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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* 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 */
* [SMDOC] GC Scheduling
* GC Scheduling Overview
* ======================
* Scheduling GC's in SpiderMonkey/Firefox is tremendously complicated because
* of the large number of subtle, cross-cutting, and widely dispersed factors
* that must be taken into account. A summary of some of the more important
* factors follows.
* Cost factors:
* * GC too soon and we'll revisit an object graph almost identical to the
* one we just visited; since we are unlikely to find new garbage, the
* traversal will be largely overhead. We rely heavily on external factors
* to signal us that we are likely to find lots of garbage: e.g. "a tab
* just got closed".
* * GC too late and we'll run out of memory to allocate (e.g. Out-Of-Memory,
* hereafter simply abbreviated to OOM). If this happens inside
* SpiderMonkey we may be able to recover, but most embedder allocations
* will simply crash on OOM, even if the GC has plenty of free memory it
* could surrender.
* * Memory fragmentation: if we fill the process with GC allocations, a
* request for a large block of contiguous memory may fail because no
* contiguous block is free, despite having enough memory available to
* service the request.
* * Management overhead: if our GC heap becomes large, we create extra
* overhead when managing the GC's structures, even if the allocations are
* mostly unused.
* Heap Management Factors:
* * GC memory: The GC has its own allocator that it uses to make fixed size
* allocations for GC managed things. In cases where the GC thing requires
* larger or variable sized memory to implement itself, it is responsible
* for using the system heap.
* * C Heap Memory: Rather than allowing for large or variable allocations,
* the SpiderMonkey GC allows GC things to hold pointers to C heap memory.
* It is the responsibility of the thing to free this memory with a custom
* finalizer (with the sole exception of NativeObject, which knows about
* slots and elements for performance reasons). C heap memory has different
* performance and overhead tradeoffs than GC internal memory, which need
* to be considered with scheduling a GC.
* Application Factors:
* * Most applications allocate heavily at startup, then enter a processing
* stage where memory utilization remains roughly fixed with a slower
* allocation rate. This is not always the case, however, so while we may
* optimize for this pattern, we must be able to handle arbitrary
* allocation patterns.
* Other factors:
* * Other memory: This is memory allocated outside the purview of the GC.
* Data mapped by the system for code libraries, data allocated by those
* libraries, data in the JSRuntime that is used to manage the engine,
* memory used by the embedding that is not attached to a GC thing, memory
* used by unrelated processes running on the hardware that use space we
* could otherwise use for allocation, etc. While we don't have to manage
* it, we do have to take it into account when scheduling since it affects
* when we will OOM.
* * Physical Reality: All real machines have limits on the number of bits
* that they are physically able to store. While modern operating systems
* can generally make additional space available with swapping, at some
* point there are simply no more bits to allocate. There is also the
* factor of address space limitations, particularly on 32bit machines.
* * Platform Factors: Each OS makes use of wildly different memory
* management techniques. These differences result in different performance
* tradeoffs, different fragmentation patterns, and different hard limits
* on the amount of physical and/or virtual memory that we can use before
* OOMing.
* Reasons for scheduling GC
* -------------------------
* While code generally takes the above factors into account in only an ad-hoc
* fashion, the API forces the user to pick a "reason" for the GC. We have a
* bunch of JS::GCReason reasons in GCAPI.h. These fall into a few categories
* that generally coincide with one or more of the above factors.
* Embedding reasons:
* 1) Do a GC now because the embedding knows something useful about the
* zone's memory retention state. These are GCReasons like LOAD_END,
* PAGE_HIDE, SET_NEW_DOCUMENT, DOM_UTILS. Mostly, Gecko uses these to
* indicate that a significant fraction of the scheduled zone's memory is
* probably reclaimable.
* 2) Do some known amount of GC work now because the embedding knows now is
* a good time to do a long, unblockable operation of a known duration.
* Correctness reasons:
* 3) Do a GC now because correctness depends on some GC property. For
* example, CC_WAITING is where the embedding requires the mark bits
* to be set correct. Also, EVICT_NURSERY where we need to work on the
* tenured heap.
* 4) Do a GC because we are shutting down: e.g. SHUTDOWN_CC or DESTROY_*.
* 5) Do a GC because a compartment was accessed between GC slices when we
* would have otherwise discarded it. We have to do a second GC to clean
* Emergency Reasons:
* 6) Do an all-zones, non-incremental GC now because the embedding knows it
* cannot wait: e.g. MEM_PRESSURE.
* 7) OOM when fetching a new Chunk results in a LAST_DITCH GC.
* Heap Size Limitation Reasons:
* 8) Do an incremental, zonal GC with reason MAYBEGC when we discover that
* the gc's allocated size is approaching the current trigger. This is
* called MAYBEGC because we make this check in the MaybeGC function.
* MaybeGC gets called at the top of the main event loop. Normally, it is
* expected that this callback will keep the heap size limited. It is
* relatively inexpensive, because it is invoked with no JS running and
* thus few stack roots to scan. For this reason, the GC's "trigger" bytes
* is less than the GC's "max" bytes as used by the trigger below.
* 9) Do an incremental, zonal GC with reason MAYBEGC when we go to allocate
* a new GC thing and find that the GC heap size has grown beyond the
* configured maximum (JSGC_MAX_BYTES). We trigger this GC by returning
* nullptr and then calling maybeGC at the top level of the allocator.
* This is then guaranteed to fail the "size greater than trigger" check
* above, since trigger is always less than max. After performing the GC,
* the allocator unconditionally returns nullptr to force an OOM exception
* is raised by the script.
* Note that this differs from a LAST_DITCH GC where we actually run out
* of memory (i.e., a call to a system allocator fails) when trying to
* allocate. Unlike above, LAST_DITCH GC only happens when we are really
* out of memory, not just when we cross an arbitrary trigger; despite
* this, it may still return an allocation at the end and allow the script
* to continue, if the LAST_DITCH GC was able to free up enough memory.
* 10) Do a GC under reason ALLOC_TRIGGER when we are over the GC heap trigger
* limit, but in the allocator rather than in a random call to maybeGC.
* This occurs if we allocate too much before returning to the event loop
* and calling maybeGC; this is extremely common in benchmarks and
* long-running Worker computations. Note that this uses a wildly
* different mechanism from the above in that it sets the interrupt flag
* and does the GC at the next loop head, before the next alloc, or
* maybeGC. The reason for this is that this check is made after the
* allocation and we cannot GC with an uninitialized thing in the heap.
* 11) Do an incremental, zonal GC with reason TOO_MUCH_MALLOC when the total
* amount of malloced memory is greater than the malloc trigger limit for the
* zone.
* Size Limitation Triggers Explanation
* ------------------------------------
* The GC internally is entirely unaware of the context of the execution of
* the mutator. It sees only:
* A) Allocated size: this is the amount of memory currently requested by the
* mutator. This quantity is monotonically increasing: i.e. the allocation
* rate is always >= 0. It is also easy for the system to track.
* B) Retained size: this is the amount of memory that the mutator can
* currently reach. Said another way, it is the size of the heap
* immediately after a GC (modulo background sweeping). This size is very
* costly to know exactly and also extremely hard to estimate with any
* fidelity.
* For reference, a common allocated vs. retained graph might look like:
* | ** **
* | ** ** * **
* | ** * ** * **
* | * ** * ** * **
* | ** ** * ** * **
* s| * * ** ** + + **
* i| * * * + + + + +
* z| * * * + + + + +
* e| * **+
* | * +
* | * +
* | * +
* | * +
* | * +
* |*+
* +--------------------------------------------------
* time
* *** = allocated
* +++ = retained
* Note that this is a bit of a simplification
* because in reality we track malloc and GC heap
* sizes separately and have a different level of
* granularity and accuracy on each heap.
* This presents some obvious implications for Mark-and-Sweep collectors.
* Namely:
* -> t[marking] ~= size[retained]
* -> t[sweeping] ~= size[allocated] - size[retained]
* In a non-incremental collector, maintaining low latency and high
* responsiveness requires that total GC times be as low as possible. Thus,
* in order to stay responsive when we did not have a fully incremental
* collector, our GC triggers were focused on minimizing collection time.
* Furthermore, since size[retained] is not under control of the GC, all the
* GC could do to control collection times was reduce sweep times by
* minimizing size[allocated], per the equation above.
* The result of the above is GC triggers that focus on size[allocated] to
* the exclusion of other important factors and default heuristics that are
* not optimal for a fully incremental collector. On the other hand, this is
* not all bad: minimizing size[allocated] also minimizes the chance of OOM
* and sweeping remains one of the hardest areas to further incrementalize.
* -------------------
* Occurs when we return to the event loop and find our heap is getting
* largish, but before t[marking] OR t[sweeping] is too large for a
* responsive non-incremental GC. This is intended to be the common case
* in normal web applications: e.g. we just finished an event handler and
* the few objects we allocated when computing the new whatzitz have
* pushed us slightly over the limit. After this GC we rescale the new
* EAGER_ALLOC_TRIGGER trigger to 150% of size[retained] so that our
* non-incremental GC times will always be proportional to this size
* rather than being dominated by sweeping.
* As a concession to mutators that allocate heavily during their startup
* phase, we have a highFrequencyGCMode that ups the growth rate to 300%
* of the current size[retained] so that we'll do fewer longer GCs at the
* end of the mutator startup rather than more, smaller GCs.
* Assumptions:
* -> Responsiveness is proportional to t[marking] + t[sweeping].
* -> size[retained] is proportional only to GC allocations.
* ALLOC_TRIGGER (non-incremental)
* -------------------------------
* If we do not return to the event loop before getting all the way to our
* gc trigger bytes then MAYBEGC will never fire. To avoid OOMing, we
* succeed the current allocation and set the script interrupt so that we
* will (hopefully) do a GC before we overflow our max and have to raise
* an OOM exception for the script.
* Assumptions:
* -> Common web scripts will return to the event loop before using
* 10% of the current triggerBytes worth of GC memory.
* ALLOC_TRIGGER (incremental)
* ---------------------------
* In practice the above trigger is rough: if a website is just on the
* cusp, sometimes it will trigger a non-incremental GC moments before
* returning to the event loop, where it could have done an incremental
* GC. Thus, we recently added an incremental version of the above with a
* substantially lower threshold, so that we have a soft limit here. If
* IGC can collect faster than the allocator generates garbage, even if
* the allocator does not return to the event loop frequently, we should
* not have to fall back to a non-incremental GC.
* --------------------
* Do a full, non-incremental GC if we overflow ALLOC_TRIGGER during an
* incremental GC. When in the middle of an incremental GC, we suppress
* our other triggers, so we need a way to backstop the IGC if the
* mutator allocates faster than the IGC can clean things up.
* ---------------
* Performs a GC before size[allocated] - size[retained] gets too large
* for non-incremental sweeping to be fast in the case that we have
* significantly more malloc allocation than GC allocation. This is meant
* to complement MAYBEGC triggers. We track this by counting malloced
* bytes; the counter gets reset at every GC since we do not always have a
* size at the time we call free. Because of this, the malloc heuristic
* is, unfortunately, not usefully able to augment our other GC heap
* triggers and is limited to this singular heuristic.
* Assumptions:
* -> EITHER size[allocated_by_malloc] ~= size[allocated_by_GC]
* OR time[sweeping] ~= size[allocated_by_malloc]
* -> size[retained] @ t0 ~= size[retained] @ t1
* i.e. That the mutator is in steady-state operation.
* -------------
* Does a GC because we are out of memory.
* Assumptions:
* -> size[retained] < size[available_memory]
#ifndef gc_Scheduling_h
#define gc_Scheduling_h
#include "mozilla/Atomics.h"
#include "mozilla/DebugOnly.h"
#include "gc/GCEnum.h"
#include "js/AllocPolicy.h"
#include "js/GCAPI.h"
#include "js/HashTable.h"
#include "js/HeapAPI.h"
#include "js/SliceBudget.h"
#include "threading/ProtectedData.h"
namespace js {
class AutoLockGC;
class ZoneAllocator;
class ZoneAllocPolicy;
namespace gc {
struct Cell;
* Default settings for tuning the GC. Some of these can be set at runtime,
* This list is not complete, some tuning parameters are not listed here.
* If you change the values here, please also consider changing them in
* modules/libpref/init/all.js where they are duplicated for the Firefox
* preferences.
namespace TuningDefaults {
static const size_t GCZoneAllocThresholdBase = 27 * 1024 * 1024;
* With some testing (Bug 1532838) we increased this to 256K from 192K
* which improves performance. We should try to reduce this for background
* tabs.
static const size_t GCMinNurseryBytes = 256 * 1024;
* This must be greater than 1.3 to maintain performance on splay-latency.
static const double SmallHeapIncrementalLimit = 1.40;
static const double LargeHeapIncrementalLimit = 1.10;
static const size_t ZoneAllocDelayBytes = 1024 * 1024;
static const auto HighFrequencyThreshold = 1; // in seconds
static const size_t SmallHeapSizeMaxBytes = 100 * 1024 * 1024;
static const size_t LargeHeapSizeMinBytes = 500 * 1024 * 1024;
static const double HighFrequencySmallHeapGrowth = 3.0;
static const double HighFrequencyLargeHeapGrowth = 1.5;
static const double LowFrequencyHeapGrowth = 1.5;
static const uint32_t MinEmptyChunkCount = 1;
static const uint32_t MaxEmptyChunkCount = 30;
static const int64_t DefaultTimeBudgetMS = SliceBudget::UnlimitedTimeBudget;
static const bool CompactingEnabled = true;
static const bool IncrementalWeakMapMarkingEnabled = true;
static const uint32_t NurseryFreeThresholdForIdleCollection = ChunkSize / 4;
static const double NurseryFreeThresholdForIdleCollectionFraction = 0.25;
static const double PretenureThreshold = 0.6;
static const double PretenureGroupThreshold = 3000;
static const auto MinLastDitchGCPeriod = 60; // in seconds
static const size_t MallocThresholdBase = 38 * 1024 * 1024;
static const double MallocGrowthFactor = 1.5;
static const double HelperThreadRatio = 0.5;
static const size_t MaxHelperThreads = 8;
} // namespace TuningDefaults
* Encapsulates all of the GC tunables. These are effectively constant and
* should only be modified by setParameter.
class GCSchedulingTunables {
* Maximum nominal heap before last ditch GC.
UnprotectedData<size_t> gcMaxBytes_;
* Minimum and maximum nursery size for each runtime.
MainThreadData<size_t> gcMinNurseryBytes_;
MainThreadData<size_t> gcMaxNurseryBytes_;
* The base value used to compute zone->threshold.bytes(). When
* gcHeapSize.bytes() exceeds threshold.bytes() for a zone, the zone may be
* scheduled for a GC, depending on the exact circumstances.
MainThreadOrGCTaskData<size_t> gcZoneAllocThresholdBase_;
* Multiple of threshold.bytes() which triggers a non-incremental GC.
UnprotectedData<double> smallHeapIncrementalLimit_;
* Multiple of threshold.bytes() which triggers a non-incremental GC.
UnprotectedData<double> largeHeapIncrementalLimit_;
* Number of bytes to allocate between incremental slices in GCs triggered by
* the zone allocation threshold.
* This value does not have a JSGCParamKey parameter yet.
UnprotectedData<size_t> zoneAllocDelayBytes_;
* We enter high-frequency mode if we GC a twice within this many
* microseconds.
MainThreadOrGCTaskData<mozilla::TimeDuration> highFrequencyThreshold_;
* When in the |highFrequencyGC| mode, these parameterize the per-zone
* "HeapGrowthFactor" computation.
MainThreadOrGCTaskData<size_t> smallHeapSizeMaxBytes_;
MainThreadOrGCTaskData<size_t> largeHeapSizeMinBytes_;
MainThreadOrGCTaskData<double> highFrequencySmallHeapGrowth_;
MainThreadOrGCTaskData<double> highFrequencyLargeHeapGrowth_;
* When not in |highFrequencyGC| mode, this is the global (stored per-zone)
* "HeapGrowthFactor".
MainThreadOrGCTaskData<double> lowFrequencyHeapGrowth_;
* Controls the number of empty chunks reserved for future allocation.
UnprotectedData<uint32_t> minEmptyChunkCount_;
UnprotectedData<uint32_t> maxEmptyChunkCount_;
* Attempt to run a minor GC in the idle time if the free space falls
* below this threshold. The absolute threshold is used when the nursery is
* large and the percentage when it is small. See Nursery::shouldCollect()
UnprotectedData<uint32_t> nurseryFreeThresholdForIdleCollection_;
UnprotectedData<double> nurseryFreeThresholdForIdleCollectionFraction_;
* Fraction of objects tenured to trigger pretenuring (between 0 and 1). If
* this fraction is met, the GC proceeds to calculate which objects will be
* tenured. If this is 1.0f (actually if it is not < 1.0f) then pretenuring
* is disabled.
UnprotectedData<double> pretenureThreshold_;
* During a single nursery collection, if this many objects from the same
* object group are tenured, then that group will be pretenured.
UnprotectedData<uint32_t> pretenureGroupThreshold_;
* Last ditch GC is skipped if allocation failure occurs less than this many
* seconds from the previous one.
MainThreadData<mozilla::TimeDuration> minLastDitchGCPeriod_;
* The base value used to compute the GC trigger for malloc allocated memory.
MainThreadOrGCTaskData<size_t> mallocThresholdBase_;
* Malloc memory growth factor.
MainThreadOrGCTaskData<double> mallocGrowthFactor_;
size_t gcMaxBytes() const { return gcMaxBytes_; }
size_t gcMinNurseryBytes() const { return gcMinNurseryBytes_; }
size_t gcMaxNurseryBytes() const { return gcMaxNurseryBytes_; }
size_t gcZoneAllocThresholdBase() const { return gcZoneAllocThresholdBase_; }
double smallHeapIncrementalLimit() const {
return smallHeapIncrementalLimit_;
double largeHeapIncrementalLimit() const {
return largeHeapIncrementalLimit_;
size_t zoneAllocDelayBytes() const { return zoneAllocDelayBytes_; }
const mozilla::TimeDuration& highFrequencyThreshold() const {
return highFrequencyThreshold_;
size_t smallHeapSizeMaxBytes() const { return smallHeapSizeMaxBytes_; }
size_t largeHeapSizeMinBytes() const { return largeHeapSizeMinBytes_; }
double highFrequencySmallHeapGrowth() const {
return highFrequencySmallHeapGrowth_;
double highFrequencyLargeHeapGrowth() const {
return highFrequencyLargeHeapGrowth_;
double lowFrequencyHeapGrowth() const { return lowFrequencyHeapGrowth_; }
unsigned minEmptyChunkCount(const AutoLockGC&) const {
return minEmptyChunkCount_;
unsigned maxEmptyChunkCount() const { return maxEmptyChunkCount_; }
uint32_t nurseryFreeThresholdForIdleCollection() const {
return nurseryFreeThresholdForIdleCollection_;
double nurseryFreeThresholdForIdleCollectionFraction() const {
return nurseryFreeThresholdForIdleCollectionFraction_;
bool attemptPretenuring() const { return pretenureThreshold_ < 1.0; }
double pretenureThreshold() const { return pretenureThreshold_; }
uint32_t pretenureGroupThreshold() const { return pretenureGroupThreshold_; }
mozilla::TimeDuration minLastDitchGCPeriod() const {
return minLastDitchGCPeriod_;
size_t mallocThresholdBase() const { return mallocThresholdBase_; }
double mallocGrowthFactor() const { return mallocGrowthFactor_; }
MOZ_MUST_USE bool setParameter(JSGCParamKey key, uint32_t value,
const AutoLockGC& lock);
void resetParameter(JSGCParamKey key, const AutoLockGC& lock);
void setSmallHeapSizeMaxBytes(size_t value);
void setLargeHeapSizeMinBytes(size_t value);
void setHighFrequencySmallHeapGrowth(double value);
void setHighFrequencyLargeHeapGrowth(double value);
void setLowFrequencyHeapGrowth(double value);
void setMinEmptyChunkCount(uint32_t value);
void setMaxEmptyChunkCount(uint32_t value);
class GCSchedulingState {
* Influences how we schedule and run GC's in several subtle ways. The most
* important factor is in how it controls the "HeapGrowthFactor". The
* growth factor is a measure of how large (as a percentage of the last GC)
* the heap is allowed to grow before we try to schedule another GC.
MainThreadOrGCTaskData<bool> inHighFrequencyGCMode_;
* Influences the GC thresholds for the atoms zone to discourage collection of
* this zone during page load.
MainThreadOrGCTaskData<bool> inPageLoad;
GCSchedulingState() : inHighFrequencyGCMode_(false) {}
bool inHighFrequencyGCMode() const { return inHighFrequencyGCMode_; }
void updateHighFrequencyMode(const mozilla::TimeStamp& lastGCTime,
const mozilla::TimeStamp& currentTime,
const GCSchedulingTunables& tunables) {
inHighFrequencyGCMode_ =
!lastGCTime.IsNull() &&
lastGCTime + tunables.highFrequencyThreshold() > currentTime;
enum class TriggerKind { None, Incremental, NonIncremental };
struct TriggerResult {
TriggerKind kind;
size_t usedBytes;
size_t thresholdBytes;
using AtomicByteCount = mozilla::Atomic<size_t, mozilla::ReleaseAcquire>;
* Tracks the size of allocated data. This is used for both GC and malloc data.
* It automatically maintains the memory usage relationship between parent and
* child instances, i.e. between those in a GCRuntime and its Zones.
class HeapSize {
* An instance that contains our parent's heap usage, or null if this is the
* top-level usage container.
HeapSize* const parent_;
* The number of bytes in use. For GC heaps this is approximate to the nearest
* ArenaSize. It is atomic because it is updated by both the active and GC
* helper threads.
AtomicByteCount bytes_;
* The number of bytes retained after the last collection. This is updated
* dynamically during incremental GC. It does not include allocations that
* happen during a GC.
AtomicByteCount retainedBytes_;
explicit HeapSize(HeapSize* parent) : parent_(parent), bytes_(0) {}
size_t bytes() const { return bytes_; }
size_t retainedBytes() const { return retainedBytes_; }
void updateOnGCStart() { retainedBytes_ = size_t(bytes_); }
void addGCArena() { addBytes(ArenaSize); }
void removeGCArena() {
MOZ_ASSERT(retainedBytes_ >= ArenaSize);
removeBytes(ArenaSize, true /* only sweeping removes arenas */);
void addBytes(size_t nbytes) {
mozilla::DebugOnly<size_t> initialBytes(bytes_);
MOZ_ASSERT(initialBytes + nbytes > initialBytes);
bytes_ += nbytes;
if (parent_) {
void removeBytes(size_t nbytes, bool wasSwept) {
if (wasSwept) {
// TODO: We would like to assert that retainedBytes_ >= nbytes is here but
// we can't do that yet, so clamp the result to zero.
retainedBytes_ = nbytes <= retainedBytes_ ? retainedBytes_ - nbytes : 0;
MOZ_ASSERT(bytes_ >= nbytes);
bytes_ -= nbytes;
if (parent_) {
parent_->removeBytes(nbytes, wasSwept);
/* Pair to adoptArenas. Adopts the attendant usage statistics. */
void adopt(HeapSize& source) {
// Skip retainedBytes_: we never adopt zones that are currently being
// collected.
bytes_ += source.bytes_;
source.retainedBytes_ = 0;
source.bytes_ = 0;
// Heap size thresholds used to trigger GC. This is an abstract base class for
// GC heap and malloc thresholds defined below.
class HeapThreshold {
: startBytes_(SIZE_MAX),
sliceBytes_(SIZE_MAX) {}
// The threshold at which to start a new incremental collection.
// TODO: This is currently read off-thread during parsing, but at some point
// we should be able to make this MainThreadData<>.
AtomicByteCount startBytes_;
// The threshold at which start a new non-incremental collection or finish an
// ongoing collection non-incrementally.
size_t incrementalLimitBytes_;
// The threshold at which to trigger a slice during an ongoing incremental
// collection.
size_t sliceBytes_;
size_t startBytes() const { return startBytes_; }
size_t sliceBytes() const { return sliceBytes_; }
size_t incrementalLimitBytes() const { return incrementalLimitBytes_; }
double eagerAllocTrigger(bool highFrequencyGC) const;
void setSliceThreshold(ZoneAllocator* zone, const HeapSize& heapSize,
const GCSchedulingTunables& tunables);
void clearSliceThreshold() { sliceBytes_ = SIZE_MAX; }
bool hasSliceThreshold() const { return sliceBytes_ != SIZE_MAX; }
void setIncrementalLimitFromStartBytes(size_t retainedBytes,
const GCSchedulingTunables& tunables);
// A heap threshold that is based on a multiple of the retained size after the
// last collection adjusted based on collection frequency and retained
// size. This is used to determine when to do a zone GC based on GC heap size.
class GCHeapThreshold : public HeapThreshold {
void updateStartThreshold(size_t lastBytes, JSGCInvocationKind gckind,
const GCSchedulingTunables& tunables,
const GCSchedulingState& state, bool isAtomsZone,
const AutoLockGC& lock);
static double computeZoneHeapGrowthFactorForHeapSize(
size_t lastBytes, const GCSchedulingTunables& tunables,
const GCSchedulingState& state);
static size_t computeZoneTriggerBytes(double growthFactor, size_t lastBytes,
JSGCInvocationKind gckind,
const GCSchedulingTunables& tunables,
const AutoLockGC& lock);
// A heap threshold that is calculated as a constant multiple of the retained
// size after the last collection. This is used to determines when to do a zone
// GC based on malloc data.
class MallocHeapThreshold : public HeapThreshold {
void updateStartThreshold(size_t lastBytes,
const GCSchedulingTunables& tunables,
const AutoLockGC& lock);
static size_t computeZoneTriggerBytes(double growthFactor, size_t lastBytes,
size_t baseBytes,
const AutoLockGC& lock);
// A fixed threshold that's used to determine when we need to do a zone GC based
// on allocated JIT code.
class JitHeapThreshold : public HeapThreshold {
explicit JitHeapThreshold(size_t bytes) { startBytes_ = bytes; }
struct SharedMemoryUse {
explicit SharedMemoryUse(MemoryUse use) : count(0), nbytes(0) {
#ifdef DEBUG
this->use = use;
size_t count;
size_t nbytes;
#ifdef DEBUG
MemoryUse use;
// A map which tracks shared memory uses (shared in the sense that an allocation
// can be referenced by more than one GC thing in a zone). This allows us to
// only account for the memory once.
using SharedMemoryMap =
HashMap<void*, SharedMemoryUse, DefaultHasher<void*>, SystemAllocPolicy>;
#ifdef DEBUG
// Counts memory associated with GC things in a zone.
// This records details of the cell (or non-cell pointer) the memory allocation
// is associated with to check the correctness of the information provided. This
// is not present in opt builds.
class MemoryTracker {
void fixupAfterMovingGC();
void checkEmptyOnDestroy();
void adopt(MemoryTracker& other);
// Track memory by associated GC thing pointer.
void trackGCMemory(Cell* cell, size_t nbytes, MemoryUse use);
void untrackGCMemory(Cell* cell, size_t nbytes, MemoryUse use);
void swapGCMemory(Cell* a, Cell* b, MemoryUse use);
// Track memory by associated non-GC thing pointer.
void registerNonGCMemory(void* ptr, MemoryUse use);
void unregisterNonGCMemory(void* ptr, MemoryUse use);
void moveNonGCMemory(void* dst, void* src, MemoryUse use);
void incNonGCMemory(void* ptr, size_t nbytes, MemoryUse use);
void decNonGCMemory(void* ptr, size_t nbytes, MemoryUse use);
template <typename Ptr>
struct Key {
Key(Ptr* ptr, MemoryUse use);
Ptr* ptr() const;
MemoryUse use() const;
# ifdef JS_64BIT
// Pack this into a single word on 64 bit platforms.
uintptr_t ptr_ : 56;
uintptr_t use_ : 8;
# else
uintptr_t ptr_ : 32;
uintptr_t use_ : 8;
# endif
template <typename Ptr>
struct Hasher {
using KeyT = Key<Ptr>;
using Lookup = KeyT;
static HashNumber hash(const Lookup& l);
static bool match(const KeyT& key, const Lookup& l);
static void rekey(KeyT& k, const KeyT& newKey);
template <typename Ptr>
using Map = HashMap<Key<Ptr>, size_t, Hasher<Ptr>, SystemAllocPolicy>;
using GCMap = Map<Cell>;
using NonGCMap = Map<void>;
static bool isGCMemoryUse(MemoryUse use);
static bool isNonGCMemoryUse(MemoryUse use);
static bool allowMultipleAssociations(MemoryUse use);
size_t getAndRemoveEntry(const Key<Cell>& key, LockGuard<Mutex>& lock);
Mutex mutex;
// Map containing the allocated size associated with (cell, use) pairs.
GCMap gcMap;
// Map containing the allocated size associated (non-cell pointer, use) pairs.
NonGCMap nonGCMap;
#endif // DEBUG
static inline double LinearInterpolate(double x, double x0, double y0,
double x1, double y1) {
MOZ_ASSERT(x0 < x1);
if (x < x0) {
return y0;
if (x < x1) {
return y0 + (y1 - y0) * ((x - x0) / (x1 - x0));
return y1;
} // namespace gc
} // namespace js
#endif // gc_Scheduling_h