base/memory/discardable_memory_mach.cc

   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_mach.h"
   6
   7 #include <mach/mach.h>
   8
   9 #include "base/basictypes.h"
  10 #include "base/compiler_specific.h"
  11 #include "base/lazy_instance.h"
  12 #include "base/logging.h"
  13 #include "base/mac/mach_logging.h"
  14
  15 namespace base {
  16 namespace {
  17
  18 // For Mach, have the DiscardableMemoryManager trigger userspace eviction when
  19 // address space usage gets too high (e.g. 512 MBytes).
  20 const size_t kMachMemoryLimit = 512 * 1024 * 1024;
  21
  22 // internal::DiscardableMemoryManager has an explicit constructor that takes
  23 // a number of memory limit parameters. The LeakyLazyInstanceTraits doesn't
  24 // handle the case. Thus, we need our own class here.
  25 struct DiscardableMemoryManagerLazyInstanceTraits {
  26   // Leaky as discardable memory clients can use this after the exit handler
  27   // has been called.
  28   static const bool kRegisterOnExit = false;
  29 #ifndef NDEBUG
  30   static const bool kAllowedToAccessOnNonjoinableThread = true;
  31 #endif
  32
  33   static internal::DiscardableMemoryManager* New(void* instance) {
  34     return new (instance) internal::DiscardableMemoryManager(
  35         kMachMemoryLimit, kMachMemoryLimit, TimeDelta::Max());
  36   }
  37   static void Delete(internal::DiscardableMemoryManager* instance) {
  38     instance->~DiscardableMemoryManager();
  39   }
  40 };
  41
  42 LazyInstance<internal::DiscardableMemoryManager,
  43              DiscardableMemoryManagerLazyInstanceTraits>
  44     g_manager = LAZY_INSTANCE_INITIALIZER;
  45
  46 // The VM subsystem allows tagging of memory and 240-255 is reserved for
  47 // application use (see mach/vm_statistics.h). Pick 252 (after chromium's atomic
  48 // weight of ~52).
  49 const int kDiscardableMemoryTag = VM_MAKE_TAG(252);
  50
  51 }  // namespace
  52
  53 namespace internal {
  54
  55 DiscardableMemoryMach::DiscardableMemoryMach(size_t bytes)
  56     : memory_(0, 0), bytes_(mach_vm_round_page(bytes)), is_locked_(false) {
  57   g_manager.Pointer()->Register(this, bytes);
  58 }
  59
  60 DiscardableMemoryMach::~DiscardableMemoryMach() {
  61   if (is_locked_)
  62     Unlock();
  63   g_manager.Pointer()->Unregister(this);
  64 }
  65
  66 // static
  67 void DiscardableMemoryMach::PurgeForTesting() {
  68   int state = 0;
  69   vm_purgable_control(mach_task_self(), 0, VM_PURGABLE_PURGE_ALL, &state);
  70 }
  71
  72 bool DiscardableMemoryMach::Initialize() {
  73   return Lock() != DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
  74 }
  75
  76 DiscardableMemoryLockStatus DiscardableMemoryMach::Lock() {
  77   DCHECK(!is_locked_);
  78
  79   bool purged = false;
  80   if (!g_manager.Pointer()->AcquireLock(this, &purged))
  81     return DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
  82
  83   is_locked_ = true;
  84   return purged ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
  85                 : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
  86 }
  87
  88 void DiscardableMemoryMach::Unlock() {
  89   DCHECK(is_locked_);
  90   g_manager.Pointer()->ReleaseLock(this);
  91   is_locked_ = false;
  92 }
  93
  94 void* DiscardableMemoryMach::Memory() const {
  95   DCHECK(is_locked_);
  96   return reinterpret_cast<void*>(memory_.address());
  97 }
  98
  99 bool DiscardableMemoryMach::AllocateAndAcquireLock() {
 100   kern_return_t ret;
 101   bool persistent;
 102   if (!memory_.size()) {
 103     vm_address_t address = 0;
 104     ret = vm_allocate(
 105         mach_task_self(),
 106         &address,
 107         bytes_,
 108         VM_FLAGS_ANYWHERE | VM_FLAGS_PURGABLE | kDiscardableMemoryTag);
 109     MACH_CHECK(ret == KERN_SUCCESS, ret) << "vm_allocate";
 110     memory_.reset(address, bytes_);
 111
 112     // When making a fresh allocation, it's impossible for |persistent| to
 113     // be true.
 114     persistent = false;
 115   } else {
 116     // |persistent| will be reset to false below if appropriate, but when
 117     // reusing an existing allocation, it's possible for it to be true.
 118     persistent = true;
 119
 120 #if !defined(NDEBUG)
 121     ret = vm_protect(mach_task_self(),
 122                      memory_.address(),
 123                      memory_.size(),
 124                      FALSE,
 125                      VM_PROT_DEFAULT);
 126     MACH_DCHECK(ret == KERN_SUCCESS, ret) << "vm_protect";
 127 #endif
 128   }
 129
 130   int state = VM_PURGABLE_NONVOLATILE;
 131   ret = vm_purgable_control(
 132       mach_task_self(), memory_.address(), VM_PURGABLE_SET_STATE, &state);
 133   MACH_CHECK(ret == KERN_SUCCESS, ret) << "vm_purgable_control";
 134   if (state & VM_PURGABLE_EMPTY)
 135     persistent = false;
 136
 137   return persistent;
 138 }
 139
 140 void DiscardableMemoryMach::ReleaseLock() {
 141   int state = VM_PURGABLE_VOLATILE | VM_VOLATILE_GROUP_DEFAULT;
 142   kern_return_t ret = vm_purgable_control(
 143       mach_task_self(), memory_.address(), VM_PURGABLE_SET_STATE, &state);
 144   MACH_CHECK(ret == KERN_SUCCESS, ret) << "vm_purgable_control";
 145
 146 #if !defined(NDEBUG)
 147   ret = vm_protect(
 148       mach_task_self(), memory_.address(), memory_.size(), FALSE, VM_PROT_NONE);
 149   MACH_DCHECK(ret == KERN_SUCCESS, ret) << "vm_protect";
 150 #endif
 151 }
 152
 153 void DiscardableMemoryMach::Purge() {
 154   memory_.reset();
 155 }
 156
 157 bool DiscardableMemoryMach::IsMemoryResident() const {
 158   return true;
 159 }
 160
 161 }  // namespace internal
 162 }  // namespace base