Source code
Revision control
Copy as Markdown
Other Tools
/* -*- 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
/*
* [SMDOC] GC Scheduling
*
* GC Scheduling Overview
* ======================
*
* See also GC scheduling from Firefox's perspective here:
*
* 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.
* These are INTER_SLICE_GC and REFRESH_FRAME.
*
* Correctness reasons:
*
* 3) Do a GC now because correctness depends on some GC property. For
* example, CC_FORCED is where the embedding requires the mark bits to be
* set correctly. 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
* it up: e.g. COMPARTMENT_REVIVED.
*
* 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.
*
* EAGER_ALLOC_TRIGGER
* -------------------
* 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.
*
* INCREMENTAL_TOO_SLOW
* --------------------
* 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.
*
* TOO_MUCH_MALLOC
* ---------------
* 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.
*
* LAST_DITCH_GC
* -------------
* 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 "mozilla/Maybe.h"
#include "mozilla/TimeStamp.h"
#include "gc/GCEnum.h"
#include "js/AllocPolicy.h"
#include "js/GCAPI.h"
#include "js/HashTable.h"
#include "js/HeapAPI.h"
#include "threading/ProtectedData.h"
// Macro to define scheduling tunables for GC parameters. Expands its argument
// repeatedly with the following arguments:
// - key: the JSGCParamKey value for this parameter
// - type: the storage type
// - name: the name of GCSchedulingTunables getter method
// - convert: a helper class defined in Scheduling.cpp that provides
// conversion methods
// - check: a helper function defined in Scheduling.cppto check the value is
// valid
// - default: the initial value and that assigned by resetParameter
#define FOR_EACH_GC_TUNABLE(_) \
/* \
* JSGC_MAX_BYTES \
* \
* Maximum nominal heap before last ditch GC. \
*/ \
_(JSGC_MAX_BYTES, size_t, gcMaxBytes, ConvertSize, NoCheck, 0xffffffff) \
\
/* \
* JSGC_MIN_NURSERY_BYTES \
* JSGC_MAX_NURSERY_BYTES \
* \
* Minimum and maximum nursery size for each runtime. \
*/ \
_(JSGC_MIN_NURSERY_BYTES, size_t, gcMinNurseryBytes, ConvertNurseryBytes, \
CheckNurserySize, 256 * 1024) \
_(JSGC_MAX_NURSERY_BYTES, size_t, gcMaxNurseryBytes, ConvertNurseryBytes, \
CheckNurserySize, JS::DefaultNurseryMaxBytes) \
\
/* \
* JSGC_ALLOCATION_THRESHOLD \
* \
* \
* 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. \
*/ \
_(JSGC_ALLOCATION_THRESHOLD, size_t, gcZoneAllocThresholdBase, ConvertMB, \
NoCheck, 27 * 1024 * 1024) \
\
/* \
* JSGC_SMALL_HEAP_SIZE_MAX \
* JSGC_LARGE_HEAP_SIZE_MIN \
* \
* Used to classify heap sizes into one of small, medium or large. This \
* affects the calcuation of the incremental GC trigger and the heap growth \
* factor in high frequency GC mode. \
*/ \
_(JSGC_SMALL_HEAP_SIZE_MAX, size_t, smallHeapSizeMaxBytes, ConvertMB, \
NoCheck, 100 * 1024 * 1024) \
_(JSGC_LARGE_HEAP_SIZE_MIN, size_t, largeHeapSizeMinBytes, ConvertMB, \
CheckNonZero, 500 * 1024 * 1024) \
\
/* \
* JSGC_SMALL_HEAP_INCREMENTAL_LIMIT \
* JSGC_LARGE_HEAP_INCREMENTAL_LIMIT \
* \
* Multiple of threshold.bytes() which triggers a non-incremental GC. \
* \
* The small heap limit must be greater than 1.3 to maintain performance on \
* splay-latency. \
*/ \
_(JSGC_SMALL_HEAP_INCREMENTAL_LIMIT, double, smallHeapIncrementalLimit, \
ConvertTimes100, CheckIncrementalLimit, 1.50) \
_(JSGC_LARGE_HEAP_INCREMENTAL_LIMIT, double, largeHeapIncrementalLimit, \
ConvertTimes100, CheckIncrementalLimit, 1.10) \
\
/* \
* JSGC_HIGH_FREQUENCY_TIME_LIMIT \
* \
* We enter high-frequency mode if we GC a twice within this many \
* millisconds. \
*/ \
_(JSGC_HIGH_FREQUENCY_TIME_LIMIT, mozilla::TimeDuration, \
highFrequencyThreshold, ConvertMillis, NoCheck, \
mozilla::TimeDuration::FromSeconds(1)) \
\
/* \
* JSGC_LOW_FREQUENCY_HEAP_GROWTH \
* \
* When not in |highFrequencyGC| mode, this is the global (stored per-zone) \
* "HeapGrowthFactor". \
*/ \
_(JSGC_LOW_FREQUENCY_HEAP_GROWTH, double, lowFrequencyHeapGrowth, \
ConvertTimes100, CheckHeapGrowth, 1.5) \
\
/* \
* JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH \
* JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH \
* \
* When in the |highFrequencyGC| mode, these parameterize the per-zone \
* "HeapGrowthFactor" computation. \
*/ \
_(JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH, double, \
highFrequencySmallHeapGrowth, ConvertTimes100, CheckHeapGrowth, 3.0) \
_(JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH, double, \
highFrequencyLargeHeapGrowth, ConvertTimes100, CheckHeapGrowth, 1.5) \
\
/* \
* JSGC_MALLOC_THRESHOLD_BASE \
* \
* The base value used to compute the GC trigger for malloc allocated \
* memory. \
*/ \
_(JSGC_MALLOC_THRESHOLD_BASE, size_t, mallocThresholdBase, ConvertMB, \
NoCheck, 38 * 1024 * 1024) \
\
/* \
* Number of bytes to allocate between incremental slices in GCs triggered \
* by the zone allocation threshold. \
*/ \
_(JSGC_ZONE_ALLOC_DELAY_KB, size_t, zoneAllocDelayBytes, ConvertKB, \
CheckNonZero, 1024 * 1024) \
\
/* \
* JSGC_URGENT_THRESHOLD_MB \
* \
* The point before reaching the non-incremental limit at which to start \
* increasing the slice budget and frequency of allocation triggered slices. \
*/ \
_(JSGC_URGENT_THRESHOLD_MB, size_t, urgentThresholdBytes, ConvertMB, \
NoCheck, 16 * 1024 * 1024) \
\
/* \
* JSGC_NURSERY_EAGER_COLLECTION_THRESHOLD_KB \
* JSGC_NURSERY_EAGER_COLLECTION_THRESHOLD_PERCENT \
* JSGC_NURSERY_EAGER_COLLECTION_TIMEOUT_MS \
* \
* JS::MaybeRunNurseryCollection will run a minor GC if the free space falls \
* below a threshold or if it hasn't been collected for too long. \
* \
* To avoid making this too eager, two thresholds must be met. The free \
* space must fall below a size threshold and the fraction of free space \
* remaining must also fall below a threshold. \
* \
* See Nursery::wantEagerCollection() for more details. \
*/ \
_(JSGC_NURSERY_EAGER_COLLECTION_THRESHOLD_KB, size_t, \
nurseryEagerCollectionThresholdBytes, ConvertKB, NoCheck, ChunkSize / 4) \
_(JSGC_NURSERY_EAGER_COLLECTION_THRESHOLD_PERCENT, double, \
nurseryEagerCollectionThresholdPercent, ConvertTimes100, \
CheckNonZeroUnitRange, 0.25) \
_(JSGC_NURSERY_EAGER_COLLECTION_TIMEOUT_MS, mozilla::TimeDuration, \
nurseryEagerCollectionTimeout, ConvertMillis, NoCheck, \
mozilla::TimeDuration::FromSeconds(5)) \
\
/* \
* JSGC_BALANCED_HEAP_LIMITS_ENABLED \
* JSGC_HEAP_GROWTH_FACTOR \
*/ \
_(JSGC_BALANCED_HEAP_LIMITS_ENABLED, bool, balancedHeapLimitsEnabled, \
ConvertBool, NoCheck, false) \
_(JSGC_HEAP_GROWTH_FACTOR, double, heapGrowthFactor, ConvertDouble, NoCheck, \
50.0) \
\
/* \
* JSGC_MIN_LAST_DITCH_GC_PERIOD \
* \
* Last ditch GC is skipped if allocation failure occurs less than this many \
* seconds from the previous one. \
*/ \
_(JSGC_MIN_LAST_DITCH_GC_PERIOD, mozilla::TimeDuration, \
minLastDitchGCPeriod, ConvertSeconds, NoCheck, \
TimeDuration::FromSeconds(60)) \
\
/* \
* JSGC_PARALLEL_MARKING_THRESHOLD_MB \
*/ \
_(JSGC_PARALLEL_MARKING_THRESHOLD_MB, size_t, parallelMarkingThresholdBytes, \
ConvertMB, NoCheck, 4 * 1024 * 1024)
namespace js {
class ZoneAllocator;
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 {
/* JSGC_MIN_EMPTY_CHUNK_COUNT */
static const uint32_t MinEmptyChunkCount = 1;
/* JSGC_MAX_EMPTY_CHUNK_COUNT */
static const uint32_t MaxEmptyChunkCount = 30;
/* JSGC_SLICE_TIME_BUDGET_MS */
static const int64_t DefaultTimeBudgetMS = 0; // Unlimited by default.
/* JSGC_INCREMENTAL_GC_ENABLED */
static const bool IncrementalGCEnabled = false;
/* JSGC_PER_ZONE_GC_ENABLED */
static const bool PerZoneGCEnabled = false;
/* JSGC_COMPACTING_ENABLED */
static const bool CompactingEnabled = true;
/* JSGC_PARALLEL_MARKING_ENABLED */
static const bool ParallelMarkingEnabled = false;
/* JSGC_INCREMENTAL_WEAKMAP_ENABLED */
static const bool IncrementalWeakMapMarkingEnabled = true;
/* JSGC_SEMISPACE_NURSERY_ENABLED */
static const bool SemispaceNurseryEnabled = false;
/* JSGC_HELPER_THREAD_RATIO */
static const double HelperThreadRatio = 0.5;
/* JSGC_MAX_HELPER_THREADS */
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 {
#define DEFINE_TUNABLE_FIELD(key, type, name, convert, check, default) \
MainThreadOrGCTaskData<type> name##_;
FOR_EACH_GC_TUNABLE(DEFINE_TUNABLE_FIELD)
#undef DEFINE_TUNABLE_FIELD
public:
GCSchedulingTunables();
#define DEFINE_TUNABLE_ACCESSOR(key, type, name, convert, check, default) \
type name() const { return name##_; }
FOR_EACH_GC_TUNABLE(DEFINE_TUNABLE_ACCESSOR)
#undef DEFINE_TUNABLE_ACCESSOR
uint32_t getParameter(JSGCParamKey key);
[[nodiscard]] bool setParameter(JSGCParamKey key, uint32_t value);
void resetParameter(JSGCParamKey key);
private:
void maintainInvariantsAfterUpdate(JSGCParamKey updated);
void checkInvariants();
};
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.
*/
mozilla::Atomic<bool, mozilla::ReleaseAcquire> inHighFrequencyGCMode_;
public:
GCSchedulingState() : inHighFrequencyGCMode_(false) {}
bool inHighFrequencyGCMode() const { return inHighFrequencyGCMode_; }
void updateHighFrequencyMode(const mozilla::TimeStamp& lastGCTime,
const mozilla::TimeStamp& currentTime,
const GCSchedulingTunables& tunables);
void updateHighFrequencyModeForReason(JS::GCReason reason);
};
struct TriggerResult {
bool shouldTrigger;
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 {
/*
* 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 in use at the start of the last collection.
*/
MainThreadData<size_t> initialBytes_;
/*
* 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_;
public:
explicit HeapSize() {
MOZ_ASSERT(bytes_ == 0);
MOZ_ASSERT(retainedBytes_ == 0);
}
size_t bytes() const { return bytes_; }
size_t initialBytes() const { return initialBytes_; }
size_t retainedBytes() const { return retainedBytes_; }
void updateOnGCStart() { retainedBytes_ = initialBytes_ = bytes(); }
void addGCArena() { addBytes(ArenaSize); }
void removeGCArena() {
MOZ_ASSERT(retainedBytes_ >= ArenaSize);
removeBytes(ArenaSize, true /* only sweeping removes arenas */);
MOZ_ASSERT(retainedBytes_ <= bytes_);
}
void addBytes(size_t nbytes) {
mozilla::DebugOnly<size_t> initialBytes(bytes_);
MOZ_ASSERT(initialBytes + nbytes > initialBytes);
bytes_ += nbytes;
}
void removeBytes(size_t nbytes, bool updateRetainedSize) {
if (updateRetainedSize) {
MOZ_ASSERT(retainedBytes_ >= nbytes);
retainedBytes_ -= nbytes;
}
MOZ_ASSERT(bytes_ >= nbytes);
bytes_ -= nbytes;
}
};
/*
* Like HeapSize, but also updates a 'parent' HeapSize. Used for per-zone heap
* size data that also updates a runtime-wide parent.
*/
class HeapSizeChild : public HeapSize {
public:
void addGCArena(HeapSize& parent) {
HeapSize::addGCArena();
parent.addGCArena();
}
void removeGCArena(HeapSize& parent) {
HeapSize::removeGCArena();
parent.removeGCArena();
}
void addBytes(size_t nbytes, HeapSize& parent) {
HeapSize::addBytes(nbytes);
parent.addBytes(nbytes);
}
void removeBytes(size_t nbytes, bool updateRetainedSize, HeapSize& parent) {
HeapSize::removeBytes(nbytes, updateRetainedSize);
parent.removeBytes(nbytes, updateRetainedSize);
}
};
class PerZoneGCHeapSize : public HeapSizeChild {
public:
size_t freedBytes() const { return freedBytes_; }
void clearFreedBytes() { freedBytes_ = 0; }
void removeGCArena(HeapSize& parent) {
HeapSizeChild::removeGCArena(parent);
freedBytes_ += ArenaSize;
}
void removeBytes(size_t nbytes, bool updateRetainedSize, HeapSize& parent) {
HeapSizeChild::removeBytes(nbytes, updateRetainedSize, parent);
freedBytes_ += nbytes;
}
private:
AtomicByteCount freedBytes_;
};
// Heap size thresholds used to trigger GC. This is an abstract base class for
// GC heap and malloc thresholds defined below.
class HeapThreshold {
protected:
HeapThreshold()
: startBytes_(SIZE_MAX),
incrementalLimitBytes_(SIZE_MAX),
sliceBytes_(SIZE_MAX) {}
// The threshold at which to start a new incremental collection.
//
// This can be read off main thread during collection, for example by sweep
// tasks that resize tables.
MainThreadOrGCTaskData<size_t> startBytes_;
// The threshold at which start a new non-incremental collection or finish an
// ongoing collection non-incrementally.
MainThreadData<size_t> incrementalLimitBytes_;
// The threshold at which to trigger a slice during an ongoing incremental
// collection.
MainThreadData<size_t> sliceBytes_;
public:
size_t startBytes() const { return startBytes_; }
size_t sliceBytes() const { return sliceBytes_; }
size_t incrementalLimitBytes() const { return incrementalLimitBytes_; }
size_t eagerAllocTrigger(bool highFrequencyGC) const;
size_t incrementalBytesRemaining(const HeapSize& heapSize) const;
void setSliceThreshold(ZoneAllocator* zone, const HeapSize& heapSize,
const GCSchedulingTunables& tunables,
bool waitingOnBGTask);
void clearSliceThreshold() { sliceBytes_ = SIZE_MAX; }
bool hasSliceThreshold() const { return sliceBytes_ != SIZE_MAX; }
protected:
static double computeZoneHeapGrowthFactorForHeapSize(
size_t lastBytes, const GCSchedulingTunables& tunables,
const GCSchedulingState& state);
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 {
public:
void updateStartThreshold(size_t lastBytes,
mozilla::Maybe<double> allocationRate,
mozilla::Maybe<double> collectionRate,
const GCSchedulingTunables& tunables,
const GCSchedulingState& state, bool isAtomsZone);
private:
// This is our original algorithm for calculating heap limits.
static size_t computeZoneTriggerBytes(double growthFactor, size_t lastBytes,
const GCSchedulingTunables& tunables);
// This is the algorithm described in the optimal heap limits paper.
static double computeBalancedHeapLimit(size_t lastBytes,
double allocationRate,
double collectionRate,
const GCSchedulingTunables& tunables);
};
// 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 {
public:
void updateStartThreshold(size_t lastBytes,
const GCSchedulingTunables& tunables,
const GCSchedulingState& state);
private:
static size_t computeZoneTriggerBytes(double growthFactor, size_t lastBytes,
size_t baseBytes);
};
// 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 {
public:
explicit JitHeapThreshold(size_t bytes) { startBytes_ = bytes; }
};
#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 {
public:
MemoryTracker();
void fixupAfterMovingGC();
void checkEmptyOnDestroy();
// 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* mem, MemoryUse use);
void unregisterNonGCMemory(void* mem, MemoryUse use);
void moveNonGCMemory(void* dst, void* src, MemoryUse use);
void incNonGCMemory(void* mem, size_t nbytes, MemoryUse use);
void decNonGCMemory(void* mem, size_t nbytes, MemoryUse use);
private:
template <typename Ptr>
struct Key {
Key(Ptr* ptr, MemoryUse use);
Ptr* ptr() const;
MemoryUse use() const;
private:
# 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 MOZ_UNANNOTATED;
// 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