/* -*- 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 http://mozilla.org/MPL/2.0/. */ /* * [SMDOC] GC Scheduling * * GC Scheduling Overview * ====================== * * See also GC scheduling from Firefox's perspective here: * https://searchfox.org/mozilla-central/source/dom/base/CCGCScheduler.cpp * * 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_FREE_THRESHOLD_FOR_IDLE_COLLECTION \ * JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION_FRACTION \ * JSGC_NURSERY_TIMEOUT_FOR_IDLE_COLLECTION_MS \ * \ * Attempt to run a minor GC in the idle time if the free space falls below \ * this threshold or if it hasn't been collected for too long. The absolute \ * threshold is used when the nursery is large and the percentage when it is \ * small. See Nursery::shouldCollect(). \ */ \ _(JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION, size_t, \ nurseryFreeThresholdForIdleCollection, ConvertSize, NoCheck, \ ChunkSize / 4) \ _(JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION_PERCENT, double, \ nurseryFreeThresholdForIdleCollectionFraction, ConvertTimes100, \ CheckNonZeroUnitRange, 0.25) \ _(JSGC_NURSERY_TIMEOUT_FOR_IDLE_COLLECTION_MS, mozilla::TimeDuration, \ nurseryTimeoutForIdleCollection, 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_PRETENURE_THRESHOLD \ * \ * 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. \ */ \ _(JSGC_PRETENURE_THRESHOLD, double, pretenureThreshold, ConvertTimes100, \ CheckNonZeroUnitRange, 0.6) \ \ /* \ * JSGC_PRETENURE_STRING_THRESHOLD \ * \ * If the percentage of the tenured strings exceeds this threshold, string \ * will be allocated in tenured heap instead. (Default is allocated in \ * nursery.) \ */ \ _(JSGC_PRETENURE_STRING_THRESHOLD, double, pretenureStringThreshold, \ ConvertTimes100, CheckNonZeroUnitRange, 0.55) \ \ /* \ * JSGC_STOP_PRETENURE_STRING_THRESHOLD \ * \ * If the finalization rate of the tenured strings exceeds this threshold, \ * string will be allocated in nursery. \ */ \ _(JSGC_STOP_PRETENURE_STRING_THRESHOLD, double, \ stopPretenureStringThreshold, ConvertTimes100, CheckNonZeroUnitRange, 0.9) \ \ /* \ * 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_KB \ */ \ _(JSGC_PARALLEL_MARKING_THRESHOLD_KB, size_t, parallelMarkingThresholdBytes, \ ConvertKB, NoCheck, 10 * 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_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 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 bool attemptPretenuring() const { return pretenureThreshold_ < 1.0; } 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 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; /* * 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 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 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 startBytes_; // The threshold at which start a new non-incremental collection or finish an // ongoing collection non-incrementally. MainThreadData incrementalLimitBytes_; // The threshold at which to trigger a slice during an ongoing incremental // collection. MainThreadData sliceBytes_; public: size_t startBytes() const { return startBytes_; } size_t sliceBytes() const { return sliceBytes_; } size_t incrementalLimitBytes() const { return incrementalLimitBytes_; } double 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 allocationRate, mozilla::Maybe 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* 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); private: template 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 struct Hasher { using KeyT = Key; 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 using Map = HashMap, size_t, Hasher, SystemAllocPolicy>; using GCMap = Map; using NonGCMap = Map; static bool isGCMemoryUse(MemoryUse use); static bool isNonGCMemoryUse(MemoryUse use); static bool allowMultipleAssociations(MemoryUse use); size_t getAndRemoveEntry(const Key& key, LockGuard& 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