Add m-esr52 at 52.6.0

1 files changed, 1025 insertions, 0 deletions

diff --git a/js/src/gc/Nursery.cpp b/js/src/gc/Nursery.cpp
new file mode 100644
index 000000000..2c402fe0b
--- /dev/null
+++ b/js/src/gc/Nursery.cpp
@@ -0,0 +1,1025 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sw=4 et tw=78:
+ *
+ * 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/Nursery-inl.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/Move.h"
+#include "mozilla/Unused.h"
+
+#include "jscompartment.h"
+#include "jsfriendapi.h"
+#include "jsgc.h"
+#include "jsutil.h"
+
+#include "gc/GCInternals.h"
+#include "gc/Memory.h"
+#include "jit/JitFrames.h"
+#include "vm/ArrayObject.h"
+#include "vm/Debugger.h"
+#if defined(DEBUG)
+#include "vm/EnvironmentObject.h"
+#endif
+#include "vm/Time.h"
+#include "vm/TypedArrayObject.h"
+#include "vm/TypeInference.h"
+
+#include "jsobjinlines.h"
+
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+using namespace gc;
+
+using mozilla::ArrayLength;
+using mozilla::DebugOnly;
+using mozilla::PodCopy;
+using mozilla::PodZero;
+
+static const uintptr_t CanaryMagicValue = 0xDEADB15D;
+
+struct js::Nursery::FreeMallocedBuffersTask : public GCParallelTask
+{
+    explicit FreeMallocedBuffersTask(FreeOp* fop) : fop_(fop) {}
+    bool init() { return buffers_.init(); }
+    void transferBuffersToFree(MallocedBuffersSet& buffersToFree,
+                               const AutoLockHelperThreadState& lock);
+    ~FreeMallocedBuffersTask() override { join(); }
+
+  private:
+    FreeOp* fop_;
+    MallocedBuffersSet buffers_;
+
+    virtual void run() override;
+};
+
+struct js::Nursery::SweepAction
+{
+    SweepAction(SweepThunk thunk, void* data, SweepAction* next)
+      : thunk(thunk), data(data), next(next)
+    {}
+
+    SweepThunk thunk;
+    void* data;
+    SweepAction* next;
+
+#if JS_BITS_PER_WORD == 32
+  protected:
+    uint32_t padding;
+#endif
+};
+
+#ifdef JS_GC_ZEAL
+struct js::Nursery::Canary
+{
+    uintptr_t magicValue;
+    Canary* next;
+};
+#endif
+
+inline void
+js::Nursery::NurseryChunk::poisonAndInit(JSRuntime* rt, uint8_t poison)
+{
+    JS_POISON(this, poison, ChunkSize);
+    init(rt);
+}
+
+inline void
+js::Nursery::NurseryChunk::init(JSRuntime* rt)
+{
+    new (&trailer) gc::ChunkTrailer(rt, &rt->gc.storeBuffer);
+}
+
+/* static */ inline js::Nursery::NurseryChunk*
+js::Nursery::NurseryChunk::fromChunk(Chunk* chunk)
+{
+    return reinterpret_cast<NurseryChunk*>(chunk);
+}
+
+inline Chunk*
+js::Nursery::NurseryChunk::toChunk(JSRuntime* rt)
+{
+    auto chunk = reinterpret_cast<Chunk*>(this);
+    chunk->init(rt);
+    return chunk;
+}
+
+js::Nursery::Nursery(JSRuntime* rt)
+  : runtime_(rt)
+  , position_(0)
+  , currentStartChunk_(0)
+  , currentStartPosition_(0)
+  , currentEnd_(0)
+  , currentChunk_(0)
+  , maxNurseryChunks_(0)
+  , previousPromotionRate_(0)
+  , profileThreshold_(0)
+  , enableProfiling_(false)
+  , reportTenurings_(0)
+  , minorGcCount_(0)
+  , freeMallocedBuffersTask(nullptr)
+  , sweepActions_(nullptr)
+#ifdef JS_GC_ZEAL
+  , lastCanary_(nullptr)
+#endif
+{}
+
+bool
+js::Nursery::init(uint32_t maxNurseryBytes, AutoLockGC& lock)
+{
+    /* maxNurseryBytes parameter is rounded down to a multiple of chunk size. */
+    maxNurseryChunks_ = maxNurseryBytes >> ChunkShift;
+
+    /* If no chunks are specified then the nursery is permenantly disabled. */
+    if (maxNurseryChunks_ == 0)
+        return true;
+
+    if (!mallocedBuffers.init())
+        return false;
+
+    if (!cellsWithUid_.init())
+        return false;
+
+    freeMallocedBuffersTask = js_new<FreeMallocedBuffersTask>(runtime()->defaultFreeOp());
+    if (!freeMallocedBuffersTask || !freeMallocedBuffersTask->init())
+        return false;
+
+    AutoMaybeStartBackgroundAllocation maybeBgAlloc;
+    updateNumChunksLocked(1, maybeBgAlloc, lock);
+    if (numChunks() == 0)
+        return false;
+
+    setCurrentChunk(0);
+    setStartPosition();
+
+    char* env = getenv("JS_GC_PROFILE_NURSERY");
+    if (env) {
+        if (0 == strcmp(env, "help")) {
+            fprintf(stderr, "JS_GC_PROFILE_NURSERY=N\n"
+                    "\tReport minor GC's taking at least N microseconds.\n");
+            exit(0);
+        }
+        enableProfiling_ = true;
+        profileThreshold_ = atoi(env);
+    }
+
+    env = getenv("JS_GC_REPORT_TENURING");
+    if (env) {
+        if (0 == strcmp(env, "help")) {
+            fprintf(stderr, "JS_GC_REPORT_TENURING=N\n"
+                    "\tAfter a minor GC, report any ObjectGroups with at least N instances tenured.\n");
+            exit(0);
+        }
+        reportTenurings_ = atoi(env);
+    }
+
+    PodZero(&startTimes_);
+    PodZero(&profileTimes_);
+    PodZero(&totalTimes_);
+
+    if (!runtime()->gc.storeBuffer.enable())
+        return false;
+
+    MOZ_ASSERT(isEnabled());
+    return true;
+}
+
+js::Nursery::~Nursery()
+{
+    disable();
+    js_delete(freeMallocedBuffersTask);
+}
+
+void
+js::Nursery::enable()
+{
+    MOZ_ASSERT(isEmpty());
+    MOZ_ASSERT(!runtime()->gc.isVerifyPreBarriersEnabled());
+    if (isEnabled())
+        return;
+
+    updateNumChunks(1);
+    if (numChunks() == 0)
+        return;
+
+    setCurrentChunk(0);
+    setStartPosition();
+#ifdef JS_GC_ZEAL
+    if (runtime()->hasZealMode(ZealMode::GenerationalGC))
+        enterZealMode();
+#endif
+
+    MOZ_ALWAYS_TRUE(runtime()->gc.storeBuffer.enable());
+    return;
+}
+
+void
+js::Nursery::disable()
+{
+    MOZ_ASSERT(isEmpty());
+    if (!isEnabled())
+        return;
+    updateNumChunks(0);
+    currentEnd_ = 0;
+    runtime()->gc.storeBuffer.disable();
+}
+
+bool
+js::Nursery::isEmpty() const
+{
+    MOZ_ASSERT(runtime_);
+    if (!isEnabled())
+        return true;
+
+    if (!runtime_->hasZealMode(ZealMode::GenerationalGC)) {
+        MOZ_ASSERT(currentStartChunk_ == 0);
+        MOZ_ASSERT(currentStartPosition_ == chunk(0).start());
+    }
+    return position() == currentStartPosition_;
+}
+
+#ifdef JS_GC_ZEAL
+void
+js::Nursery::enterZealMode() {
+    if (isEnabled())
+        updateNumChunks(maxNurseryChunks_);
+}
+
+void
+js::Nursery::leaveZealMode() {
+    if (isEnabled()) {
+        MOZ_ASSERT(isEmpty());
+        setCurrentChunk(0);
+        setStartPosition();
+    }
+}
+#endif // JS_GC_ZEAL
+
+JSObject*
+js::Nursery::allocateObject(JSContext* cx, size_t size, size_t numDynamic, const js::Class* clasp)
+{
+    /* Ensure there's enough space to replace the contents with a RelocationOverlay. */
+    MOZ_ASSERT(size >= sizeof(RelocationOverlay));
+
+    /* Sanity check the finalizer. */
+    MOZ_ASSERT_IF(clasp->hasFinalize(), CanNurseryAllocateFinalizedClass(clasp) ||
+                                        clasp->isProxy());
+
+    /* Make the object allocation. */
+    JSObject* obj = static_cast<JSObject*>(allocate(size));
+    if (!obj)
+        return nullptr;
+
+    /* If we want external slots, add them. */
+    HeapSlot* slots = nullptr;
+    if (numDynamic) {
+        MOZ_ASSERT(clasp->isNative() || clasp->isProxy());
+        slots = static_cast<HeapSlot*>(allocateBuffer(cx->zone(), numDynamic * sizeof(HeapSlot)));
+        if (!slots) {
+            /*
+             * It is safe to leave the allocated object uninitialized, since we
+             * do not visit unallocated things in the nursery.
+             */
+            return nullptr;
+        }
+    }
+
+    /* Always initialize the slots field to match the JIT behavior. */
+    obj->setInitialSlotsMaybeNonNative(slots);
+
+    TraceNurseryAlloc(obj, size);
+    return obj;
+}
+
+void*
+js::Nursery::allocate(size_t size)
+{
+    MOZ_ASSERT(isEnabled());
+    MOZ_ASSERT(!runtime()->isHeapBusy());
+    MOZ_ASSERT_IF(currentChunk_ == currentStartChunk_, position() >= currentStartPosition_);
+    MOZ_ASSERT(position() % gc::CellSize == 0);
+    MOZ_ASSERT(size % gc::CellSize == 0);
+
+#ifdef JS_GC_ZEAL
+    static const size_t CanarySize = (sizeof(Nursery::Canary) + CellSize - 1) & ~CellMask;
+    if (runtime()->gc.hasZealMode(ZealMode::CheckNursery))
+        size += CanarySize;
+#endif
+
+    if (currentEnd() < position() + size) {
+        if (currentChunk_ + 1 == numChunks())
+            return nullptr;
+        setCurrentChunk(currentChunk_ + 1);
+    }
+
+    void* thing = (void*)position();
+    position_ = position() + size;
+
+    JS_EXTRA_POISON(thing, JS_ALLOCATED_NURSERY_PATTERN, size);
+
+#ifdef JS_GC_ZEAL
+    if (runtime()->gc.hasZealMode(ZealMode::CheckNursery)) {
+        auto canary = reinterpret_cast<Canary*>(position() - CanarySize);
+        canary->magicValue = CanaryMagicValue;
+        canary->next = nullptr;
+        if (lastCanary_) {
+            MOZ_ASSERT(!lastCanary_->next);
+            lastCanary_->next = canary;
+        }
+        lastCanary_ = canary;
+    }
+#endif
+
+    MemProfiler::SampleNursery(reinterpret_cast<void*>(thing), size);
+    return thing;
+}
+
+void*
+js::Nursery::allocateBuffer(Zone* zone, size_t nbytes)
+{
+    MOZ_ASSERT(nbytes > 0);
+
+    if (nbytes <= MaxNurseryBufferSize) {
+        void* buffer = allocate(nbytes);
+        if (buffer)
+            return buffer;
+    }
+
+    void* buffer = zone->pod_malloc<uint8_t>(nbytes);
+    if (buffer && !mallocedBuffers.putNew(buffer)) {
+        js_free(buffer);
+        return nullptr;
+    }
+    return buffer;
+}
+
+void*
+js::Nursery::allocateBuffer(JSObject* obj, size_t nbytes)
+{
+    MOZ_ASSERT(obj);
+    MOZ_ASSERT(nbytes > 0);
+
+    if (!IsInsideNursery(obj))
+        return obj->zone()->pod_malloc<uint8_t>(nbytes);
+    return allocateBuffer(obj->zone(), nbytes);
+}
+
+void*
+js::Nursery::reallocateBuffer(JSObject* obj, void* oldBuffer,
+                              size_t oldBytes, size_t newBytes)
+{
+    if (!IsInsideNursery(obj))
+        return obj->zone()->pod_realloc<uint8_t>((uint8_t*)oldBuffer, oldBytes, newBytes);
+
+    if (!isInside(oldBuffer)) {
+        void* newBuffer = obj->zone()->pod_realloc<uint8_t>((uint8_t*)oldBuffer, oldBytes, newBytes);
+        if (newBuffer && oldBuffer != newBuffer)
+            MOZ_ALWAYS_TRUE(mallocedBuffers.rekeyAs(oldBuffer, newBuffer, newBuffer));
+        return newBuffer;
+    }
+
+    /* The nursery cannot make use of the returned slots data. */
+    if (newBytes < oldBytes)
+        return oldBuffer;
+
+    void* newBuffer = allocateBuffer(obj->zone(), newBytes);
+    if (newBuffer)
+        PodCopy((uint8_t*)newBuffer, (uint8_t*)oldBuffer, oldBytes);
+    return newBuffer;
+}
+
+void
+js::Nursery::freeBuffer(void* buffer)
+{
+    if (!isInside(buffer)) {
+        removeMallocedBuffer(buffer);
+        js_free(buffer);
+    }
+}
+
+void
+Nursery::setForwardingPointer(void* oldData, void* newData, bool direct)
+{
+    MOZ_ASSERT(isInside(oldData));
+
+    // Bug 1196210: If a zero-capacity header lands in the last 2 words of a
+    // jemalloc chunk abutting the start of a nursery chunk, the (invalid)
+    // newData pointer will appear to be "inside" the nursery.
+    MOZ_ASSERT(!isInside(newData) || (uintptr_t(newData) & ChunkMask) == 0);
+
+    if (direct) {
+        *reinterpret_cast<void**>(oldData) = newData;
+    } else {
+        AutoEnterOOMUnsafeRegion oomUnsafe;
+        if (!forwardedBuffers.initialized() && !forwardedBuffers.init())
+            oomUnsafe.crash("Nursery::setForwardingPointer");
+#ifdef DEBUG
+        if (ForwardedBufferMap::Ptr p = forwardedBuffers.lookup(oldData))
+            MOZ_ASSERT(p->value() == newData);
+#endif
+        if (!forwardedBuffers.put(oldData, newData))
+            oomUnsafe.crash("Nursery::setForwardingPointer");
+    }
+}
+
+void
+Nursery::setSlotsForwardingPointer(HeapSlot* oldSlots, HeapSlot* newSlots, uint32_t nslots)
+{
+    // Slot arrays always have enough space for a forwarding pointer, since the
+    // number of slots is never zero.
+    MOZ_ASSERT(nslots > 0);
+    setForwardingPointer(oldSlots, newSlots, /* direct = */ true);
+}
+
+void
+Nursery::setElementsForwardingPointer(ObjectElements* oldHeader, ObjectElements* newHeader,
+                                      uint32_t nelems)
+{
+    // Only use a direct forwarding pointer if there is enough space for one.
+    setForwardingPointer(oldHeader->elements(), newHeader->elements(),
+                         nelems > ObjectElements::VALUES_PER_HEADER);
+}
+
+#ifdef DEBUG
+static bool IsWriteableAddress(void* ptr)
+{
+    volatile uint64_t* vPtr = reinterpret_cast<volatile uint64_t*>(ptr);
+    *vPtr = *vPtr;
+    return true;
+}
+#endif
+
+void
+js::Nursery::forwardBufferPointer(HeapSlot** pSlotsElems)
+{
+    HeapSlot* old = *pSlotsElems;
+
+    if (!isInside(old))
+        return;
+
+    // The new location for this buffer is either stored inline with it or in
+    // the forwardedBuffers table.
+    do {
+        if (forwardedBuffers.initialized()) {
+            if (ForwardedBufferMap::Ptr p = forwardedBuffers.lookup(old)) {
+                *pSlotsElems = reinterpret_cast<HeapSlot*>(p->value());
+                break;
+            }
+        }
+
+        *pSlotsElems = *reinterpret_cast<HeapSlot**>(old);
+    } while (false);
+
+    MOZ_ASSERT(!isInside(*pSlotsElems));
+    MOZ_ASSERT(IsWriteableAddress(*pSlotsElems));
+}
+
+js::TenuringTracer::TenuringTracer(JSRuntime* rt, Nursery* nursery)
+  : JSTracer(rt, JSTracer::TracerKindTag::Tenuring, TraceWeakMapKeysValues)
+  , nursery_(*nursery)
+  , tenuredSize(0)
+  , head(nullptr)
+  , tail(&head)
+{
+}
+
+/* static */ void
+js::Nursery::printProfileHeader()
+{
+#define PRINT_HEADER(name, text)                                              \
+    fprintf(stderr, " %6s", text);
+FOR_EACH_NURSERY_PROFILE_TIME(PRINT_HEADER)
+#undef PRINT_HEADER
+    fprintf(stderr, "\n");
+}
+
+/* static */ void
+js::Nursery::printProfileTimes(const ProfileTimes& times)
+{
+    for (auto time : times)
+        fprintf(stderr, " %6" PRIi64, time);
+    fprintf(stderr, "\n");
+}
+
+void
+js::Nursery::printTotalProfileTimes()
+{
+    if (enableProfiling_) {
+        fprintf(stderr, "MinorGC TOTALS: %7" PRIu64 " collections:      ", minorGcCount_);
+        printProfileTimes(totalTimes_);
+    }
+}
+
+inline void
+js::Nursery::startProfile(ProfileKey key)
+{
+    startTimes_[key] = PRMJ_Now();
+}
+
+inline void
+js::Nursery::endProfile(ProfileKey key)
+{
+    profileTimes_[key] = PRMJ_Now() - startTimes_[key];
+    totalTimes_[key] += profileTimes_[key];
+}
+
+inline void
+js::Nursery::maybeStartProfile(ProfileKey key)
+{
+    if (enableProfiling_)
+        startProfile(key);
+}
+
+inline void
+js::Nursery::maybeEndProfile(ProfileKey key)
+{
+    if (enableProfiling_)
+        endProfile(key);
+}
+
+void
+js::Nursery::collect(JSRuntime* rt, JS::gcreason::Reason reason)
+{
+    MOZ_ASSERT(!rt->mainThread.suppressGC);
+    MOZ_RELEASE_ASSERT(CurrentThreadCanAccessRuntime(rt));
+
+    if (!isEnabled() || isEmpty()) {
+        // Our barriers are not always exact, and there may be entries in the
+        // storebuffer even when the nursery is disabled or empty. It's not safe
+        // to keep these entries as they may refer to tenured cells which may be
+        // freed after this point.
+        rt->gc.storeBuffer.clear();
+    }
+
+    if (!isEnabled())
+        return;
+
+    rt->gc.incMinorGcNumber();
+
+#ifdef JS_GC_ZEAL
+    if (rt->gc.hasZealMode(ZealMode::CheckNursery)) {
+        for (auto canary = lastCanary_; canary; canary = canary->next)
+            MOZ_ASSERT(canary->magicValue == CanaryMagicValue);
+    }
+    lastCanary_ = nullptr;
+#endif
+
+    rt->gc.stats.beginNurseryCollection(reason);
+    TraceMinorGCStart();
+
+    startProfile(ProfileKey::Total);
+
+    // The hazard analysis thinks doCollection can invalidate pointers in
+    // tenureCounts below.
+    JS::AutoSuppressGCAnalysis nogc;
+
+    TenureCountCache tenureCounts;
+    double promotionRate = 0;
+    if (!isEmpty())
+        promotionRate = doCollection(rt, reason, tenureCounts);
+
+    // Resize the nursery.
+    maybeStartProfile(ProfileKey::Resize);
+    maybeResizeNursery(reason, promotionRate);
+    maybeEndProfile(ProfileKey::Resize);
+
+    // If we are promoting the nursery, or exhausted the store buffer with
+    // pointers to nursery things, which will force a collection well before
+    // the nursery is full, look for object groups that are getting promoted
+    // excessively and try to pretenure them.
+    maybeStartProfile(ProfileKey::Pretenure);
+    uint32_t pretenureCount = 0;
+    if (promotionRate > 0.8 || reason == JS::gcreason::FULL_STORE_BUFFER) {
+        JSContext* cx = rt->contextFromMainThread();
+        for (auto& entry : tenureCounts.entries) {
+            if (entry.count >= 3000) {
+                ObjectGroup* group = entry.group;
+                if (group->canPreTenure()) {
+                    AutoCompartment ac(cx, group->compartment());
+                    group->setShouldPreTenure(cx);
+                    pretenureCount++;
+                }
+            }
+        }
+    }
+    maybeEndProfile(ProfileKey::Pretenure);
+
+    // We ignore gcMaxBytes when allocating for minor collection. However, if we
+    // overflowed, we disable the nursery. The next time we allocate, we'll fail
+    // because gcBytes >= gcMaxBytes.
+    if (rt->gc.usage.gcBytes() >= rt->gc.tunables.gcMaxBytes())
+        disable();
+
+    endProfile(ProfileKey::Total);
+    minorGcCount_++;
+
+    int64_t totalTime = profileTimes_[ProfileKey::Total];
+    rt->addTelemetry(JS_TELEMETRY_GC_MINOR_US, totalTime);
+    rt->addTelemetry(JS_TELEMETRY_GC_MINOR_REASON, reason);
+    if (totalTime > 1000)
+        rt->addTelemetry(JS_TELEMETRY_GC_MINOR_REASON_LONG, reason);
+    rt->addTelemetry(JS_TELEMETRY_GC_NURSERY_BYTES, sizeOfHeapCommitted());
+    rt->addTelemetry(JS_TELEMETRY_GC_PRETENURE_COUNT, pretenureCount);
+
+    rt->gc.stats.endNurseryCollection(reason);
+    TraceMinorGCEnd();
+
+    if (enableProfiling_ && totalTime >= profileThreshold_) {
+        static int printedHeader = 0;
+        if ((printedHeader++ % 200) == 0) {
+            fprintf(stderr, "MinorGC:               Reason  PRate Size ");
+            printProfileHeader();
+        }
+
+        fprintf(stderr, "MinorGC: %20s %5.1f%% %4u ",
+                JS::gcreason::ExplainReason(reason),
+                promotionRate * 100,
+                numChunks());
+        printProfileTimes(profileTimes_);
+
+        if (reportTenurings_) {
+            for (auto& entry : tenureCounts.entries) {
+                if (entry.count >= reportTenurings_) {
+                    fprintf(stderr, "%d x ", entry.count);
+                    entry.group->print();
+                }
+            }
+        }
+    }
+}
+
+double
+js::Nursery::doCollection(JSRuntime* rt, JS::gcreason::Reason reason,
+                          TenureCountCache& tenureCounts)
+{
+    AutoTraceSession session(rt, JS::HeapState::MinorCollecting);
+    AutoSetThreadIsPerformingGC performingGC;
+    AutoStopVerifyingBarriers av(rt, false);
+    AutoDisableProxyCheck disableStrictProxyChecking(rt);
+    mozilla::DebugOnly<AutoEnterOOMUnsafeRegion> oomUnsafeRegion;
+
+    size_t initialNurserySize = spaceToEnd();
+
+    // Move objects pointed to by roots from the nursery to the major heap.
+    TenuringTracer mover(rt, this);
+
+    // Mark the store buffer. This must happen first.
+    StoreBuffer& sb = rt->gc.storeBuffer;
+
+    // The MIR graph only contains nursery pointers if cancelIonCompilations()
+    // is set on the store buffer, in which case we cancel all compilations.
+    maybeStartProfile(ProfileKey::CancelIonCompilations);
+    if (sb.cancelIonCompilations())
+        js::CancelOffThreadIonCompile(rt);
+    maybeEndProfile(ProfileKey::CancelIonCompilations);
+
+    maybeStartProfile(ProfileKey::TraceValues);
+    sb.traceValues(mover);
+    maybeEndProfile(ProfileKey::TraceValues);
+
+    maybeStartProfile(ProfileKey::TraceCells);
+    sb.traceCells(mover);
+    maybeEndProfile(ProfileKey::TraceCells);
+
+    maybeStartProfile(ProfileKey::TraceSlots);
+    sb.traceSlots(mover);
+    maybeEndProfile(ProfileKey::TraceSlots);
+
+    maybeStartProfile(ProfileKey::TraceWholeCells);
+    sb.traceWholeCells(mover);
+    maybeEndProfile(ProfileKey::TraceWholeCells);
+
+    maybeStartProfile(ProfileKey::TraceGenericEntries);
+    sb.traceGenericEntries(&mover);
+    maybeEndProfile(ProfileKey::TraceGenericEntries);
+
+    maybeStartProfile(ProfileKey::MarkRuntime);
+    rt->gc.traceRuntimeForMinorGC(&mover, session.lock);
+    maybeEndProfile(ProfileKey::MarkRuntime);
+
+    maybeStartProfile(ProfileKey::MarkDebugger);
+    {
+        gcstats::AutoPhase ap(rt->gc.stats, gcstats::PHASE_MARK_ROOTS);
+        Debugger::markAll(&mover);
+    }
+    maybeEndProfile(ProfileKey::MarkDebugger);
+
+    maybeStartProfile(ProfileKey::ClearNewObjectCache);
+    rt->contextFromMainThread()->caches.newObjectCache.clearNurseryObjects(rt);
+    maybeEndProfile(ProfileKey::ClearNewObjectCache);
+
+    // Most of the work is done here. This loop iterates over objects that have
+    // been moved to the major heap. If these objects have any outgoing pointers
+    // to the nursery, then those nursery objects get moved as well, until no
+    // objects are left to move. That is, we iterate to a fixed point.
+    maybeStartProfile(ProfileKey::CollectToFP);
+    collectToFixedPoint(mover, tenureCounts);
+    maybeEndProfile(ProfileKey::CollectToFP);
+
+    // Sweep compartments to update the array buffer object's view lists.
+    maybeStartProfile(ProfileKey::SweepArrayBufferViewList);
+    for (CompartmentsIter c(rt, SkipAtoms); !c.done(); c.next())
+        c->sweepAfterMinorGC(&mover);
+    maybeEndProfile(ProfileKey::SweepArrayBufferViewList);
+
+    // Update any slot or element pointers whose destination has been tenured.
+    maybeStartProfile(ProfileKey::UpdateJitActivations);
+    js::jit::UpdateJitActivationsForMinorGC(rt, &mover);
+    forwardedBuffers.finish();
+    maybeEndProfile(ProfileKey::UpdateJitActivations);
+
+    maybeStartProfile(ProfileKey::ObjectsTenuredCallback);
+    rt->gc.callObjectsTenuredCallback();
+    maybeEndProfile(ProfileKey::ObjectsTenuredCallback);
+
+    // Sweep.
+    maybeStartProfile(ProfileKey::FreeMallocedBuffers);
+    freeMallocedBuffers();
+    maybeEndProfile(ProfileKey::FreeMallocedBuffers);
+
+    maybeStartProfile(ProfileKey::Sweep);
+    sweep();
+    maybeEndProfile(ProfileKey::Sweep);
+
+    maybeStartProfile(ProfileKey::ClearStoreBuffer);
+    rt->gc.storeBuffer.clear();
+    maybeEndProfile(ProfileKey::ClearStoreBuffer);
+
+    // Make sure hashtables have been updated after the collection.
+    maybeStartProfile(ProfileKey::CheckHashTables);
+#ifdef JS_GC_ZEAL
+    if (rt->hasZealMode(ZealMode::CheckHashTablesOnMinorGC))
+        CheckHashTablesAfterMovingGC(rt);
+#endif
+    maybeEndProfile(ProfileKey::CheckHashTables);
+
+    // Calculate and return the promotion rate.
+    return mover.tenuredSize / double(initialNurserySize);
+}
+
+void
+js::Nursery::FreeMallocedBuffersTask::transferBuffersToFree(MallocedBuffersSet& buffersToFree,
+                                                            const AutoLockHelperThreadState& lock)
+{
+    // Transfer the contents of the source set to the task's buffers_ member by
+    // swapping the sets, which also clears the source.
+    MOZ_ASSERT(!isRunningWithLockHeld(lock));
+    MOZ_ASSERT(buffers_.empty());
+    mozilla::Swap(buffers_, buffersToFree);
+}
+
+void
+js::Nursery::FreeMallocedBuffersTask::run()
+{
+    for (MallocedBuffersSet::Range r = buffers_.all(); !r.empty(); r.popFront())
+        fop_->free_(r.front());
+    buffers_.clear();
+}
+
+void
+js::Nursery::freeMallocedBuffers()
+{
+    if (mallocedBuffers.empty())
+        return;
+
+    bool started;
+    {
+        AutoLockHelperThreadState lock;
+        freeMallocedBuffersTask->joinWithLockHeld(lock);
+        freeMallocedBuffersTask->transferBuffersToFree(mallocedBuffers, lock);
+        started = freeMallocedBuffersTask->startWithLockHeld(lock);
+    }
+
+    if (!started)
+        freeMallocedBuffersTask->runFromMainThread(runtime());
+
+    MOZ_ASSERT(mallocedBuffers.empty());
+}
+
+void
+js::Nursery::waitBackgroundFreeEnd()
+{
+    // We may finishRoots before nursery init if runtime init fails.
+    if (!isEnabled())
+        return;
+
+    MOZ_ASSERT(freeMallocedBuffersTask);
+    freeMallocedBuffersTask->join();
+}
+
+void
+js::Nursery::sweep()
+{
+    /* Sweep unique id's in all in-use chunks. */
+    for (CellsWithUniqueIdSet::Enum e(cellsWithUid_); !e.empty(); e.popFront()) {
+        JSObject* obj = static_cast<JSObject*>(e.front());
+        if (!IsForwarded(obj))
+            obj->zone()->removeUniqueId(obj);
+        else
+            MOZ_ASSERT(Forwarded(obj)->zone()->hasUniqueId(Forwarded(obj)));
+    }
+    cellsWithUid_.clear();
+
+    runSweepActions();
+    sweepDictionaryModeObjects();
+
+#ifdef JS_GC_ZEAL
+    /* Poison the nursery contents so touching a freed object will crash. */
+    for (unsigned i = 0; i < numChunks(); i++)
+        chunk(i).poisonAndInit(runtime(), JS_SWEPT_NURSERY_PATTERN);
+
+    if (runtime()->hasZealMode(ZealMode::GenerationalGC)) {
+        /* Only reset the alloc point when we are close to the end. */
+        if (currentChunk_ + 1 == numChunks())
+            setCurrentChunk(0);
+    } else
+#endif
+    {
+#ifdef JS_CRASH_DIAGNOSTICS
+        for (unsigned i = 0; i < numChunks(); ++i)
+            chunk(i).poisonAndInit(runtime(), JS_SWEPT_NURSERY_PATTERN);
+#endif
+        setCurrentChunk(0);
+    }
+
+    /* Set current start position for isEmpty checks. */
+    setStartPosition();
+    MemProfiler::SweepNursery(runtime());
+}
+
+size_t
+js::Nursery::spaceToEnd() const
+{
+    unsigned lastChunk = numChunks() - 1;
+
+    MOZ_ASSERT(lastChunk >= currentStartChunk_);
+    MOZ_ASSERT(currentStartPosition_ - chunk(currentStartChunk_).start() <= NurseryChunkUsableSize);
+
+    size_t bytes = (chunk(currentStartChunk_).end() - currentStartPosition_) +
+                   ((lastChunk - currentStartChunk_) * NurseryChunkUsableSize);
+
+    MOZ_ASSERT(bytes <= numChunks() * NurseryChunkUsableSize);
+
+    return bytes;
+}
+
+MOZ_ALWAYS_INLINE void
+js::Nursery::setCurrentChunk(unsigned chunkno)
+{
+    MOZ_ASSERT(chunkno < maxChunks());
+    MOZ_ASSERT(chunkno < numChunks());
+    currentChunk_ = chunkno;
+    position_ = chunk(chunkno).start();
+    currentEnd_ = chunk(chunkno).end();
+    chunk(chunkno).poisonAndInit(runtime(), JS_FRESH_NURSERY_PATTERN);
+}
+
+MOZ_ALWAYS_INLINE void
+js::Nursery::setStartPosition()
+{
+    currentStartChunk_ = currentChunk_;
+    currentStartPosition_ = position();
+}
+
+void
+js::Nursery::maybeResizeNursery(JS::gcreason::Reason reason, double promotionRate)
+{
+    static const double GrowThreshold   = 0.05;
+    static const double ShrinkThreshold = 0.01;
+
+    // Shrink the nursery to its minimum size of we ran out of memory or
+    // received a memory pressure event.
+    if (gc::IsOOMReason(reason)) {
+        minimizeAllocableSpace();
+        return;
+    }
+
+    if (promotionRate > GrowThreshold)
+        growAllocableSpace();
+    else if (promotionRate < ShrinkThreshold && previousPromotionRate_ < ShrinkThreshold)
+        shrinkAllocableSpace();
+
+    previousPromotionRate_ = promotionRate;
+}
+
+void
+js::Nursery::growAllocableSpace()
+{
+    updateNumChunks(Min(numChunks() * 2, maxNurseryChunks_));
+}
+
+void
+js::Nursery::shrinkAllocableSpace()
+{
+#ifdef JS_GC_ZEAL
+    if (runtime()->hasZealMode(ZealMode::GenerationalGC))
+        return;
+#endif
+    updateNumChunks(Max(numChunks() - 1, 1u));
+}
+
+void
+js::Nursery::minimizeAllocableSpace()
+{
+#ifdef JS_GC_ZEAL
+    if (runtime()->hasZealMode(ZealMode::GenerationalGC))
+        return;
+#endif
+    updateNumChunks(1);
+}
+
+void
+js::Nursery::updateNumChunks(unsigned newCount)
+{
+    if (numChunks() != newCount) {
+        AutoMaybeStartBackgroundAllocation maybeBgAlloc;
+        AutoLockGC lock(runtime());
+        updateNumChunksLocked(newCount, maybeBgAlloc, lock);
+    }
+}
+
+void
+js::Nursery::updateNumChunksLocked(unsigned newCount,
+                                   AutoMaybeStartBackgroundAllocation& maybeBgAlloc,
+                                   AutoLockGC& lock)
+{
+    // The GC nursery is an optimization and so if we fail to allocate nursery
+    // chunks we do not report an error.
+
+    unsigned priorCount = numChunks();
+    MOZ_ASSERT(priorCount != newCount);
+
+    if (newCount < priorCount) {
+        // Shrink the nursery and free unused chunks.
+        for (unsigned i = newCount; i < priorCount; i++)
+            runtime()->gc.recycleChunk(chunk(i).toChunk(runtime()), lock);
+        chunks_.shrinkTo(newCount);
+        return;
+    }
+
+    // Grow the nursery and allocate new chunks.
+    if (!chunks_.resize(newCount))
+        return;
+
+    for (unsigned i = priorCount; i < newCount; i++) {
+        auto newChunk = runtime()->gc.getOrAllocChunk(lock, maybeBgAlloc);
+        if (!newChunk) {
+            chunks_.shrinkTo(i);
+            return;
+        }
+
+        chunks_[i] = NurseryChunk::fromChunk(newChunk);
+        chunk(i).poisonAndInit(runtime(), JS_FRESH_NURSERY_PATTERN);
+    }
+}
+
+void
+js::Nursery::queueSweepAction(SweepThunk thunk, void* data)
+{
+    static_assert(sizeof(SweepAction) % CellSize == 0,
+                  "SweepAction size must be a multiple of cell size");
+
+    MOZ_ASSERT(isEnabled());
+
+    AutoEnterOOMUnsafeRegion oomUnsafe;
+    auto action = reinterpret_cast<SweepAction*>(allocate(sizeof(SweepAction)));
+    if (!action)
+        oomUnsafe.crash("Nursery::queueSweepAction");
+
+    new (action) SweepAction(thunk, data, sweepActions_);
+    sweepActions_ = action;
+}
+
+void
+js::Nursery::runSweepActions()
+{
+    // The hazard analysis doesn't know whether the thunks can GC.
+    JS::AutoSuppressGCAnalysis nogc;
+
+    AutoSetThreadIsSweeping threadIsSweeping;
+    for (auto action = sweepActions_; action; action = action->next)
+        action->thunk(action->data);
+    sweepActions_ = nullptr;
+}
+
+bool
+js::Nursery::queueDictionaryModeObjectToSweep(NativeObject* obj)
+{
+    MOZ_ASSERT(IsInsideNursery(obj));
+    return dictionaryModeObjects_.append(obj);
+}
+
+void
+js::Nursery::sweepDictionaryModeObjects()
+{
+    for (auto obj : dictionaryModeObjects_) {
+        if (!IsForwarded(obj))
+            obj->sweepDictionaryListPointer();
+    }
+    dictionaryModeObjects_.clear();
+}