chrome/browser/chromeos/memory/oom_priority_manager.cc

   1 // Copyright (c) 2012 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 "chrome/browser/chromeos/memory/oom_priority_manager.h"
   6
   7 #include <algorithm>
   8 #include <set>
   9 #include <vector>
  10
  11 #include "ash/multi_profile_uma.h"
  12 #include "ash/session_state_delegate.h"
  13 #include "ash/shell.h"
  14 #include "base/bind.h"
  15 #include "base/bind_helpers.h"
  16 #include "base/command_line.h"
  17 #include "base/metrics/field_trial.h"
  18 #include "base/metrics/histogram.h"
  19 #include "base/process/process.h"
  20 #include "base/strings/string16.h"
  21 #include "base/strings/string_number_conversions.h"
  22 #include "base/strings/string_util.h"
  23 #include "base/strings/utf_string_conversions.h"
  24 #include "base/synchronization/lock.h"
  25 #include "base/threading/thread.h"
  26 #include "base/time/time.h"
  27 #include "build/build_config.h"
  28 #include "chrome/browser/browser_process.h"
  29 #include "chrome/browser/browser_process_platform_part_chromeos.h"
  30 #include "chrome/browser/memory_details.h"
  31 #include "chrome/browser/ui/browser.h"
  32 #include "chrome/browser/ui/browser_iterator.h"
  33 #include "chrome/browser/ui/browser_list.h"
  34 #include "chrome/browser/ui/host_desktop.h"
  35 #include "chrome/browser/ui/tab_contents/tab_contents_iterator.h"
  36 #include "chrome/browser/ui/tabs/tab_strip_model.h"
  37 #include "chrome/browser/ui/tabs/tab_utils.h"
  38 #include "chrome/common/chrome_constants.h"
  39 #include "chrome/common/url_constants.h"
  40 #include "chromeos/chromeos_switches.h"
  41 #include "chromeos/memory/low_memory_listener.h"
  42 #include "content/public/browser/browser_thread.h"
  43 #include "content/public/browser/notification_service.h"
  44 #include "content/public/browser/notification_types.h"
  45 #include "content/public/browser/render_process_host.h"
  46 #include "content/public/browser/render_widget_host.h"
  47 #include "content/public/browser/web_contents.h"
  48 #include "content/public/browser/zygote_host_linux.h"
  49 #include "ui/base/text/bytes_formatting.h"
  50
  51 using base::TimeDelta;
  52 using base::TimeTicks;
  53 using content::BrowserThread;
  54 using content::WebContents;
  55
  56 namespace chromeos {
  57
  58 namespace {
  59
  60 // Record a size in megabytes, over a potential interval up to 32 GB.
  61 #define HISTOGRAM_MEGABYTES(name, sample)                     \
  62     UMA_HISTOGRAM_CUSTOM_COUNTS(name, sample, 1, 32768, 50)
  63
  64 // The default interval in seconds after which to adjust the oom_score_adj
  65 // value.
  66 const int kAdjustmentIntervalSeconds = 10;
  67
  68 // For each period of this length we record a statistic to indicate whether
  69 // or not the user experienced a low memory event. If you change this interval
  70 // you must replace Tabs.Discard.DiscardInLastMinute with a new statistic.
  71 const int kRecentTabDiscardIntervalSeconds = 60;
  72
  73 // If there has been no priority adjustment in this interval, we assume the
  74 // machine was suspended and correct our timing statistics.
  75 const int kSuspendThresholdSeconds = kAdjustmentIntervalSeconds * 4;
  76
  77 // When switching to a new tab the tab's renderer's OOM score needs to be
  78 // updated to reflect its front-most status and protect it from discard.
  79 // However, doing this immediately might slow down tab switch time, so wait
  80 // a little while before doing the adjustment.
  81 const int kFocusedTabScoreAdjustIntervalMs = 500;
  82
  83 // Returns a unique ID for a WebContents.  Do not cast back to a pointer, as
  84 // the WebContents could be deleted if the user closed the tab.
  85 int64 IdFromWebContents(WebContents* web_contents) {
  86   return reinterpret_cast<int64>(web_contents);
  87 }
  88
  89 // Records a statistics |sample| for UMA histogram |name| using a linear
  90 // distribution of buckets.
  91 void RecordLinearHistogram(const std::string& name,
  92                            int sample,
  93                            int maximum,
  94                            size_t bucket_count) {
  95   // Do not use the UMA_HISTOGRAM_... macros here.  They cache the Histogram
  96   // instance and thus only work if |name| is constant.
  97   base::HistogramBase* counter = base::LinearHistogram::FactoryGet(
  98       name,
  99       1,  // Minimum. The 0 bin for underflow is automatically added.
 100       maximum + 1,  // Ensure bucket size of |maximum| / |bucket_count|.
 101       bucket_count + 2,  // Account for the underflow and overflow bins.
 102       base::Histogram::kUmaTargetedHistogramFlag);
 103   counter->Add(sample);
 104 }
 105
 106 }  // namespace
 107
 108 ////////////////////////////////////////////////////////////////////////////////
 109 // OomMemoryDetails logs details about all Chrome processes during an out-of-
 110 // memory event in an attempt to identify the culprit, then discards a tab and
 111 // deletes itself.
 112 class OomMemoryDetails : public MemoryDetails {
 113  public:
 114   OomMemoryDetails();
 115
 116   // MemoryDetails overrides:
 117   virtual void OnDetailsAvailable() OVERRIDE;
 118
 119  private:
 120   virtual ~OomMemoryDetails() {}
 121
 122   TimeTicks start_time_;
 123
 124   DISALLOW_COPY_AND_ASSIGN(OomMemoryDetails);
 125 };
 126
 127 OomMemoryDetails::OomMemoryDetails() {
 128   AddRef();  // Released in OnDetailsAvailable().
 129   start_time_ = TimeTicks::Now();
 130 }
 131
 132 void OomMemoryDetails::OnDetailsAvailable() {
 133   TimeDelta delta = TimeTicks::Now() - start_time_;
 134   // These logs are collected by user feedback reports.  We want them to help
 135   // diagnose user-reported problems with frequently discarded tabs.
 136   std::string log_string = ToLogString();
 137   base::SystemMemoryInfoKB memory;
 138   if (base::GetSystemMemoryInfo(&memory) && memory.gem_size != -1) {
 139     log_string += "Graphics ";
 140     log_string += UTF16ToASCII(ui::FormatBytes(memory.gem_size));
 141   }
 142   LOG(WARNING) << "OOM details (" << delta.InMilliseconds() << " ms):\n"
 143       << log_string;
 144   if (g_browser_process &&
 145       g_browser_process->platform_part()->oom_priority_manager()) {
 146     OomPriorityManager* manager =
 147         g_browser_process->platform_part()->oom_priority_manager();
 148     manager->PurgeBrowserMemory();
 149     manager->DiscardTab();
 150   }
 151   // Delete ourselves so we don't have to worry about OomPriorityManager
 152   // deleting us when we're still working.
 153   Release();
 154 }
 155
 156 ////////////////////////////////////////////////////////////////////////////////
 157 // OomPriorityManager
 158
 159 OomPriorityManager::TabStats::TabStats()
 160   : is_app(false),
 161     is_reloadable_ui(false),
 162     is_playing_audio(false),
 163     is_pinned(false),
 164     is_selected(false),
 165     is_discarded(false),
 166     renderer_handle(0),
 167     tab_contents_id(0) {
 168 }
 169
 170 OomPriorityManager::TabStats::~TabStats() {
 171 }
 172
 173 OomPriorityManager::OomPriorityManager()
 174     : focused_tab_pid_(0),
 175       low_memory_listener_(new LowMemoryListener(this)),
 176       discard_count_(0),
 177       recent_tab_discard_(false) {
 178   registrar_.Add(this,
 179       content::NOTIFICATION_RENDERER_PROCESS_CLOSED,
 180       content::NotificationService::AllBrowserContextsAndSources());
 181   registrar_.Add(this,
 182       content::NOTIFICATION_RENDERER_PROCESS_TERMINATED,
 183       content::NotificationService::AllBrowserContextsAndSources());
 184   registrar_.Add(this,
 185       content::NOTIFICATION_RENDER_WIDGET_VISIBILITY_CHANGED,
 186       content::NotificationService::AllBrowserContextsAndSources());
 187 }
 188
 189 OomPriorityManager::~OomPriorityManager() {
 190   Stop();
 191 }
 192
 193 void OomPriorityManager::Start() {
 194   if (!timer_.IsRunning()) {
 195     timer_.Start(FROM_HERE,
 196                  TimeDelta::FromSeconds(kAdjustmentIntervalSeconds),
 197                  this,
 198                  &OomPriorityManager::AdjustOomPriorities);
 199   }
 200   if (!recent_tab_discard_timer_.IsRunning()) {
 201     recent_tab_discard_timer_.Start(
 202         FROM_HERE,
 203         TimeDelta::FromSeconds(kRecentTabDiscardIntervalSeconds),
 204         this,
 205         &OomPriorityManager::RecordRecentTabDiscard);
 206   }
 207   if (low_memory_listener_.get())
 208     low_memory_listener_->Start();
 209   start_time_ = TimeTicks::Now();
 210 }
 211
 212 void OomPriorityManager::Stop() {
 213   timer_.Stop();
 214   recent_tab_discard_timer_.Stop();
 215   if (low_memory_listener_.get())
 216     low_memory_listener_->Stop();
 217 }
 218
 219 std::vector<base::string16> OomPriorityManager::GetTabTitles() {
 220   TabStatsList stats = GetTabStatsOnUIThread();
 221   base::AutoLock pid_to_oom_score_autolock(pid_to_oom_score_lock_);
 222   std::vector<base::string16> titles;
 223   titles.reserve(stats.size());
 224   TabStatsList::iterator it = stats.begin();
 225   for ( ; it != stats.end(); ++it) {
 226     base::string16 str;
 227     str.reserve(4096);
 228     int score = pid_to_oom_score_[it->renderer_handle];
 229     str += base::IntToString16(score);
 230     str += base::ASCIIToUTF16(" - ");
 231     str += it->title;
 232     str += base::ASCIIToUTF16(it->is_app ? " app" : "");
 233     str += base::ASCIIToUTF16(it->is_reloadable_ui ? " reloadable_ui" : "");
 234     str += base::ASCIIToUTF16(it->is_playing_audio ? " playing_audio" : "");
 235     str += base::ASCIIToUTF16(it->is_pinned ? " pinned" : "");
 236     str += base::ASCIIToUTF16(it->is_discarded ? " discarded" : "");
 237     titles.push_back(str);
 238   }
 239   return titles;
 240 }
 241
 242 // TODO(jamescook): This should consider tabs with references to other tabs,
 243 // such as tabs created with JavaScript window.open().  We might want to
 244 // discard the entire set together, or use that in the priority computation.
 245 bool OomPriorityManager::DiscardTab() {
 246   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 247   TabStatsList stats = GetTabStatsOnUIThread();
 248   if (stats.empty())
 249     return false;
 250   // Loop until we find a non-discarded tab to kill.
 251   for (TabStatsList::const_reverse_iterator stats_rit = stats.rbegin();
 252        stats_rit != stats.rend();
 253        ++stats_rit) {
 254     int64 least_important_tab_id = stats_rit->tab_contents_id;
 255     if (DiscardTabById(least_important_tab_id))
 256       return true;
 257   }
 258   return false;
 259 }
 260
 261 void OomPriorityManager::LogMemoryAndDiscardTab() {
 262   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 263   // Deletes itself upon completion.
 264   OomMemoryDetails* details = new OomMemoryDetails();
 265   details->StartFetch(MemoryDetails::SKIP_USER_METRICS);
 266 }
 267
 268 ///////////////////////////////////////////////////////////////////////////////
 269 // OomPriorityManager, private:
 270
 271 // static
 272 bool OomPriorityManager::IsReloadableUI(const GURL& url) {
 273   // There are many chrome:// UI URLs, but only look for the ones that users
 274   // are likely to have open. Most of the benefit is the from NTP URL.
 275   const char* kReloadableUrlPrefixes[] = {
 276       chrome::kChromeUIDownloadsURL,
 277       chrome::kChromeUIHistoryURL,
 278       chrome::kChromeUINewTabURL,
 279       chrome::kChromeUISettingsURL,
 280   };
 281   // Prefix-match against the table above. Use strncmp to avoid allocating
 282   // memory to convert the URL prefix constants into std::strings.
 283   for (size_t i = 0; i < arraysize(kReloadableUrlPrefixes); ++i) {
 284     if (!strncmp(url.spec().c_str(),
 285                  kReloadableUrlPrefixes[i],
 286                  strlen(kReloadableUrlPrefixes[i])))
 287       return true;
 288   }
 289   return false;
 290 }
 291
 292 bool OomPriorityManager::DiscardTabById(int64 target_web_contents_id) {
 293   for (chrome::BrowserIterator it; !it.done(); it.Next()) {
 294     Browser* browser = *it;
 295     TabStripModel* model = browser->tab_strip_model();
 296     for (int idx = 0; idx < model->count(); idx++) {
 297       // Can't discard tabs that are already discarded or active.
 298       if (model->IsTabDiscarded(idx) || (model->active_index() == idx))
 299         continue;
 300       WebContents* web_contents = model->GetWebContentsAt(idx);
 301       int64 web_contents_id = IdFromWebContents(web_contents);
 302       if (web_contents_id == target_web_contents_id) {
 303         LOG(WARNING) << "Discarding tab " << idx
 304                      << " id " << target_web_contents_id;
 305         // Record statistics before discarding because we want to capture the
 306         // memory state that lead to the discard.
 307         RecordDiscardStatistics();
 308         model->DiscardWebContentsAt(idx);
 309         recent_tab_discard_ = true;
 310         return true;
 311       }
 312     }
 313   }
 314   return false;
 315 }
 316
 317 void OomPriorityManager::RecordDiscardStatistics() {
 318   // Record a raw count so we can compare to discard reloads.
 319   discard_count_++;
 320   UMA_HISTOGRAM_CUSTOM_COUNTS(
 321       "Tabs.Discard.DiscardCount", discard_count_, 1, 1000, 50);
 322
 323   // TODO(jamescook): Maybe incorporate extension count?
 324   UMA_HISTOGRAM_CUSTOM_COUNTS(
 325       "Tabs.Discard.TabCount", GetTabCount(), 1, 100, 50);
 326
 327   // Record the discarded tab in relation to the amount of simultaneously
 328   // logged in users.
 329   ash::MultiProfileUMA::RecordDiscardedTab(
 330       ash::Shell::GetInstance()->session_state_delegate()->
 331           NumberOfLoggedInUsers());
 332
 333   // TODO(jamescook): If the time stats prove too noisy, then divide up users
 334   // based on how heavily they use Chrome using tab count as a proxy.
 335   // Bin into <= 1, <= 2, <= 4, <= 8, etc.
 336   if (last_discard_time_.is_null()) {
 337     // This is the first discard this session.
 338     TimeDelta interval = TimeTicks::Now() - start_time_;
 339     int interval_seconds = static_cast<int>(interval.InSeconds());
 340     // Record time in seconds over an interval of approximately 1 day.
 341     UMA_HISTOGRAM_CUSTOM_COUNTS(
 342         "Tabs.Discard.InitialTime2", interval_seconds, 1, 100000, 50);
 343   } else {
 344     // Not the first discard, so compute time since last discard.
 345     TimeDelta interval = TimeTicks::Now() - last_discard_time_;
 346     int interval_ms = static_cast<int>(interval.InMilliseconds());
 347     // Record time in milliseconds over an interval of approximately 1 day.
 348     // Start at 100 ms to get extra resolution in the target 750 ms range.
 349     UMA_HISTOGRAM_CUSTOM_COUNTS(
 350         "Tabs.Discard.IntervalTime2", interval_ms, 100, 100000 * 1000, 50);
 351   }
 352   // Record Chrome's concept of system memory usage at the time of the discard.
 353   base::SystemMemoryInfoKB memory;
 354   if (base::GetSystemMemoryInfo(&memory)) {
 355     // TODO(jamescook): Remove this after R25 is deployed to stable. It does
 356     // not have sufficient resolution in the 2-4 GB range and does not properly
 357     // account for graphics memory on ARM. Replace with MemAllocatedMB below.
 358     int mem_anonymous_mb = (memory.active_anon + memory.inactive_anon) / 1024;
 359     HISTOGRAM_MEGABYTES("Tabs.Discard.MemAnonymousMB", mem_anonymous_mb);
 360
 361     // Record graphics GEM object size in a histogram with 50 MB buckets.
 362     int mem_graphics_gem_mb = 0;
 363     if (memory.gem_size != -1)
 364       mem_graphics_gem_mb = memory.gem_size / 1024 / 1024;
 365     RecordLinearHistogram(
 366         "Tabs.Discard.MemGraphicsMB", mem_graphics_gem_mb, 2500, 50);
 367
 368     // Record shared memory (used by renderer/GPU buffers).
 369     int mem_shmem_mb = memory.shmem / 1024;
 370     RecordLinearHistogram("Tabs.Discard.MemShmemMB", mem_shmem_mb, 2500, 50);
 371
 372     // On Intel, graphics objects are in anonymous pages, but on ARM they are
 373     // not. For a total "allocated count" add in graphics pages on ARM.
 374     int mem_allocated_mb = mem_anonymous_mb;
 375 #if defined(ARCH_CPU_ARM_FAMILY)
 376     mem_allocated_mb += mem_graphics_gem_mb;
 377 #endif
 378     UMA_HISTOGRAM_CUSTOM_COUNTS(
 379         "Tabs.Discard.MemAllocatedMB", mem_allocated_mb, 256, 32768, 50);
 380
 381     int mem_available_mb =
 382         (memory.active_file + memory.inactive_file + memory.free) / 1024;
 383     HISTOGRAM_MEGABYTES("Tabs.Discard.MemAvailableMB", mem_available_mb);
 384   }
 385   // Set up to record the next interval.
 386   last_discard_time_ = TimeTicks::Now();
 387 }
 388
 389 void OomPriorityManager::RecordRecentTabDiscard() {
 390   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 391   // If we change the interval we need to change the histogram name.
 392   UMA_HISTOGRAM_BOOLEAN("Tabs.Discard.DiscardInLastMinute",
 393                         recent_tab_discard_);
 394   // Reset for the next interval.
 395   recent_tab_discard_ = false;
 396 }
 397
 398 void OomPriorityManager::PurgeBrowserMemory() {
 399   // Based on experimental evidence, attempts to free memory from renderers
 400   // have been too slow to use in OOM situations (V8 garbage collection) or
 401   // do not lead to persistent decreased usage (image/bitmap caches). This
 402   // function therefore only targets large blocks of memory in the browser.
 403   for (TabContentsIterator it; !it.done(); it.Next()) {
 404     WebContents* web_contents = *it;
 405     // Screenshots can consume ~5 MB per web contents for platforms that do
 406     // touch back/forward.
 407     web_contents->GetController().ClearAllScreenshots();
 408   }
 409   // TODO(jamescook): Are there other things we could flush? Drive metadata?
 410 }
 411
 412 int OomPriorityManager::GetTabCount() const {
 413   int tab_count = 0;
 414   for (chrome::BrowserIterator it; !it.done(); it.Next())
 415     tab_count += it->tab_strip_model()->count();
 416   return tab_count;
 417 }
 418
 419 // Returns true if |first| is considered less desirable to be killed
 420 // than |second|.
 421 bool OomPriorityManager::CompareTabStats(TabStats first,
 422                                          TabStats second) {
 423   // Being currently selected is most important to protect.
 424   if (first.is_selected != second.is_selected)
 425     return first.is_selected;
 426
 427   // Tab with internal web UI like NTP or Settings are good choices to discard,
 428   // so protect non-Web UI and let the other conditionals finish the sort.
 429   if (first.is_reloadable_ui != second.is_reloadable_ui)
 430     return !first.is_reloadable_ui;
 431
 432   // Being pinned is important to protect.
 433   if (first.is_pinned != second.is_pinned)
 434     return first.is_pinned;
 435
 436   // Being an app is important too, as you're the only visible surface in the
 437   // window and we don't want to discard that.
 438   if (first.is_app != second.is_app)
 439     return first.is_app;
 440
 441   // Protect streaming audio and video conferencing tabs.
 442   if (first.is_playing_audio != second.is_playing_audio)
 443     return first.is_playing_audio;
 444
 445   // TODO(jamescook): Incorporate sudden_termination_allowed into the sort
 446   // order.  We don't do this now because pages with unload handlers set
 447   // sudden_termination_allowed false, and that covers too many common pages
 448   // with ad networks and statistics scripts.  Ideally we would like to check
 449   // for beforeUnload handlers, which are likely to present a dialog asking
 450   // if the user wants to discard state.  crbug.com/123049
 451
 452   // Being more recently selected is more important.
 453   return first.last_selected > second.last_selected;
 454 }
 455
 456 void OomPriorityManager::AdjustFocusedTabScoreOnFileThread() {
 457   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 458   base::AutoLock pid_to_oom_score_autolock(pid_to_oom_score_lock_);
 459   content::ZygoteHost::GetInstance()->AdjustRendererOOMScore(
 460       focused_tab_pid_, chrome::kLowestRendererOomScore);
 461   pid_to_oom_score_[focused_tab_pid_] = chrome::kLowestRendererOomScore;
 462 }
 463
 464 void OomPriorityManager::OnFocusTabScoreAdjustmentTimeout() {
 465   BrowserThread::PostTask(
 466       BrowserThread::FILE, FROM_HERE,
 467       base::Bind(&OomPriorityManager::AdjustFocusedTabScoreOnFileThread,
 468                  base::Unretained(this)));
 469 }
 470
 471 void OomPriorityManager::Observe(int type,
 472                                  const content::NotificationSource& source,
 473                                  const content::NotificationDetails& details) {
 474   base::ProcessHandle handle = 0;
 475   base::AutoLock pid_to_oom_score_autolock(pid_to_oom_score_lock_);
 476   switch (type) {
 477     case content::NOTIFICATION_RENDERER_PROCESS_CLOSED: {
 478       handle =
 479           content::Details<content::RenderProcessHost::RendererClosedDetails>(
 480               details)->handle;
 481       pid_to_oom_score_.erase(handle);
 482       break;
 483     }
 484     case content::NOTIFICATION_RENDERER_PROCESS_TERMINATED: {
 485       handle = content::Source<content::RenderProcessHost>(source)->
 486           GetHandle();
 487       pid_to_oom_score_.erase(handle);
 488       break;
 489     }
 490     case content::NOTIFICATION_RENDER_WIDGET_VISIBILITY_CHANGED: {
 491       bool visible = *content::Details<bool>(details).ptr();
 492       if (visible) {
 493         focused_tab_pid_ =
 494             content::Source<content::RenderWidgetHost>(source).ptr()->
 495             GetProcess()->GetHandle();
 496
 497         // If the currently focused tab already has a lower score, do not
 498         // set it. This can happen in case the newly focused tab is script
 499         // connected to the previous tab.
 500         ProcessScoreMap::iterator it;
 501         it = pid_to_oom_score_.find(focused_tab_pid_);
 502         if (it == pid_to_oom_score_.end()
 503             || it->second != chrome::kLowestRendererOomScore) {
 504           // By starting a timer we guarantee that the tab is focused for
 505           // certain amount of time. Secondly, it also does not add overhead
 506           // to the tab switching time.
 507           if (focus_tab_score_adjust_timer_.IsRunning())
 508             focus_tab_score_adjust_timer_.Reset();
 509           else
 510             focus_tab_score_adjust_timer_.Start(FROM_HERE,
 511               TimeDelta::FromMilliseconds(kFocusedTabScoreAdjustIntervalMs),
 512               this, &OomPriorityManager::OnFocusTabScoreAdjustmentTimeout);
 513         }
 514       }
 515       break;
 516     }
 517     default:
 518       NOTREACHED() << L"Received unexpected notification";
 519       break;
 520   }
 521 }
 522
 523 // Here we collect most of the information we need to sort the
 524 // existing renderers in priority order, and hand out oom_score_adj
 525 // scores based on that sort order.
 526 //
 527 // Things we need to collect on the browser thread (because
 528 // TabStripModel isn't thread safe):
 529 // 1) whether or not a tab is pinned
 530 // 2) last time a tab was selected
 531 // 3) is the tab currently selected
 532 void OomPriorityManager::AdjustOomPriorities() {
 533   if (BrowserList::GetInstance(chrome::HOST_DESKTOP_TYPE_ASH)->empty())
 534     return;
 535
 536   // Check for a discontinuity in time caused by the machine being suspended.
 537   if (!last_adjust_time_.is_null()) {
 538     TimeDelta suspend_time = TimeTicks::Now() - last_adjust_time_;
 539     if (suspend_time.InSeconds() > kSuspendThresholdSeconds) {
 540       // We were probably suspended, move our event timers forward in time so
 541       // when we subtract them out later we are counting "uptime".
 542       start_time_ += suspend_time;
 543       if (!last_discard_time_.is_null())
 544         last_discard_time_ += suspend_time;
 545     }
 546   }
 547   last_adjust_time_ = TimeTicks::Now();
 548
 549   TabStatsList stats_list = GetTabStatsOnUIThread();
 550   BrowserThread::PostTask(
 551       BrowserThread::FILE, FROM_HERE,
 552       base::Bind(&OomPriorityManager::AdjustOomPrioritiesOnFileThread,
 553                  base::Unretained(this), stats_list));
 554 }
 555
 556 OomPriorityManager::TabStatsList OomPriorityManager::GetTabStatsOnUIThread() {
 557   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 558   TabStatsList stats_list;
 559   stats_list.reserve(32);  // 99% of users have < 30 tabs open
 560   bool browser_active = true;
 561   const BrowserList* ash_browser_list =
 562       BrowserList::GetInstance(chrome::HOST_DESKTOP_TYPE_ASH);
 563   for (BrowserList::const_reverse_iterator browser_iterator =
 564            ash_browser_list->begin_last_active();
 565        browser_iterator != ash_browser_list->end_last_active();
 566        ++browser_iterator) {
 567     Browser* browser = *browser_iterator;
 568     bool is_browser_for_app = browser->is_app();
 569     const TabStripModel* model = browser->tab_strip_model();
 570     for (int i = 0; i < model->count(); i++) {
 571       WebContents* contents = model->GetWebContentsAt(i);
 572       if (!contents->IsCrashed()) {
 573         TabStats stats;
 574         stats.is_app = is_browser_for_app;
 575         stats.is_reloadable_ui =
 576             IsReloadableUI(contents->GetLastCommittedURL());
 577         stats.is_playing_audio = chrome::IsPlayingAudio(contents);
 578         stats.is_pinned = model->IsTabPinned(i);
 579         stats.is_selected = browser_active && model->IsTabSelected(i);
 580         stats.is_discarded = model->IsTabDiscarded(i);
 581         stats.last_selected = contents->GetLastSelectedTime();
 582         stats.renderer_handle = contents->GetRenderProcessHost()->GetHandle();
 583         stats.title = contents->GetTitle();
 584         stats.tab_contents_id = IdFromWebContents(contents);
 585         stats_list.push_back(stats);
 586       }
 587     }
 588     // We process the active browser window in the first iteration.
 589     browser_active = false;
 590   }
 591   // Sort the data we collected so that least desirable to be
 592   // killed is first, most desirable is last.
 593   std::sort(stats_list.begin(), stats_list.end(), CompareTabStats);
 594   return stats_list;
 595 }
 596
 597 void OomPriorityManager::AdjustOomPrioritiesOnFileThread(
 598     TabStatsList stats_list) {
 599   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 600   base::AutoLock pid_to_oom_score_autolock(pid_to_oom_score_lock_);
 601
 602   // Now we assign priorities based on the sorted list.  We're
 603   // assigning priorities in the range of kLowestRendererOomScore to
 604   // kHighestRendererOomScore (defined in chrome_constants.h).
 605   // oom_score_adj takes values from -1000 to 1000.  Negative values
 606   // are reserved for system processes, and we want to give some room
 607   // below the range we're using to allow for things that want to be
 608   // above the renderers in priority, so the defined range gives us
 609   // some variation in priority without taking up the whole range.  In
 610   // the end, however, it's a pretty arbitrary range to use.  Higher
 611   // values are more likely to be killed by the OOM killer.
 612   //
 613   // We also remove any duplicate PIDs, leaving the most important
 614   // (least likely to be killed) of the duplicates, so that a
 615   // particular renderer process takes on the oom_score_adj of the
 616   // least likely tab to be killed.
 617   const int kPriorityRange = chrome::kHighestRendererOomScore -
 618                              chrome::kLowestRendererOomScore;
 619   float priority_increment =
 620       static_cast<float>(kPriorityRange) / stats_list.size();
 621   float priority = chrome::kLowestRendererOomScore;
 622   std::set<base::ProcessHandle> already_seen;
 623   int score = 0;
 624   ProcessScoreMap::iterator it;
 625   for (TabStatsList::iterator iterator = stats_list.begin();
 626        iterator != stats_list.end(); ++iterator) {
 627     // stats_list also contains discarded tab stat. If renderer_handler is zero,
 628     // we don't need to adjust oom_score.
 629     if (iterator->renderer_handle == 0)
 630       continue;
 631     if (already_seen.find(iterator->renderer_handle) == already_seen.end()) {
 632       already_seen.insert(iterator->renderer_handle);
 633       // If a process has the same score as the newly calculated value,
 634       // do not set it.
 635       score = static_cast<int>(priority + 0.5f);
 636       it = pid_to_oom_score_.find(iterator->renderer_handle);
 637       if (it == pid_to_oom_score_.end() || it->second != score) {
 638         content::ZygoteHost::GetInstance()->AdjustRendererOOMScore(
 639             iterator->renderer_handle, score);
 640         pid_to_oom_score_[iterator->renderer_handle] = score;
 641       }
 642       priority += priority_increment;
 643     }
 644   }
 645 }
 646
 647 void OomPriorityManager::OnMemoryLow() {
 648   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 649   LogMemoryAndDiscardTab();
 650 }
 651
 652 }  // namespace chromeos