ptr(new AshmemRegion(fd, size, base, allocator)); | |
| 128 } | |
| 129 | |
| 130 ~AshmemRegion() { | |
| 131 const bool result = CloseAshmemRegion( | |
| 132 fd_, size_, reinterpret_cast<void*>(base_)); | |
| 133 DCHECK(result); | |
| 134 DCHECK(!highest_allocated_chunk_); | |
| 135 } | |
| 136 | |
| 137 // Returns a new instance of DiscardableAshmemChunk whose size is greater or | |
| 138 // equal than |actual_size| (which is expected to be greater or equal than | |
| 139 // |client_requested_size|). | |
| 140 // Allocation works as follows: | |
| 141 // 1) Reuse a previously freed chunk and return it if it succeeded. See | |
| 142 // ReuseFreeChunk_Locked() below for more information. | |
| 143 // 2) If no free chunk could be reused and the region is not big enough for | |
| 144 // the requested size then NULL is returned. | |
| 145 // 3) If there is enough room in the ashmem region then a new chunk is | |
| 146 // returned. This new chunk starts at |offset_| which is the end of the | |
| 147 // previously highest chunk in the region. | |
| 148 scoped_ptr<DiscardableAshmemChunk> Allocate_Locked( | |
| 149 size_t client_requested_size, | |
| 150 size_t actual_size) { | |
| 151 DCHECK_LE(client_requested_size, actual_size); | |
| 152 allocator_->lock_.AssertAcquired(); | |
| 153 | |
| 154 // Check that the |highest_allocated_chunk_| field doesn't contain a stale | |
| 155 // pointer. It should point to either a free chunk or a used chunk. | |
| 156 DCHECK(!highest_allocated_chunk_ || | |
| 157 address_to_free_chunk_map_.find(highest_allocated_chunk_) != | |
| 158 address_to_free_chunk_map_.end() || | |
| 159 used_to_previous_chunk_map_.find(highest_allocated_chunk_) != | |
| 160 used_to_previous_chunk_map_.end()); | |
| 161 | |
| 162 scoped_ptr<DiscardableAshmemChunk> memory = ReuseFreeChunk_Locked( | |
| 163 client_requested_size, actual_size); | |
| 164 if (memory) | |
| 165 return memory.Pass(); | |
| 166 | |
| 167 if (size_ - offset_ < actual_size) { | |
| 168 // This region does not have enough space left to hold the requested size. | |
| 169 return scoped_ptr<DiscardableAshmemChunk>(); | |
| 170 } | |
| 171 | |
| 172 uintptr_t const address = base_ + offset_; | |
| 173 memory.reset( | |
| 174 new DiscardableAshmemChunk(this, fd_, reinterpret_cast<void*>(address), | |
| 175 offset_, actual_size)); | |
| 176 | |
| 177 used_to_previous_chunk_map_.insert( | |
| 178 std::make_pair(address, highest_allocated_chunk_)); | |
| 179 highest_allocated_chunk_ = reinterpret_cast<uintptr_t>(address); | |
| 180 offset_ += actual_size; | |
| 181 DCHECK_LE(offset_, size_); | |
| 182 return memory.Pass(); | |
| 183 } | |
| 184 | |
| 185 void OnChunkDeletion(uintptr_t chunk, size_t size) { | |
| 186 AutoLock auto_lock(allocator_->lock_); | |
| 187 MergeAndAddFreeChunk_Locked(chunk, size); | |
| 188 // Note that |this| might be deleted beyond this point. | |
| 189 } | |
| 190 | |
| 191 private: | |
| 192 struct FreeChunk { | |
| 193 FreeChunk() : previous_chunk(0), start(0), size(0) {} | |
| 194 | |
| 195 explicit FreeChunk(size_t size) | |
| 196 : previous_chunk(0), | |
| 197 start(0), | |
| 198 size(size) { | |
| 199 } | |
| 200 | |
| 201 FreeChunk(uintptr_t previous_chunk, uintptr_t start, size_t size) | |
| 202 : previous_chunk(previous_chunk), | |
| 203 start(start), | |
| 204 size(size) { | |
| 205 DCHECK_LT(previous_chunk, start); | |
| 206 } | |
| 207 | |
| 208 uintptr_t const previous_chunk; | |
| 209 uintptr_t const start; | |
| 210 const size_t size; | |
| 211 | |
| 212 bool is_null() const { return !start; } | |
| 213 | |
| 214 bool operator<(const FreeChunk& other) const { | |
| 215 return size < other.size; | |
| 216 } | |
| 217 }; | |
| 218 | |
| 219 // Note that |allocator| must outlive |this|. | |
| 220 AshmemRegion(int fd, | |
| 221 size_t size, | |
| 222 uintptr_t base, | |
| 223 DiscardableMemoryAshmemAllocator* allocator) | |
| 224 : fd_(fd), | |
| 225 size_(size), | |
| 226 base_(base), | |
| 227 allocator_(allocator), | |
| 228 highest_allocated_chunk_(0), | |
| 229 offset_(0) { | |
| 230 DCHECK_GE(fd_, 0); | |
| 231 DCHECK_GE(size, kMinAshmemRegionSize); | |
| 232 DCHECK(base); | |
| 233 DCHECK(allocator); | |
| 234 } | |
| 235 | |
| 236 // Tries to reuse a previously freed chunk by doing a closest size match. | |
| 237 scoped_ptr<DiscardableAshmemChunk> ReuseFreeChunk_Locked( | |
| 238 size_t client_requested_size, | |
| 239 size_t actual_size) { | |
| 240 allocator_->lock_.AssertAcquired(); | |
| 241 const FreeChunk reused_chunk = RemoveFreeChunkFromIterator_Locked( | |
| 242 free_chunks_.lower_bound(FreeChunk(actual_size))); | |
| 243 if (reused_chunk.is_null()) | |
| 244 return scoped_ptr<DiscardableAshmemChunk>(); | |
| 245 | |
| 246 used_to_previous_chunk_map_.insert( | |
| 247 std::make_pair(reused_chunk.start, reused_chunk.previous_chunk)); | |
| 248 size_t reused_chunk_size = reused_chunk.size; | |
| 249 // |client_requested_size| is used below rather than |actual_size| to | |
| 250 // reflect the amount of bytes that would not be usable by the client (i.e. | |
| 251 // wasted). Using |actual_size| instead would not allow us to detect | |
| 252 // fragmentation caused by the client if he did misaligned allocations. | |
| 253 DCHECK_GE(reused_chunk.size, client_requested_size); | |
| 254 const size_t fragmentation_bytes = | |
| 255 reused_chunk.size - client_requested_size; | |
| 256 | |
| 257 if (fragmentation_bytes > kMaxChunkFragmentationBytes) { | |
| 258 // Split the free chunk being recycled so that its unused tail doesn't get | |
| 259 // reused (i.e. locked) which would prevent it from being evicted under | |
| 260 // memory pressure. | |
| 261 reused_chunk_size = actual_size; | |
| 262 uintptr_t const new_chunk_start = reused_chunk.start + actual_size; | |
| 263 if (reused_chunk.start == highest_allocated_chunk_) { | |
| 264 // We also need to update the pointer to the highest allocated chunk in | |
| 265 // case we are splitting the highest chunk. | |
| 266 highest_allocated_chunk_ = new_chunk_start; | |
| 267 } | |
| 268 DCHECK_GT(reused_chunk.size, actual_size); | |
| 269 const size_t new_chunk_size = reused_chunk.size - actual_size; | |
| 270 // Note that merging is not needed here since there can't be contiguous | |
| 271 // free chunks at this point. | |
| 272 AddFreeChunk_Locked( | |
| 273 FreeChunk(reused_chunk.start, new_chunk_start, new_chunk_size)); | |
| 274 } | |
| 275 | |
| 276 const size_t offset = reused_chunk.start - base_; | |
| 277 LockAshmemRegion(fd_, offset, reused_chunk_size); | |
| 278 scoped_ptr<DiscardableAshmemChunk> memory( | |
| 279 new DiscardableAshmemChunk(this, fd_, | |
| 280 reinterpret_cast<void*>(reused_chunk.start), | |
| 281 offset, reused_chunk_size)); | |
| 282 return memory.Pass(); | |
| 283 } | |
| 284 | |
| 285 // Makes the chunk identified with the provided arguments free and possibly | |
| 286 // merges this chunk with the previous and next contiguous ones. | |
| 287 // If the provided chunk is the only one used (and going to be freed) in the | |
| 288 // region then the internal ashmem region is closed so that the underlying | |
| 289 // physical pages are immediately released. | |
| 290 // Note that free chunks are unlocked therefore they can be reclaimed by the | |
| 291 // kernel if needed (under memory pressure) but they are not immediately | |
| 292 // released unfortunately since madvise(MADV_REMOVE) and | |
| 293 // fallocate(FALLOC_FL_PUNCH_HOLE) don't seem to work on ashmem. This might | |
| 294 // change in versions of kernel >=3.5 though. The fact that free chunks are | |
| 295 // not immediately released is the reason why we are trying to minimize | |
| 296 // fragmentation in order not to cause "artificial" memory pressure. | |
| 297 void MergeAndAddFreeChunk_Locked(uintptr_t chunk, size_t size) { | |
| 298 allocator_->lock_.AssertAcquired(); | |
| 299 size_t new_free_chunk_size = size; | |
| 300 // Merge with the previous chunk. | |
| 301 uintptr_t first_free_chunk = chunk; | |
| 302 DCHECK(!used_to_previous_chunk_map_.empty()); | |
| 303 const hash_map<uintptr_t, uintptr_t>::iterator previous_chunk_it = | |
| 304 used_to_previous_chunk_map_.find(chunk); | |
| 305 DCHECK(previous_chunk_it != used_to_previous_chunk_map_.end()); | |
| 306 uintptr_t previous_chunk = previous_chunk_it->second; | |
| 307 used_to_previous_chunk_map_.erase(previous_chunk_it); | |
| 308 | |
| 309 if (previous_chunk) { | |
| 310 const FreeChunk free_chunk = RemoveFreeChunk_Locked(previous_chunk); | |
| 311 if (!free_chunk.is_null()) { | |
| 312 new_free_chunk_size += free_chunk.size; | |
| 313 first_free_chunk = previous_chunk; | |
| 314 if (chunk == highest_allocated_chunk_) | |
| 315 highest_allocated_chunk_ = previous_chunk; | |
| 316 | |
| 317 // There should not be more contiguous previous free chunks. | |
| 318 previous_chunk = free_chunk.previous_chunk; | |
| 319 DCHECK(!address_to_free_chunk_map_.count(previous_chunk)); | |
| 320 } | |
| 321 } | |
| 322 | |
| 323 // Merge with the next chunk if free and present. | |
| 324 uintptr_t next_chunk = chunk + size; | |
| 325 const FreeChunk next_free_chunk = RemoveFreeChunk_Locked(next_chunk); | |
| 326 if (!next_free_chunk.is_null()) { | |
| 327 new_free_chunk_size += next_free_chunk.size; | |
| 328 if (next_free_chunk.start == highest_allocated_chunk_) | |
| 329 highest_allocated_chunk_ = first_free_chunk; | |
| 330 | |
| 331 // Same as above. | |
| 332 DCHECK( | |
| 333 !address_to_free_chunk_map_.count(next_chunk + next_free_chunk.size)); | |
| 334 } | |
| 335 | |
| 336 const bool whole_ashmem_region_is_free = | |
| 337 used_to_previous_chunk_map_.empty(); | |
| 338 if (!whole_ashmem_region_is_free) { | |
| 339 AddFreeChunk_Locked( | |
| 340 FreeChunk(previous_chunk, first_free_chunk, new_free_chunk_size)); | |
| 341 return; | |
| 342 } | |
| 343 | |
| 344 // The whole ashmem region is free thus it can be deleted. | |
| 345 DCHECK_EQ(base_, first_free_chunk); | |
| 346 DCHECK_EQ(base_, highest_allocated_chunk_); | |
| 347 DCHECK(free_chunks_.empty()); | |
| 348 DCHECK(address_to_free_chunk_map_.empty()); | |
| 349 DCHECK(used_to_previous_chunk_map_.empty()); | |
| 350 highest_allocated_chunk_ = 0; | |
| 351 allocator_->DeleteAshmemRegion_Locked(this); // Deletes |this|. | |
| 352 } | |
| 353 | |
| 354 void AddFreeChunk_Locked(const FreeChunk& free_chunk) { | |
| 355 allocator_->lock_.AssertAcquired(); | |
| 356 const std::multiset<FreeChunk>::iterator it = free_chunks_.insert( | |
| 357 free_chunk); | |
| 358 address_to_free_chunk_map_.insert(std::make_pair(free_chunk.start, it)); | |
| 359 // Update the next used contiguous chunk, if any, since its previous chunk | |
| 360 // may have changed due to free chunks merging/splitting. | |
| 361 uintptr_t const next_used_contiguous_chunk = | |
| 362 free_chunk.start + free_chunk.size; | |
| 363 hash_map<uintptr_t, uintptr_t>::iterator previous_it = | |
| 364 used_to_previous_chunk_map_.find(next_used_contiguous_chunk); | |
| 365 if (previous_it != used_to_previous_chunk_map_.end()) | |
| 366 previous_it->second = free_chunk.start; | |
| 367 } | |
| 368 | |
| 369 // Finds and removes the free chunk, if any, whose start address is | |
| 370 // |chunk_start|. Returns a copy of the unlinked free chunk or a free chunk | |
| 371 // whose content is null if it was not found. | |
| 372 FreeChunk RemoveFreeChunk_Locked(uintptr_t chunk_start) { | |
| 373 allocator_->lock_.AssertAcquired(); | |
| 374 const hash_map< | |
| 375 uintptr_t, std::multiset<FreeChunk>::iterator>::iterator it = | |
| 376 address_to_free_chunk_map_.find(chunk_start); | |
| 377 if (it == address_to_free_chunk_map_.end()) | |
| 378 return FreeChunk(); | |
| 379 return RemoveFreeChunkFromIterator_Locked(it->second); | |
| 380 } | |
| 381 | |
| 382 // Same as above but takes an iterator in. | |
| 383 FreeChunk RemoveFreeChunkFromIterator_Locked( | |
| 384 std::multiset<FreeChunk>::iterator free_chunk_it) { | |
| 385 allocator_->lock_.AssertAcquired(); | |
| 386 if (free_chunk_it == free_chunks_.end()) | |
| 387 return FreeChunk(); | |
| 388 DCHECK(free_chunk_it != free_chunks_.end()); | |
| 389 const FreeChunk free_chunk(*free_chunk_it); | |
| 390 address_to_free_chunk_map_.erase(free_chunk_it->start); | |
| 391 free_chunks_.erase(free_chunk_it); | |
| 392 return free_chunk; | |
| 393 } | |
| 394 | |
| 395 const int fd_; | |
| 396 const size_t size_; | |
| 397 uintptr_t const base_; | |
| 398 DiscardableMemoryAshmemAllocator* const allocator_; | |
| 399 // Points to the chunk with the highest address in the region. This pointer | |
| 400 // needs to be carefully updated when chunks are merged/split. | |
| 401 uintptr_t highest_allocated_chunk_; | |
| 402 // Points to the end of |highest_allocated_chunk_|. | |
| 403 size_t offset_; | |
| 404 // Allows free chunks recycling (lookup, insertion and removal) in O(log N). | |
| 405 // Note that FreeChunk values are indexed by their size and also note that | |
| 406 // multiple free chunks can have the same size (which is why multiset<> is | |
| 407 // used instead of e.g. set<>). | |
| 408 std::multiset<FreeChunk> free_chunks_; | |
| 409 // Used while merging free contiguous chunks to erase free chunks (from their | |
| 410 // start address) in constant time. Note that multiset<>::{insert,erase}() | |
| 411 // don't invalidate iterators (except the one for the element being removed | |
| 412 // obviously). | |
| 413 hash_map< | |
| 414 uintptr_t, std::multiset<FreeChunk>::iterator> address_to_free_chunk_map_; | |
| 415 // Maps the address of *used* chunks to the address of their previous | |
| 416 // contiguous chunk. | |
| 417 hash_map<uintptr_t, uintptr_t> used_to_previous_chunk_map_; | |
| 418 | |
| 419 DISALLOW_COPY_AND_ASSIGN(AshmemRegion); | |
| 420 }; | |
| 421 | |
| 422 DiscardableAshmemChunk::~DiscardableAshmemChunk() { | |
| 423 if (locked_) | |
| 424 UnlockAshmemRegion(fd_, offset_, size_); | |
| 425 ashmem_region_->OnChunkDeletion(reinterpret_cast<uintptr_t>(address_), size_); | |
| 426 } | |
| 427 | |
| 428 bool DiscardableAshmemChunk::Lock() { | |
| 429 DCHECK(!locked_); | |
| 430 locked_ = true; | |
| 431 return LockAshmemRegion(fd_, offset_, size_); | |
| 432 } | |
| 433 | |
| 434 void DiscardableAshmemChunk::Unlock() { | |
| 435 DCHECK(locked_); | |
| 436 locked_ = false; | |
| 437 UnlockAshmemRegion(fd_, offset_, size_); | |
| 438 } | |
| 439 | |
| 440 void* DiscardableAshmemChunk::Memory() const { | |
| 441 return address_; | |
| 442 } | |
| 443 | |
| 444 // Note that |ashmem_region| must outlive |this|. | |
| 445 DiscardableAshmemChunk::DiscardableAshmemChunk(AshmemRegion* ashmem_region, | |
| 446 int fd, | |
| 447 void* address, | |
| 448 size_t offset, | |
| 449 size_t size) | |
| 450 : ashmem_region_(ashmem_region), | |
| 451 fd_(fd), | |
| 452 address_(address), | |
| 453 offset_(offset), | |
| 454 size_(size), | |
| 455 locked_(true) { | |
| 456 } | |
| 457 | |
| 458 DiscardableMemoryAshmemAllocator::DiscardableMemoryAshmemAllocator( | |
| 459 const std::string& name, | |
| 460 size_t ashmem_region_size) | |
| 461 : name_(name), | |
| 462 ashmem_region_size_( | |
| 463 std::max(kMinAshmemRegionSize, AlignToNextPage(ashmem_region_size))), | |
| 464 last_ashmem_region_size_(0) { | |
| 465 DCHECK_GE(ashmem_region_size_, kMinAshmemRegionSize); | |
| 466 } | |
| 467 | |
| 468 DiscardableMemoryAshmemAllocator::~DiscardableMemoryAshmemAllocator() { | |
| 469 DCHECK(ashmem_regions_.empty()); | |
| 470 } | |
| 471 | |
| 472 scoped_ptr<DiscardableAshmemChunk> DiscardableMemoryAshmemAllocator::Allocate( | |
| 473 size_t size) { | |
| 474 const size_t aligned_size = AlignToNextPage(size); | |
| 475 if (!aligned_size) | |
| 476 return scoped_ptr<DiscardableAshmemChunk>(); | |
| 477 // TODO(pliard): make this function less naive by e.g. moving the free chunks | |
| 478 // multiset to the allocator itself in order to decrease even more | |
| 479 // fragmentation/speedup allocation. Note that there should not be more than a | |
| 480 // couple (=5) of AshmemRegion instances in practice though. | |
| 481 AutoLock auto_lock(lock_); | |
| 482 DCHECK_LE(ashmem_regions_.size(), 5U); | |
| 483 for (ScopedVector<AshmemRegion>::iterator it = ashmem_regions_.begin(); | |
| 484 it != ashmem_regions_.end(); ++it) { | |
| 485 scoped_ptr<DiscardableAshmemChunk> memory( | |
| 486 (*it)->Allocate_Locked(size, aligned_size)); | |
| 487 if (memory) | |
| 488 return memory.Pass(); | |
| 489 } | |
| 490 // The creation of the (large) ashmem region might fail if the address space | |
| 491 // is too fragmented. In case creation fails the allocator retries by | |
| 492 // repetitively dividing the size by 2. | |
| 493 const size_t min_region_size = std::max(kMinAshmemRegionSize, aligned_size); | |
| 494 for (size_t region_size = std::max(ashmem_region_size_, aligned_size); | |
| 495 region_size >= min_region_size; | |
| 496 region_size = AlignToNextPage(region_size / 2)) { | |
| 497 scoped_ptr<AshmemRegion> new_region( | |
| 498 AshmemRegion::Create(region_size, name_.c_str(), this)); | |
| 499 if (!new_region) | |
| 500 continue; | |
| 501 last_ashmem_region_size_ = region_size; | |
| 502 ashmem_regions_.push_back(new_region.release()); | |
| 503 return ashmem_regions_.back()->Allocate_Locked(size, aligned_size); | |
| 504 } | |
| 505 // TODO(pliard): consider adding an histogram to see how often this happens. | |
| 506 return scoped_ptr<DiscardableAshmemChunk>(); | |
| 507 } | |
| 508 | |
| 509 size_t DiscardableMemoryAshmemAllocator::last_ashmem_region_size() const { | |
| 510 AutoLock auto_lock(lock_); | |
| 511 return last_ashmem_region_size_; | |
| 512 } | |
| 513 | |
| 514 void DiscardableMemoryAshmemAllocator::DeleteAshmemRegion_Locked( | |
| 515 AshmemRegion* region) { | |
| 516 lock_.AssertAcquired(); | |
| 517 // Note that there should not be more than a couple of ashmem region instances | |
| 518 // in |ashmem_regions_|. | |
| 519 DCHECK_LE(ashmem_regions_.size(), 5U); | |
| 520 const ScopedVector<AshmemRegion>::iterator it = std::find( | |
| 521 ashmem_regions_.begin(), ashmem_regions_.end(), region); | |
| 522 DCHECK(ashmem_regions_.end() != it); | |
| 523 std::swap(*it, ashmem_regions_.back()); | |
| 524 ashmem_regions_.pop_back(); | |
| 525 } | |
| 526 | |
| 527 } // namespace internal | |
| 528 } // namespace base | |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 1001833005:
Update from https://crrev.com/320343 (Closed)
Base URL: git@github.com:domokit/mojo.git@master