1 /*
2  * Copyright (C) 2012 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #include <stdio.h>
18 #include <unistd.h>
19 #include <sys/mman.h>
20 
21 #include "garbage_collector.h"
22 
23 #include "android-base/stringprintf.h"
24 
25 #include "base/dumpable.h"
26 #include "base/histogram-inl.h"
27 #include "base/logging.h"  // For VLOG_IS_ON.
28 #include "base/mutex-inl.h"
29 #include "base/systrace.h"
30 #include "base/time_utils.h"
31 #include "base/utils.h"
32 #include "gc/accounting/heap_bitmap.h"
33 #include "gc/gc_pause_listener.h"
34 #include "gc/heap.h"
35 #include "gc/space/large_object_space.h"
36 #include "gc/space/space-inl.h"
37 #include "runtime.h"
38 #include "thread-current-inl.h"
39 #include "thread_list.h"
40 
41 namespace art {
42 namespace gc {
43 namespace collector {
44 
Iteration()45 Iteration::Iteration()
46     : duration_ns_(0), timings_("GC iteration timing logger", true, VLOG_IS_ON(heap)) {
47   Reset(kGcCauseBackground, false);  // Reset to some place holder values.
48 }
49 
Reset(GcCause gc_cause,bool clear_soft_references)50 void Iteration::Reset(GcCause gc_cause, bool clear_soft_references) {
51   timings_.Reset();
52   pause_times_.clear();
53   duration_ns_ = 0;
54   bytes_scanned_ = 0;
55   clear_soft_references_ = clear_soft_references;
56   gc_cause_ = gc_cause;
57   freed_ = ObjectBytePair();
58   freed_los_ = ObjectBytePair();
59   freed_bytes_revoke_ = 0;
60 }
61 
GetEstimatedThroughput() const62 uint64_t Iteration::GetEstimatedThroughput() const {
63   // Add 1ms to prevent possible division by 0.
64   return (static_cast<uint64_t>(freed_.bytes) * 1000) / (NsToMs(GetDurationNs()) + 1);
65 }
66 
GarbageCollector(Heap * heap,const std::string & name)67 GarbageCollector::GarbageCollector(Heap* heap, const std::string& name)
68     : heap_(heap),
69       name_(name),
70       pause_histogram_((name_ + " paused").c_str(), kPauseBucketSize, kPauseBucketCount),
71       rss_histogram_((name_ + " peak-rss").c_str(), kMemBucketSize, kMemBucketCount),
72       freed_bytes_histogram_((name_ + " freed-bytes").c_str(), kMemBucketSize, kMemBucketCount),
73       gc_time_histogram_(nullptr),
74       metrics_gc_count_(nullptr),
75       gc_throughput_histogram_(nullptr),
76       gc_tracing_throughput_hist_(nullptr),
77       gc_throughput_avg_(nullptr),
78       gc_tracing_throughput_avg_(nullptr),
79       cumulative_timings_(name),
80       pause_histogram_lock_("pause histogram lock", kDefaultMutexLevel, true),
81       is_transaction_active_(false),
82       are_metrics_initialized_(false) {
83   ResetCumulativeStatistics();
84 }
85 
RegisterPause(uint64_t nano_length)86 void GarbageCollector::RegisterPause(uint64_t nano_length) {
87   GetCurrentIteration()->pause_times_.push_back(nano_length);
88 }
89 
ResetCumulativeStatistics()90 void GarbageCollector::ResetCumulativeStatistics() {
91   cumulative_timings_.Reset();
92   total_thread_cpu_time_ns_ = 0u;
93   total_time_ns_ = 0u;
94   total_freed_objects_ = 0u;
95   total_freed_bytes_ = 0;
96   total_scanned_bytes_ = 0;
97   rss_histogram_.Reset();
98   freed_bytes_histogram_.Reset();
99   MutexLock mu(Thread::Current(), pause_histogram_lock_);
100   pause_histogram_.Reset();
101 }
102 
ExtractRssFromMincore(std::list<std::pair<void *,void * >> * gc_ranges)103 uint64_t GarbageCollector::ExtractRssFromMincore(
104     std::list<std::pair<void*, void*>>* gc_ranges) {
105   uint64_t rss = 0;
106   if (gc_ranges->empty()) {
107     return 0;
108   }
109   // mincore() is linux-specific syscall.
110 #if defined(__linux__)
111   using range_t = std::pair<void*, void*>;
112   // Sort gc_ranges
113   gc_ranges->sort([](const range_t& a, const range_t& b) {
114     return std::less()(a.first, b.first);
115   });
116   // Merge gc_ranges. It's necessary because the kernel may merge contiguous
117   // regions if their properties match. This is sufficient as kernel doesn't
118   // merge those adjoining ranges which differ only in name.
119   size_t vec_len = 0;
120   for (auto it = gc_ranges->begin(); it != gc_ranges->end(); it++) {
121     auto next_it = it;
122     next_it++;
123     while (next_it != gc_ranges->end()) {
124       if (it->second == next_it->first) {
125         it->second = next_it->second;
126         next_it = gc_ranges->erase(next_it);
127       } else {
128         break;
129       }
130     }
131     size_t length = static_cast<uint8_t*>(it->second) - static_cast<uint8_t*>(it->first);
132     // Compute max length for vector allocation later.
133     vec_len = std::max(vec_len, length / kPageSize);
134   }
135   std::unique_ptr<unsigned char[]> vec(new unsigned char[vec_len]);
136   for (const auto it : *gc_ranges) {
137     size_t length = static_cast<uint8_t*>(it.second) - static_cast<uint8_t*>(it.first);
138     if (mincore(it.first, length, vec.get()) == 0) {
139       for (size_t i = 0; i < length / kPageSize; i++) {
140         // Least significant bit represents residency of a page. Other bits are
141         // reserved.
142         rss += vec[i] & 0x1;
143       }
144     } else {
145       LOG(WARNING) << "Call to mincore() on memory range [0x" << std::hex << it.first
146                    << ", 0x" << it.second << std::dec << ") failed: " << strerror(errno);
147     }
148   }
149   rss *= kPageSize;
150   rss_histogram_.AddValue(rss / KB);
151 #endif
152   return rss;
153 }
154 
Run(GcCause gc_cause,bool clear_soft_references)155 void GarbageCollector::Run(GcCause gc_cause, bool clear_soft_references) {
156   ScopedTrace trace(android::base::StringPrintf("%s %s GC", PrettyCause(gc_cause), GetName()));
157   Thread* self = Thread::Current();
158   Runtime* runtime = Runtime::Current();
159   uint64_t start_time = NanoTime();
160   uint64_t thread_cpu_start_time = ThreadCpuNanoTime();
161   GetHeap()->CalculatePreGcWeightedAllocatedBytes();
162   Iteration* current_iteration = GetCurrentIteration();
163   current_iteration->Reset(gc_cause, clear_soft_references);
164   // Note transaction mode is single-threaded and there's no asynchronous GC and this flag doesn't
165   // change in the middle of a GC.
166   is_transaction_active_ = runtime->IsActiveTransaction();
167   RunPhases();  // Run all the GC phases.
168   GetHeap()->CalculatePostGcWeightedAllocatedBytes();
169   // Add the current timings to the cumulative timings.
170   cumulative_timings_.AddLogger(*GetTimings());
171   // Update cumulative statistics with how many bytes the GC iteration freed.
172   total_freed_objects_ += current_iteration->GetFreedObjects() +
173       current_iteration->GetFreedLargeObjects();
174   total_scanned_bytes_ += current_iteration->GetScannedBytes();
175   int64_t freed_bytes = current_iteration->GetFreedBytes() +
176       current_iteration->GetFreedLargeObjectBytes();
177   total_freed_bytes_ += freed_bytes;
178   // Rounding negative freed bytes to 0 as we are not interested in such corner cases.
179   freed_bytes_histogram_.AddValue(std::max<int64_t>(freed_bytes / KB, 0));
180   uint64_t end_time = NanoTime();
181   uint64_t thread_cpu_end_time = ThreadCpuNanoTime();
182   total_thread_cpu_time_ns_ += thread_cpu_end_time - thread_cpu_start_time;
183   uint64_t duration_ns = end_time - start_time;
184   current_iteration->SetDurationNs(duration_ns);
185   if (Locks::mutator_lock_->IsExclusiveHeld(self)) {
186     // The entire GC was paused, clear the fake pauses which might be in the pause times and add
187     // the whole GC duration.
188     current_iteration->pause_times_.clear();
189     RegisterPause(duration_ns);
190   }
191   total_time_ns_ += duration_ns;
192   uint64_t total_pause_time = 0;
193   for (uint64_t pause_time : current_iteration->GetPauseTimes()) {
194     MutexLock mu(self, pause_histogram_lock_);
195     pause_histogram_.AdjustAndAddValue(pause_time);
196     total_pause_time += pause_time;
197   }
198   metrics::ArtMetrics* metrics = runtime->GetMetrics();
199   // Report STW pause time in microseconds.
200   metrics->WorldStopTimeDuringGCAvg()->Add(total_pause_time / 1'000);
201   // Report total collection time of all GCs put together.
202   metrics->TotalGcCollectionTime()->Add(NsToMs(duration_ns));
203   if (are_metrics_initialized_) {
204     metrics_gc_count_->Add(1);
205     // Report GC time in milliseconds.
206     gc_time_histogram_->Add(NsToMs(duration_ns));
207     // Throughput in bytes/s. Add 1us to prevent possible division by 0.
208     uint64_t throughput = (current_iteration->GetScannedBytes() * 1'000'000)
209             / (NsToUs(duration_ns) + 1);
210     // Report in MB/s.
211     throughput /= MB;
212     gc_tracing_throughput_hist_->Add(throughput);
213     gc_tracing_throughput_avg_->Add(throughput);
214 
215     // Report GC throughput in MB/s.
216     throughput = current_iteration->GetEstimatedThroughput() / MB;
217     gc_throughput_histogram_->Add(throughput);
218     gc_throughput_avg_->Add(throughput);
219   }
220   is_transaction_active_ = false;
221 }
222 
SwapBitmaps()223 void GarbageCollector::SwapBitmaps() {
224   TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
225   // Swap the live and mark bitmaps for each alloc space. This is needed since sweep re-swaps
226   // these bitmaps. The bitmap swapping is an optimization so that we do not need to clear the live
227   // bits of dead objects in the live bitmap.
228   const GcType gc_type = GetGcType();
229   for (const auto& space : GetHeap()->GetContinuousSpaces()) {
230     // We never allocate into zygote spaces.
231     if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect ||
232         (gc_type == kGcTypeFull &&
233          space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect)) {
234       if (space->GetLiveBitmap() != nullptr && !space->HasBoundBitmaps()) {
235         CHECK(space->IsContinuousMemMapAllocSpace());
236         space->AsContinuousMemMapAllocSpace()->SwapBitmaps();
237       }
238     }
239   }
240   for (const auto& disc_space : GetHeap()->GetDiscontinuousSpaces()) {
241     disc_space->AsLargeObjectSpace()->SwapBitmaps();
242   }
243 }
244 
GetEstimatedMeanThroughput() const245 uint64_t GarbageCollector::GetEstimatedMeanThroughput() const {
246   // Add 1ms to prevent possible division by 0.
247   return (total_freed_bytes_ * 1000) / (NsToMs(GetCumulativeTimings().GetTotalNs()) + 1);
248 }
249 
ResetMeasurements()250 void GarbageCollector::ResetMeasurements() {
251   {
252     MutexLock mu(Thread::Current(), pause_histogram_lock_);
253     pause_histogram_.Reset();
254   }
255   cumulative_timings_.Reset();
256   rss_histogram_.Reset();
257   freed_bytes_histogram_.Reset();
258   total_thread_cpu_time_ns_ = 0u;
259   total_time_ns_ = 0u;
260   total_freed_objects_ = 0u;
261   total_freed_bytes_ = 0;
262   total_scanned_bytes_ = 0u;
263 }
264 
ScopedPause(GarbageCollector * collector,bool with_reporting)265 GarbageCollector::ScopedPause::ScopedPause(GarbageCollector* collector, bool with_reporting)
266     : start_time_(NanoTime()), collector_(collector), with_reporting_(with_reporting) {
267   Runtime* runtime = Runtime::Current();
268   runtime->GetThreadList()->SuspendAll(__FUNCTION__);
269   if (with_reporting) {
270     GcPauseListener* pause_listener = runtime->GetHeap()->GetGcPauseListener();
271     if (pause_listener != nullptr) {
272       pause_listener->StartPause();
273     }
274   }
275 }
276 
~ScopedPause()277 GarbageCollector::ScopedPause::~ScopedPause() {
278   collector_->RegisterPause(NanoTime() - start_time_);
279   Runtime* runtime = Runtime::Current();
280   if (with_reporting_) {
281     GcPauseListener* pause_listener = runtime->GetHeap()->GetGcPauseListener();
282     if (pause_listener != nullptr) {
283       pause_listener->EndPause();
284     }
285   }
286   runtime->GetThreadList()->ResumeAll();
287 }
288 
289 // Returns the current GC iteration and assocated info.
GetCurrentIteration()290 Iteration* GarbageCollector::GetCurrentIteration() {
291   return heap_->GetCurrentGcIteration();
292 }
GetCurrentIteration() const293 const Iteration* GarbageCollector::GetCurrentIteration() const {
294   return heap_->GetCurrentGcIteration();
295 }
296 
RecordFree(const ObjectBytePair & freed)297 void GarbageCollector::RecordFree(const ObjectBytePair& freed) {
298   GetCurrentIteration()->freed_.Add(freed);
299   heap_->RecordFree(freed.objects, freed.bytes);
300 }
RecordFreeLOS(const ObjectBytePair & freed)301 void GarbageCollector::RecordFreeLOS(const ObjectBytePair& freed) {
302   GetCurrentIteration()->freed_los_.Add(freed);
303   heap_->RecordFree(freed.objects, freed.bytes);
304 }
305 
GetTotalPausedTimeNs()306 uint64_t GarbageCollector::GetTotalPausedTimeNs() {
307   MutexLock mu(Thread::Current(), pause_histogram_lock_);
308   return pause_histogram_.AdjustedSum();
309 }
310 
DumpPerformanceInfo(std::ostream & os)311 void GarbageCollector::DumpPerformanceInfo(std::ostream& os) {
312   const CumulativeLogger& logger = GetCumulativeTimings();
313   const size_t iterations = logger.GetIterations();
314   if (iterations == 0) {
315     return;
316   }
317   os << Dumpable<CumulativeLogger>(logger);
318   const uint64_t total_ns = logger.GetTotalNs();
319   const double seconds = NsToMs(total_ns) / 1000.0;
320   const uint64_t freed_bytes = GetTotalFreedBytes();
321   const uint64_t freed_objects = GetTotalFreedObjects();
322   const uint64_t scanned_bytes = GetTotalScannedBytes();
323   {
324     MutexLock mu(Thread::Current(), pause_histogram_lock_);
325     if (pause_histogram_.SampleSize() > 0) {
326       Histogram<uint64_t>::CumulativeData cumulative_data;
327       pause_histogram_.CreateHistogram(&cumulative_data);
328       pause_histogram_.PrintConfidenceIntervals(os, 0.99, cumulative_data);
329     }
330   }
331 #if defined(__linux__)
332   if (rss_histogram_.SampleSize() > 0) {
333     os << rss_histogram_.Name()
334        << ": Avg: " << PrettySize(rss_histogram_.Mean() * KB)
335        << " Max: " << PrettySize(rss_histogram_.Max() * KB)
336        << " Min: " << PrettySize(rss_histogram_.Min() * KB) << "\n";
337     os << "Peak-rss Histogram: ";
338     rss_histogram_.DumpBins(os);
339     os << "\n";
340   }
341 #endif
342   if (freed_bytes_histogram_.SampleSize() > 0) {
343     os << freed_bytes_histogram_.Name()
344        << ": Avg: " << PrettySize(freed_bytes_histogram_.Mean() * KB)
345        << " Max: " << PrettySize(freed_bytes_histogram_.Max() * KB)
346        << " Min: " << PrettySize(freed_bytes_histogram_.Min() * KB) << "\n";
347     os << "Freed-bytes histogram: ";
348     freed_bytes_histogram_.DumpBins(os);
349     os << "\n";
350   }
351   const double cpu_seconds = NsToMs(GetTotalCpuTime()) / 1000.0;
352   os << GetName() << " total time: " << PrettyDuration(total_ns)
353      << " mean time: " << PrettyDuration(total_ns / iterations) << "\n"
354      << GetName() << " freed: " << freed_objects
355      << " objects with total size " << PrettySize(freed_bytes) << "\n"
356      << GetName() << " throughput: " << freed_objects / seconds << "/s / "
357      << PrettySize(freed_bytes / seconds) << "/s"
358      << "  per cpu-time: "
359      << static_cast<uint64_t>(freed_bytes / cpu_seconds) << "/s / "
360      << PrettySize(freed_bytes / cpu_seconds) << "/s\n"
361      << GetName() << " tracing throughput: "
362      << PrettySize(scanned_bytes / seconds) << "/s "
363      << " per cpu-time: "
364      << PrettySize(scanned_bytes / cpu_seconds) << "/s\n";
365 }
366 
367 }  // namespace collector
368 }  // namespace gc
369 }  // namespace art
370