The Tor Browser: js/src/gc/Statistics.cpp@b8a032363ba2 (annotated)

js/src/gc/Statistics.cpp@b8a032363ba2 (annotated)

js/src/gc/Statistics.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "gc/Statistics.h"
 #include "mozilla/PodOperations.h"
 #include <ctype.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include "jscrashreport.h"
 #include "jsprf.h"
 #include "jsutil.h"
 #include "prmjtime.h"
 #include "gc/Memory.h"
 #include "vm/Runtime.h"
 using namespace js;
 using namespace js::gcstats;
 using mozilla::PodArrayZero;
 /* Except for the first and last, slices of less than 42ms are not reported. */
 static const int64_t SLICE_MIN_REPORT_TIME = 42 * PRMJ_USEC_PER_MSEC;
 class gcstats::StatisticsSerializer
 {
     typedef Vector<char, 128, SystemAllocPolicy> CharBuffer;
     CharBuffer buf_;
     bool asJSON_;
     bool needComma_;
     bool oom_;
     static const int MaxFieldValueLength = 128;
   public:
     enum Mode {
         AsJSON = true,
         AsText = false
     };
     StatisticsSerializer(Mode asJSON)
       : buf_(), asJSON_(asJSON), needComma_(false), oom_(false)
     {}
     bool isJSON() { return asJSON_; }
     bool isOOM() { return oom_; }
     void endLine() {
         if (!asJSON_) {
             p("\n");
             needComma_ = false;
         }
     }
     void extra(const char *str) {
         if (!asJSON_) {
             needComma_ = false;
             p(str);
         }
     }
     void appendString(const char *name, const char *value) {
         put(name, value, "", true);
     }
     void appendNumber(const char *name, const char *vfmt, const char *units, ...) {
         va_list va;
         va_start(va, units);
         append(name, vfmt, va, units);
         va_end(va);
     }
     void appendDecimal(const char *name, const char *units, double d) {
         if (d < 0)
             d = 0;
         if (asJSON_)
             appendNumber(name, "%d.%d", units, (int)d, (int)(d * 10.) % 10);
         else
             appendNumber(name, "%.1f", units, d);
     }
     void appendIfNonzeroMS(const char *name, double v) {
         if (asJSON_ || v >= 0.1)
             appendDecimal(name, "ms", v);
     }
     void beginObject(const char *name) {
         if (needComma_)
             pJSON(", ");
         if (asJSON_ && name) {
             putKey(name);
             pJSON(": ");
         }
         pJSON("{");
         needComma_ = false;
     }
     void endObject() {
         needComma_ = false;
         pJSON("}");
         needComma_ = true;
     }
     void beginArray(const char *name) {
         if (needComma_)
             pJSON(", ");
         if (asJSON_)
             putKey(name);
         pJSON(": [");
         needComma_ = false;
     }
     void endArray() {
         needComma_ = false;
         pJSON("]");
         needComma_ = true;
     }
     jschar *finishJSString() {
         char *buf = finishCString();
         if (!buf)
             return nullptr;
         size_t nchars = strlen(buf);
         jschar *out = js_pod_malloc<jschar>(nchars + 1);
         if (!out) {
             oom_ = true;
             js_free(buf);
             return nullptr;
         }
         InflateStringToBuffer(buf, nchars, out);
         js_free(buf);
         out[nchars] = 0;
         return out;
     }
     char *finishCString() {
         if (oom_)
             return nullptr;
         buf_.append('\0');
         char *buf = buf_.extractRawBuffer();
         if (!buf)
             oom_ = true;
         return buf;
     }
   private:
     void append(const char *name, const char *vfmt,
                 va_list va, const char *units)
     {
         char val[MaxFieldValueLength];
         JS_vsnprintf(val, MaxFieldValueLength, vfmt, va);
         put(name, val, units, false);
     }
     void p(const char *cstr) {
         if (oom_)
             return;
         if (!buf_.append(cstr, strlen(cstr)))
             oom_ = true;
     }
     void p(const char c) {
         if (oom_)
             return;
         if (!buf_.append(c))
             oom_ = true;
     }
     void pJSON(const char *str) {
         if (asJSON_)
             p(str);
     }
     void put(const char *name, const char *val, const char *units, bool valueIsQuoted) {
         if (needComma_)
             p(", ");
         needComma_ = true;
         putKey(name);
         p(": ");
         if (valueIsQuoted)
             putQuoted(val);
         else
             p(val);
         if (!asJSON_)
             p(units);
     }
     void putQuoted(const char *str) {
         pJSON("\"");
         p(str);
         pJSON("\"");
     }
     void putKey(const char *str) {
         if (!asJSON_) {
             p(str);
             return;
         }
         p("\"");
         const char *c = str;
         while (*c) {
             if (*c == ' ' || *c == '\t')
                 p('_');
             else if (isupper(*c))
                 p(tolower(*c));
             else if (*c == '+')
                 p("added_");
             else if (*c == '-')
                 p("removed_");
             else if (*c != '(' && *c != ')')
                 p(*c);
             c++;
         }
         p("\"");
     }
 };
 /*
  * If this fails, then you can either delete this assertion and allow all
  * larger-numbered reasons to pile up in the last telemetry bucket, or switch
  * to GC_REASON_3 and bump the max value.
  */
 JS_STATIC_ASSERT(JS::gcreason::NUM_TELEMETRY_REASONS >= JS::gcreason::NUM_REASONS);
 const char *
 js::gcstats::ExplainReason(JS::gcreason::Reason reason)
 {
     switch (reason) {
 #define SWITCH_REASON(name)                     \
         case JS::gcreason::name:                    \
           return #name;
         GCREASONS(SWITCH_REASON)
         default:
           MOZ_ASSUME_UNREACHABLE("bad GC reason");
 #undef SWITCH_REASON
     }
 }
 static double
 t(int64_t t)
 {
     return double(t) / PRMJ_USEC_PER_MSEC;
 }
 struct PhaseInfo
 {
     Phase index;
     const char *name;
     Phase parent;
 };
 static const Phase PHASE_NO_PARENT = PHASE_LIMIT;
 static const PhaseInfo phases[] = {
     { PHASE_GC_BEGIN, "Begin Callback", PHASE_NO_PARENT },
     { PHASE_WAIT_BACKGROUND_THREAD, "Wait Background Thread", PHASE_NO_PARENT },
     { PHASE_MARK_DISCARD_CODE, "Mark Discard Code", PHASE_NO_PARENT },
     { PHASE_PURGE, "Purge", PHASE_NO_PARENT },
     { PHASE_MARK, "Mark", PHASE_NO_PARENT },
     { PHASE_MARK_ROOTS, "Mark Roots", PHASE_MARK },
     { PHASE_MARK_DELAYED, "Mark Delayed", PHASE_MARK },
     { PHASE_SWEEP, "Sweep", PHASE_NO_PARENT },
     { PHASE_SWEEP_MARK, "Mark During Sweeping", PHASE_SWEEP },
     { PHASE_SWEEP_MARK_TYPES, "Mark Types During Sweeping", PHASE_SWEEP_MARK },
     { PHASE_SWEEP_MARK_INCOMING_BLACK, "Mark Incoming Black Pointers", PHASE_SWEEP_MARK },
     { PHASE_SWEEP_MARK_WEAK, "Mark Weak", PHASE_SWEEP_MARK },
     { PHASE_SWEEP_MARK_INCOMING_GRAY, "Mark Incoming Gray Pointers", PHASE_SWEEP_MARK },
     { PHASE_SWEEP_MARK_GRAY, "Mark Gray", PHASE_SWEEP_MARK },
     { PHASE_SWEEP_MARK_GRAY_WEAK, "Mark Gray and Weak", PHASE_SWEEP_MARK },
     { PHASE_FINALIZE_START, "Finalize Start Callback", PHASE_SWEEP },
     { PHASE_SWEEP_ATOMS, "Sweep Atoms", PHASE_SWEEP },
     { PHASE_SWEEP_COMPARTMENTS, "Sweep Compartments", PHASE_SWEEP },
     { PHASE_SWEEP_DISCARD_CODE, "Sweep Discard Code", PHASE_SWEEP_COMPARTMENTS },
     { PHASE_SWEEP_TABLES, "Sweep Tables", PHASE_SWEEP_COMPARTMENTS },
     { PHASE_SWEEP_TABLES_WRAPPER, "Sweep Cross Compartment Wrappers", PHASE_SWEEP_TABLES },
     { PHASE_SWEEP_TABLES_BASE_SHAPE, "Sweep Base Shapes", PHASE_SWEEP_TABLES },
     { PHASE_SWEEP_TABLES_INITIAL_SHAPE, "Sweep Initial Shapes", PHASE_SWEEP_TABLES },
     { PHASE_SWEEP_TABLES_TYPE_OBJECT, "Sweep Type Objects", PHASE_SWEEP_TABLES },
     { PHASE_SWEEP_TABLES_BREAKPOINT, "Sweep Breakpoints", PHASE_SWEEP_TABLES },
     { PHASE_SWEEP_TABLES_REGEXP, "Sweep Regexps", PHASE_SWEEP_TABLES },
     { PHASE_DISCARD_ANALYSIS, "Discard Analysis", PHASE_SWEEP_COMPARTMENTS },
     { PHASE_DISCARD_TI, "Discard TI", PHASE_DISCARD_ANALYSIS },
     { PHASE_FREE_TI_ARENA, "Free TI Arena", PHASE_DISCARD_ANALYSIS },
     { PHASE_SWEEP_TYPES, "Sweep Types", PHASE_DISCARD_ANALYSIS },
     { PHASE_SWEEP_OBJECT, "Sweep Object", PHASE_SWEEP },
     { PHASE_SWEEP_STRING, "Sweep String", PHASE_SWEEP },
     { PHASE_SWEEP_SCRIPT, "Sweep Script", PHASE_SWEEP },
     { PHASE_SWEEP_SHAPE, "Sweep Shape", PHASE_SWEEP },
     { PHASE_SWEEP_JITCODE, "Sweep JIT code", PHASE_SWEEP },
     { PHASE_FINALIZE_END, "Finalize End Callback", PHASE_SWEEP },
     { PHASE_DESTROY, "Deallocate", PHASE_SWEEP },
     { PHASE_GC_END, "End Callback", PHASE_NO_PARENT },
     { PHASE_LIMIT, nullptr, PHASE_NO_PARENT }
 };
 static void
 FormatPhaseTimes(StatisticsSerializer &ss, const char *name, int64_t *times)
 {
     ss.beginObject(name);
     for (unsigned i = 0; phases[i].name; i++)
         ss.appendIfNonzeroMS(phases[i].name, t(times[phases[i].index]));
     ss.endObject();
 }
 void
 Statistics::gcDuration(int64_t *total, int64_t *maxPause)
 {
     *total = *maxPause = 0;
     for (SliceData *slice = slices.begin(); slice != slices.end(); slice++) {
         *total += slice->duration();
         if (slice->duration() > *maxPause)
             *maxPause = slice->duration();
     }
 }
 void
 Statistics::sccDurations(int64_t *total, int64_t *maxPause)
 {
     *total = *maxPause = 0;
     for (size_t i = 0; i < sccTimes.length(); i++) {
         *total += sccTimes[i];
         *maxPause = Max(*maxPause, sccTimes[i]);
     }
 }
 bool
 Statistics::formatData(StatisticsSerializer &ss, uint64_t timestamp)
 {
     int64_t total, longest;
     gcDuration(&total, &longest);
     int64_t sccTotal, sccLongest;
     sccDurations(&sccTotal, &sccLongest);
     double mmu20 = computeMMU(20 * PRMJ_USEC_PER_MSEC);
     double mmu50 = computeMMU(50 * PRMJ_USEC_PER_MSEC);
     ss.beginObject(nullptr);
     if (ss.isJSON())
         ss.appendNumber("Timestamp", "%llu", "", (unsigned long long)timestamp);
     if (slices.length() > 1 || ss.isJSON())
         ss.appendDecimal("Max Pause", "ms", t(longest));
     else
         ss.appendString("Reason", ExplainReason(slices[0].reason));
     ss.appendDecimal("Total Time", "ms", t(total));
     ss.appendNumber("Zones Collected", "%d", "", collectedCount);
     ss.appendNumber("Total Zones", "%d", "", zoneCount);
     ss.appendNumber("Total Compartments", "%d", "", compartmentCount);
     ss.appendNumber("Minor GCs", "%d", "", counts[STAT_MINOR_GC]);
     ss.appendNumber("MMU (20ms)", "%d", "%", int(mmu20 * 100));
     ss.appendNumber("MMU (50ms)", "%d", "%", int(mmu50 * 100));
     ss.appendDecimal("SCC Sweep Total", "ms", t(sccTotal));
     ss.appendDecimal("SCC Sweep Max Pause", "ms", t(sccLongest));
     if (nonincrementalReason || ss.isJSON()) {
         ss.appendString("Nonincremental Reason",
                         nonincrementalReason ? nonincrementalReason : "none");
     }
     ss.appendNumber("Allocated", "%u", "MB", unsigned(preBytes / 1024 / 1024));
     ss.appendNumber("+Chunks", "%d", "", counts[STAT_NEW_CHUNK]);
     ss.appendNumber("-Chunks", "%d", "", counts[STAT_DESTROY_CHUNK]);
     ss.endLine();
     if (slices.length() > 1 || ss.isJSON()) {
         ss.beginArray("Slices");
         for (size_t i = 0; i < slices.length(); i++) {
             int64_t width = slices[i].duration();
             if (i != 0 && i != slices.length() - 1 && width < SLICE_MIN_REPORT_TIME &&
                 !slices[i].resetReason && !ss.isJSON())
             {
                 continue;
             }
             ss.beginObject(nullptr);
             ss.extra("    ");
             ss.appendNumber("Slice", "%d", "", i);
             ss.appendDecimal("Pause", "", t(width));
             ss.extra(" (");
             ss.appendDecimal("When", "ms", t(slices[i].start - slices[0].start));
             ss.appendString("Reason", ExplainReason(slices[i].reason));
             if (ss.isJSON()) {
                 ss.appendDecimal("Page Faults", "",
                                  double(slices[i].endFaults - slices[i].startFaults));
                 ss.appendNumber("Start Timestamp", "%llu", "", (unsigned long long)slices[i].start);
                 ss.appendNumber("End Timestamp", "%llu", "", (unsigned long long)slices[i].end);
             }
             if (slices[i].resetReason)
                 ss.appendString("Reset", slices[i].resetReason);
             ss.extra("): ");
             FormatPhaseTimes(ss, "Times", slices[i].phaseTimes);
             ss.endLine();
             ss.endObject();
         }
         ss.endArray();
     }
     ss.extra("    Totals: ");
     FormatPhaseTimes(ss, "Totals", phaseTimes);
     ss.endObject();
     return !ss.isOOM();
 }
 jschar *
 Statistics::formatMessage()
 {
     StatisticsSerializer ss(StatisticsSerializer::AsText);
     formatData(ss, 0);
     return ss.finishJSString();
 }
 jschar *
 Statistics::formatJSON(uint64_t timestamp)
 {
     StatisticsSerializer ss(StatisticsSerializer::AsJSON);
     formatData(ss, timestamp);
     return ss.finishJSString();
 }
 Statistics::Statistics(JSRuntime *rt)
   : runtime(rt),
     startupTime(PRMJ_Now()),
     fp(nullptr),
     fullFormat(false),
     gcDepth(0),
     collectedCount(0),
     zoneCount(0),
     compartmentCount(0),
     nonincrementalReason(nullptr),
     preBytes(0),
     phaseNestingDepth(0)
 {
     PodArrayZero(phaseTotals);
     PodArrayZero(counts);
     char *env = getenv("MOZ_GCTIMER");
     if (!env || strcmp(env, "none") == 0) {
         fp = nullptr;
         return;
     }
     if (strcmp(env, "stdout") == 0) {
         fullFormat = false;
         fp = stdout;
     } else if (strcmp(env, "stderr") == 0) {
         fullFormat = false;
         fp = stderr;
     } else {
         fullFormat = true;
         fp = fopen(env, "a");
         JS_ASSERT(fp);
     }
 }
 Statistics::~Statistics()
 {
     if (fp) {
         if (fullFormat) {
             StatisticsSerializer ss(StatisticsSerializer::AsText);
             FormatPhaseTimes(ss, "", phaseTotals);
             char *msg = ss.finishCString();
             if (msg) {
                 fprintf(fp, "TOTALS\n%s\n\n-------\n", msg);
                 js_free(msg);
             }
         }
         if (fp != stdout && fp != stderr)
             fclose(fp);
     }
 }
 void
 Statistics::printStats()
 {
     if (fullFormat) {
         StatisticsSerializer ss(StatisticsSerializer::AsText);
         formatData(ss, 0);
         char *msg = ss.finishCString();
         if (msg) {
             fprintf(fp, "GC(T+%.3fs) %s\n", t(slices[0].start - startupTime) / 1000.0, msg);
             js_free(msg);
         }
     } else {
         int64_t total, longest;
         gcDuration(&total, &longest);
         fprintf(fp, "%f %f %f\n",
                 t(total),
                 t(phaseTimes[PHASE_MARK]),
                 t(phaseTimes[PHASE_SWEEP]));
     }
     fflush(fp);
 }
 void
 Statistics::beginGC()
 {
     PodArrayZero(phaseStartTimes);
     PodArrayZero(phaseTimes);
     slices.clearAndFree();
     sccTimes.clearAndFree();
     nonincrementalReason = nullptr;
     preBytes = runtime->gcBytes;
 }
 void
 Statistics::endGC()
 {
     crash::SnapshotGCStack();
     for (int i = 0; i < PHASE_LIMIT; i++)
         phaseTotals[i] += phaseTimes[i];
     if (JSAccumulateTelemetryDataCallback cb = runtime->telemetryCallback) {
         int64_t total, longest;
         gcDuration(&total, &longest);
         int64_t sccTotal, sccLongest;
         sccDurations(&sccTotal, &sccLongest);
         (*cb)(JS_TELEMETRY_GC_IS_COMPARTMENTAL, collectedCount == zoneCount ? 0 : 1);
         (*cb)(JS_TELEMETRY_GC_MS, t(total));
         (*cb)(JS_TELEMETRY_GC_MAX_PAUSE_MS, t(longest));
         (*cb)(JS_TELEMETRY_GC_MARK_MS, t(phaseTimes[PHASE_MARK]));
         (*cb)(JS_TELEMETRY_GC_SWEEP_MS, t(phaseTimes[PHASE_SWEEP]));
         (*cb)(JS_TELEMETRY_GC_MARK_ROOTS_MS, t(phaseTimes[PHASE_MARK_ROOTS]));
         (*cb)(JS_TELEMETRY_GC_MARK_GRAY_MS, t(phaseTimes[PHASE_SWEEP_MARK_GRAY]));
         (*cb)(JS_TELEMETRY_GC_NON_INCREMENTAL, !!nonincrementalReason);
         (*cb)(JS_TELEMETRY_GC_INCREMENTAL_DISABLED, !runtime->gcIncrementalEnabled);
         (*cb)(JS_TELEMETRY_GC_SCC_SWEEP_TOTAL_MS, t(sccTotal));
         (*cb)(JS_TELEMETRY_GC_SCC_SWEEP_MAX_PAUSE_MS, t(sccLongest));
         double mmu50 = computeMMU(50 * PRMJ_USEC_PER_MSEC);
         (*cb)(JS_TELEMETRY_GC_MMU_50, mmu50 * 100);
     }
     if (fp)
         printStats();
 }
 void
 Statistics::beginSlice(int collectedCount, int zoneCount, int compartmentCount,
                        JS::gcreason::Reason reason)
 {
     this->collectedCount = collectedCount;
     this->zoneCount = zoneCount;
     this->compartmentCount = compartmentCount;
     bool first = runtime->gcIncrementalState == gc::NO_INCREMENTAL;
     if (first)
         beginGC();
     SliceData data(reason, PRMJ_Now(), gc::GetPageFaultCount());
     (void) slices.append(data); /* Ignore any OOMs here. */
     if (JSAccumulateTelemetryDataCallback cb = runtime->telemetryCallback)
         (*cb)(JS_TELEMETRY_GC_REASON, reason);
     // Slice callbacks should only fire for the outermost level
     if (++gcDepth == 1) {
         bool wasFullGC = collectedCount == zoneCount;
         if (JS::GCSliceCallback cb = runtime->gcSliceCallback)
             (*cb)(runtime, first ? JS::GC_CYCLE_BEGIN : JS::GC_SLICE_BEGIN,
                   JS::GCDescription(!wasFullGC));
     }
 }
 void
 Statistics::endSlice()
 {
     slices.back().end = PRMJ_Now();
     slices.back().endFaults = gc::GetPageFaultCount();
     if (JSAccumulateTelemetryDataCallback cb = runtime->telemetryCallback) {
         (*cb)(JS_TELEMETRY_GC_SLICE_MS, t(slices.back().end - slices.back().start));
         (*cb)(JS_TELEMETRY_GC_RESET, !!slices.back().resetReason);
     }
     bool last = runtime->gcIncrementalState == gc::NO_INCREMENTAL;
     if (last)
         endGC();
     // Slice callbacks should only fire for the outermost level
     if (--gcDepth == 0) {
         bool wasFullGC = collectedCount == zoneCount;
         if (JS::GCSliceCallback cb = runtime->gcSliceCallback)
             (*cb)(runtime, last ? JS::GC_CYCLE_END : JS::GC_SLICE_END,
                   JS::GCDescription(!wasFullGC));
     }
     /* Do this after the slice callback since it uses these values. */
     if (last)
         PodArrayZero(counts);
 }
 void
 Statistics::beginPhase(Phase phase)
 {
     /* Guard against re-entry */
     JS_ASSERT(!phaseStartTimes[phase]);
 #ifdef DEBUG
     JS_ASSERT(phases[phase].index == phase);
     Phase parent = phaseNestingDepth ? phaseNesting[phaseNestingDepth - 1] : PHASE_NO_PARENT;
     JS_ASSERT(phaseNestingDepth < MAX_NESTING);
     JS_ASSERT_IF(gcDepth == 1, phases[phase].parent == parent);
     phaseNesting[phaseNestingDepth] = phase;
     phaseNestingDepth++;
 #endif
     phaseStartTimes[phase] = PRMJ_Now();
 }
 void
 Statistics::endPhase(Phase phase)
 {
     phaseNestingDepth--;
     int64_t t = PRMJ_Now() - phaseStartTimes[phase];
     slices.back().phaseTimes[phase] += t;
     phaseTimes[phase] += t;
     phaseStartTimes[phase] = 0;
 }
 int64_t
 Statistics::beginSCC()
 {
     return PRMJ_Now();
 }
 void
 Statistics::endSCC(unsigned scc, int64_t start)
 {
     if (scc >= sccTimes.length() && !sccTimes.resize(scc + 1))
         return;
     sccTimes[scc] += PRMJ_Now() - start;
 }
 /*
  * MMU (minimum mutator utilization) is a measure of how much garbage collection
  * is affecting the responsiveness of the system. MMU measurements are given
  * with respect to a certain window size. If we report MMU(50ms) = 80%, then
  * that means that, for any 50ms window of time, at least 80% of the window is
  * devoted to the mutator. In other words, the GC is running for at most 20% of
  * the window, or 10ms. The GC can run multiple slices during the 50ms window
  * as long as the total time it spends is at most 10ms.
  */
 double
 Statistics::computeMMU(int64_t window)
 {
     JS_ASSERT(!slices.empty());
     int64_t gc = slices[0].end - slices[0].start;
     int64_t gcMax = gc;
     if (gc >= window)
         return 0.0;
     int startIndex = 0;
     for (size_t endIndex = 1; endIndex < slices.length(); endIndex++) {
         gc += slices[endIndex].end - slices[endIndex].start;
         while (slices[endIndex].end - slices[startIndex].end >= window) {
             gc -= slices[startIndex].end - slices[startIndex].start;
             startIndex++;
         }
         int64_t cur = gc;
         if (slices[endIndex].end - slices[startIndex].start > window)
             cur -= (slices[endIndex].end - slices[startIndex].start - window);
         if (cur > gcMax)
             gcMax = cur;
     }
     return double(window - gcMax) / window;
 }

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js/src/gc/Statistics.cpp@b8a032363ba2 (annotated)

js/src/gc/Statistics.cpp