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Diffstat (limited to 'src/runtime/mstats.go')
| -rw-r--r-- | src/runtime/mstats.go | 980 |
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diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go new file mode 100644 index 0000000..6defaed --- /dev/null +++ b/src/runtime/mstats.go @@ -0,0 +1,980 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Memory statistics + +package runtime + +import ( + "runtime/internal/atomic" + "unsafe" +) + +// Statistics. +// +// For detailed descriptions see the documentation for MemStats. +// Fields that differ from MemStats are further documented here. +// +// Many of these fields are updated on the fly, while others are only +// updated when updatememstats is called. +type mstats struct { + // General statistics. + alloc uint64 // bytes allocated and not yet freed + total_alloc uint64 // bytes allocated (even if freed) + sys uint64 // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate) + nlookup uint64 // number of pointer lookups (unused) + nmalloc uint64 // number of mallocs + nfree uint64 // number of frees + + // Statistics about malloc heap. + // Updated atomically, or with the world stopped. + // + // Like MemStats, heap_sys and heap_inuse do not count memory + // in manually-managed spans. + heap_sys sysMemStat // virtual address space obtained from system for GC'd heap + heap_inuse uint64 // bytes in mSpanInUse spans + heap_released uint64 // bytes released to the os + + // heap_objects is not used by the runtime directly and instead + // computed on the fly by updatememstats. + heap_objects uint64 // total number of allocated objects + + // Statistics about stacks. + stacks_inuse uint64 // bytes in manually-managed stack spans; computed by updatememstats + stacks_sys sysMemStat // only counts newosproc0 stack in mstats; differs from MemStats.StackSys + + // Statistics about allocation of low-level fixed-size structures. + // Protected by FixAlloc locks. + mspan_inuse uint64 // mspan structures + mspan_sys sysMemStat + mcache_inuse uint64 // mcache structures + mcache_sys sysMemStat + buckhash_sys sysMemStat // profiling bucket hash table + + // Statistics about GC overhead. + gcWorkBufInUse uint64 // computed by updatememstats + gcProgPtrScalarBitsInUse uint64 // computed by updatememstats + gcMiscSys sysMemStat // updated atomically or during STW + + // Miscellaneous statistics. + other_sys sysMemStat // updated atomically or during STW + + // Statistics about the garbage collector. + + // next_gc is the goal heap_live for when next GC ends. + // Set to ^uint64(0) if disabled. + // + // Read and written atomically, unless the world is stopped. + next_gc uint64 + + // Protected by mheap or stopping the world during GC. + last_gc_unix uint64 // last gc (in unix time) + pause_total_ns uint64 + pause_ns [256]uint64 // circular buffer of recent gc pause lengths + pause_end [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970) + numgc uint32 + numforcedgc uint32 // number of user-forced GCs + gc_cpu_fraction float64 // fraction of CPU time used by GC + enablegc bool + debuggc bool + + // Statistics about allocation size classes. + + by_size [_NumSizeClasses]struct { + size uint32 + nmalloc uint64 + nfree uint64 + } + + // Add an uint32 for even number of size classes to align below fields + // to 64 bits for atomic operations on 32 bit platforms. + _ [1 - _NumSizeClasses%2]uint32 + + last_gc_nanotime uint64 // last gc (monotonic time) + tinyallocs uint64 // number of tiny allocations that didn't cause actual allocation; not exported to go directly + last_next_gc uint64 // next_gc for the previous GC + last_heap_inuse uint64 // heap_inuse at mark termination of the previous GC + + // triggerRatio is the heap growth ratio that triggers marking. + // + // E.g., if this is 0.6, then GC should start when the live + // heap has reached 1.6 times the heap size marked by the + // previous cycle. This should be ≤ GOGC/100 so the trigger + // heap size is less than the goal heap size. This is set + // during mark termination for the next cycle's trigger. + triggerRatio float64 + + // gc_trigger is the heap size that triggers marking. + // + // When heap_live ≥ gc_trigger, the mark phase will start. + // This is also the heap size by which proportional sweeping + // must be complete. + // + // This is computed from triggerRatio during mark termination + // for the next cycle's trigger. + gc_trigger uint64 + + // heap_live is the number of bytes considered live by the GC. + // That is: retained by the most recent GC plus allocated + // since then. heap_live <= alloc, since alloc includes unmarked + // objects that have not yet been swept (and hence goes up as we + // allocate and down as we sweep) while heap_live excludes these + // objects (and hence only goes up between GCs). + // + // This is updated atomically without locking. To reduce + // contention, this is updated only when obtaining a span from + // an mcentral and at this point it counts all of the + // unallocated slots in that span (which will be allocated + // before that mcache obtains another span from that + // mcentral). Hence, it slightly overestimates the "true" live + // heap size. It's better to overestimate than to + // underestimate because 1) this triggers the GC earlier than + // necessary rather than potentially too late and 2) this + // leads to a conservative GC rate rather than a GC rate that + // is potentially too low. + // + // Reads should likewise be atomic (or during STW). + // + // Whenever this is updated, call traceHeapAlloc() and + // gcController.revise(). + heap_live uint64 + + // heap_scan is the number of bytes of "scannable" heap. This + // is the live heap (as counted by heap_live), but omitting + // no-scan objects and no-scan tails of objects. + // + // Whenever this is updated, call gcController.revise(). + // + // Read and written atomically or with the world stopped. + heap_scan uint64 + + // heap_marked is the number of bytes marked by the previous + // GC. After mark termination, heap_live == heap_marked, but + // unlike heap_live, heap_marked does not change until the + // next mark termination. + heap_marked uint64 + + // heapStats is a set of statistics + heapStats consistentHeapStats + + // _ uint32 // ensure gcPauseDist is aligned + + // gcPauseDist represents the distribution of all GC-related + // application pauses in the runtime. + // + // Each individual pause is counted separately, unlike pause_ns. + gcPauseDist timeHistogram +} + +var memstats mstats + +// A MemStats records statistics about the memory allocator. +type MemStats struct { + // General statistics. + + // Alloc is bytes of allocated heap objects. + // + // This is the same as HeapAlloc (see below). + Alloc uint64 + + // TotalAlloc is cumulative bytes allocated for heap objects. + // + // TotalAlloc increases as heap objects are allocated, but + // unlike Alloc and HeapAlloc, it does not decrease when + // objects are freed. + TotalAlloc uint64 + + // Sys is the total bytes of memory obtained from the OS. + // + // Sys is the sum of the XSys fields below. Sys measures the + // virtual address space reserved by the Go runtime for the + // heap, stacks, and other internal data structures. It's + // likely that not all of the virtual address space is backed + // by physical memory at any given moment, though in general + // it all was at some point. + Sys uint64 + + // Lookups is the number of pointer lookups performed by the + // runtime. + // + // This is primarily useful for debugging runtime internals. + Lookups uint64 + + // Mallocs is the cumulative count of heap objects allocated. + // The number of live objects is Mallocs - Frees. + Mallocs uint64 + + // Frees is the cumulative count of heap objects freed. + Frees uint64 + + // Heap memory statistics. + // + // Interpreting the heap statistics requires some knowledge of + // how Go organizes memory. Go divides the virtual address + // space of the heap into "spans", which are contiguous + // regions of memory 8K or larger. A span may be in one of + // three states: + // + // An "idle" span contains no objects or other data. The + // physical memory backing an idle span can be released back + // to the OS (but the virtual address space never is), or it + // can be converted into an "in use" or "stack" span. + // + // An "in use" span contains at least one heap object and may + // have free space available to allocate more heap objects. + // + // A "stack" span is used for goroutine stacks. Stack spans + // are not considered part of the heap. A span can change + // between heap and stack memory; it is never used for both + // simultaneously. + + // HeapAlloc is bytes of allocated heap objects. + // + // "Allocated" heap objects include all reachable objects, as + // well as unreachable objects that the garbage collector has + // not yet freed. Specifically, HeapAlloc increases as heap + // objects are allocated and decreases as the heap is swept + // and unreachable objects are freed. Sweeping occurs + // incrementally between GC cycles, so these two processes + // occur simultaneously, and as a result HeapAlloc tends to + // change smoothly (in contrast with the sawtooth that is + // typical of stop-the-world garbage collectors). + HeapAlloc uint64 + + // HeapSys is bytes of heap memory obtained from the OS. + // + // HeapSys measures the amount of virtual address space + // reserved for the heap. This includes virtual address space + // that has been reserved but not yet used, which consumes no + // physical memory, but tends to be small, as well as virtual + // address space for which the physical memory has been + // returned to the OS after it became unused (see HeapReleased + // for a measure of the latter). + // + // HeapSys estimates the largest size the heap has had. + HeapSys uint64 + + // HeapIdle is bytes in idle (unused) spans. + // + // Idle spans have no objects in them. These spans could be + // (and may already have been) returned to the OS, or they can + // be reused for heap allocations, or they can be reused as + // stack memory. + // + // HeapIdle minus HeapReleased estimates the amount of memory + // that could be returned to the OS, but is being retained by + // the runtime so it can grow the heap without requesting more + // memory from the OS. If this difference is significantly + // larger than the heap size, it indicates there was a recent + // transient spike in live heap size. + HeapIdle uint64 + + // HeapInuse is bytes in in-use spans. + // + // In-use spans have at least one object in them. These spans + // can only be used for other objects of roughly the same + // size. + // + // HeapInuse minus HeapAlloc estimates the amount of memory + // that has been dedicated to particular size classes, but is + // not currently being used. This is an upper bound on + // fragmentation, but in general this memory can be reused + // efficiently. + HeapInuse uint64 + + // HeapReleased is bytes of physical memory returned to the OS. + // + // This counts heap memory from idle spans that was returned + // to the OS and has not yet been reacquired for the heap. + HeapReleased uint64 + + // HeapObjects is the number of allocated heap objects. + // + // Like HeapAlloc, this increases as objects are allocated and + // decreases as the heap is swept and unreachable objects are + // freed. + HeapObjects uint64 + + // Stack memory statistics. + // + // Stacks are not considered part of the heap, but the runtime + // can reuse a span of heap memory for stack memory, and + // vice-versa. + + // StackInuse is bytes in stack spans. + // + // In-use stack spans have at least one stack in them. These + // spans can only be used for other stacks of the same size. + // + // There is no StackIdle because unused stack spans are + // returned to the heap (and hence counted toward HeapIdle). + StackInuse uint64 + + // StackSys is bytes of stack memory obtained from the OS. + // + // StackSys is StackInuse, plus any memory obtained directly + // from the OS for OS thread stacks (which should be minimal). + StackSys uint64 + + // Off-heap memory statistics. + // + // The following statistics measure runtime-internal + // structures that are not allocated from heap memory (usually + // because they are part of implementing the heap). Unlike + // heap or stack memory, any memory allocated to these + // structures is dedicated to these structures. + // + // These are primarily useful for debugging runtime memory + // overheads. + + // MSpanInuse is bytes of allocated mspan structures. + MSpanInuse uint64 + + // MSpanSys is bytes of memory obtained from the OS for mspan + // structures. + MSpanSys uint64 + + // MCacheInuse is bytes of allocated mcache structures. + MCacheInuse uint64 + + // MCacheSys is bytes of memory obtained from the OS for + // mcache structures. + MCacheSys uint64 + + // BuckHashSys is bytes of memory in profiling bucket hash tables. + BuckHashSys uint64 + + // GCSys is bytes of memory in garbage collection metadata. + GCSys uint64 + + // OtherSys is bytes of memory in miscellaneous off-heap + // runtime allocations. + OtherSys uint64 + + // Garbage collector statistics. + + // NextGC is the target heap size of the next GC cycle. + // + // The garbage collector's goal is to keep HeapAlloc ≤ NextGC. + // At the end of each GC cycle, the target for the next cycle + // is computed based on the amount of reachable data and the + // value of GOGC. + NextGC uint64 + + // LastGC is the time the last garbage collection finished, as + // nanoseconds since 1970 (the UNIX epoch). + LastGC uint64 + + // PauseTotalNs is the cumulative nanoseconds in GC + // stop-the-world pauses since the program started. + // + // During a stop-the-world pause, all goroutines are paused + // and only the garbage collector can run. + PauseTotalNs uint64 + + // PauseNs is a circular buffer of recent GC stop-the-world + // pause times in nanoseconds. + // + // The most recent pause is at PauseNs[(NumGC+255)%256]. In + // general, PauseNs[N%256] records the time paused in the most + // recent N%256th GC cycle. There may be multiple pauses per + // GC cycle; this is the sum of all pauses during a cycle. + PauseNs [256]uint64 + + // PauseEnd is a circular buffer of recent GC pause end times, + // as nanoseconds since 1970 (the UNIX epoch). + // + // This buffer is filled the same way as PauseNs. There may be + // multiple pauses per GC cycle; this records the end of the + // last pause in a cycle. + PauseEnd [256]uint64 + + // NumGC is the number of completed GC cycles. + NumGC uint32 + + // NumForcedGC is the number of GC cycles that were forced by + // the application calling the GC function. + NumForcedGC uint32 + + // GCCPUFraction is the fraction of this program's available + // CPU time used by the GC since the program started. + // + // GCCPUFraction is expressed as a number between 0 and 1, + // where 0 means GC has consumed none of this program's CPU. A + // program's available CPU time is defined as the integral of + // GOMAXPROCS since the program started. That is, if + // GOMAXPROCS is 2 and a program has been running for 10 + // seconds, its "available CPU" is 20 seconds. GCCPUFraction + // does not include CPU time used for write barrier activity. + // + // This is the same as the fraction of CPU reported by + // GODEBUG=gctrace=1. + GCCPUFraction float64 + + // EnableGC indicates that GC is enabled. It is always true, + // even if GOGC=off. + EnableGC bool + + // DebugGC is currently unused. + DebugGC bool + + // BySize reports per-size class allocation statistics. + // + // BySize[N] gives statistics for allocations of size S where + // BySize[N-1].Size < S ≤ BySize[N].Size. + // + // This does not report allocations larger than BySize[60].Size. + BySize [61]struct { + // Size is the maximum byte size of an object in this + // size class. + Size uint32 + + // Mallocs is the cumulative count of heap objects + // allocated in this size class. The cumulative bytes + // of allocation is Size*Mallocs. The number of live + // objects in this size class is Mallocs - Frees. + Mallocs uint64 + + // Frees is the cumulative count of heap objects freed + // in this size class. + Frees uint64 + } +} + +func init() { + if offset := unsafe.Offsetof(memstats.heap_live); offset%8 != 0 { + println(offset) + throw("memstats.heap_live not aligned to 8 bytes") + } + if offset := unsafe.Offsetof(memstats.heapStats); offset%8 != 0 { + println(offset) + throw("memstats.heapStats not aligned to 8 bytes") + } + if offset := unsafe.Offsetof(memstats.gcPauseDist); offset%8 != 0 { + println(offset) + throw("memstats.gcPauseDist not aligned to 8 bytes") + } + // Ensure the size of heapStatsDelta causes adjacent fields/slots (e.g. + // [3]heapStatsDelta) to be 8-byte aligned. + if size := unsafe.Sizeof(heapStatsDelta{}); size%8 != 0 { + println(size) + throw("heapStatsDelta not a multiple of 8 bytes in size") + } +} + +// ReadMemStats populates m with memory allocator statistics. +// +// The returned memory allocator statistics are up to date as of the +// call to ReadMemStats. This is in contrast with a heap profile, +// which is a snapshot as of the most recently completed garbage +// collection cycle. +func ReadMemStats(m *MemStats) { + stopTheWorld("read mem stats") + + systemstack(func() { + readmemstats_m(m) + }) + + startTheWorld() +} + +func readmemstats_m(stats *MemStats) { + updatememstats() + + stats.Alloc = memstats.alloc + stats.TotalAlloc = memstats.total_alloc + stats.Sys = memstats.sys + stats.Mallocs = memstats.nmalloc + stats.Frees = memstats.nfree + stats.HeapAlloc = memstats.alloc + stats.HeapSys = memstats.heap_sys.load() + // By definition, HeapIdle is memory that was mapped + // for the heap but is not currently used to hold heap + // objects. It also specifically is memory that can be + // used for other purposes, like stacks, but this memory + // is subtracted out of HeapSys before it makes that + // transition. Put another way: + // + // heap_sys = bytes allocated from the OS for the heap - bytes ultimately used for non-heap purposes + // heap_idle = bytes allocated from the OS for the heap - bytes ultimately used for any purpose + // + // or + // + // heap_sys = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse + // heap_idle = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse - heap_inuse + // + // => heap_idle = heap_sys - heap_inuse + stats.HeapIdle = memstats.heap_sys.load() - memstats.heap_inuse + stats.HeapInuse = memstats.heap_inuse + stats.HeapReleased = memstats.heap_released + stats.HeapObjects = memstats.heap_objects + stats.StackInuse = memstats.stacks_inuse + // memstats.stacks_sys is only memory mapped directly for OS stacks. + // Add in heap-allocated stack memory for user consumption. + stats.StackSys = memstats.stacks_inuse + memstats.stacks_sys.load() + stats.MSpanInuse = memstats.mspan_inuse + stats.MSpanSys = memstats.mspan_sys.load() + stats.MCacheInuse = memstats.mcache_inuse + stats.MCacheSys = memstats.mcache_sys.load() + stats.BuckHashSys = memstats.buckhash_sys.load() + // MemStats defines GCSys as an aggregate of all memory related + // to the memory management system, but we track this memory + // at a more granular level in the runtime. + stats.GCSys = memstats.gcMiscSys.load() + memstats.gcWorkBufInUse + memstats.gcProgPtrScalarBitsInUse + stats.OtherSys = memstats.other_sys.load() + stats.NextGC = memstats.next_gc + stats.LastGC = memstats.last_gc_unix + stats.PauseTotalNs = memstats.pause_total_ns + stats.PauseNs = memstats.pause_ns + stats.PauseEnd = memstats.pause_end + stats.NumGC = memstats.numgc + stats.NumForcedGC = memstats.numforcedgc + stats.GCCPUFraction = memstats.gc_cpu_fraction + stats.EnableGC = true + + // Handle BySize. Copy N values, where N is + // the minimum of the lengths of the two arrays. + // Unfortunately copy() won't work here because + // the arrays have different structs. + // + // TODO(mknyszek): Consider renaming the fields + // of by_size's elements to align so we can use + // the copy built-in. + bySizeLen := len(stats.BySize) + if l := len(memstats.by_size); l < bySizeLen { + bySizeLen = l + } + for i := 0; i < bySizeLen; i++ { + stats.BySize[i].Size = memstats.by_size[i].size + stats.BySize[i].Mallocs = memstats.by_size[i].nmalloc + stats.BySize[i].Frees = memstats.by_size[i].nfree + } +} + +//go:linkname readGCStats runtime/debug.readGCStats +func readGCStats(pauses *[]uint64) { + systemstack(func() { + readGCStats_m(pauses) + }) +} + +// readGCStats_m must be called on the system stack because it acquires the heap +// lock. See mheap for details. +//go:systemstack +func readGCStats_m(pauses *[]uint64) { + p := *pauses + // Calling code in runtime/debug should make the slice large enough. + if cap(p) < len(memstats.pause_ns)+3 { + throw("short slice passed to readGCStats") + } + + // Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns. + lock(&mheap_.lock) + + n := memstats.numgc + if n > uint32(len(memstats.pause_ns)) { + n = uint32(len(memstats.pause_ns)) + } + + // The pause buffer is circular. The most recent pause is at + // pause_ns[(numgc-1)%len(pause_ns)], and then backward + // from there to go back farther in time. We deliver the times + // most recent first (in p[0]). + p = p[:cap(p)] + for i := uint32(0); i < n; i++ { + j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns)) + p[i] = memstats.pause_ns[j] + p[n+i] = memstats.pause_end[j] + } + + p[n+n] = memstats.last_gc_unix + p[n+n+1] = uint64(memstats.numgc) + p[n+n+2] = memstats.pause_total_ns + unlock(&mheap_.lock) + *pauses = p[:n+n+3] +} + +// Updates the memstats structure. +// +// The world must be stopped. +// +//go:nowritebarrier +func updatememstats() { + assertWorldStopped() + + // Flush mcaches to mcentral before doing anything else. + // + // Flushing to the mcentral may in general cause stats to + // change as mcentral data structures are manipulated. + systemstack(flushallmcaches) + + memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse) + memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse) + memstats.sys = memstats.heap_sys.load() + memstats.stacks_sys.load() + memstats.mspan_sys.load() + + memstats.mcache_sys.load() + memstats.buckhash_sys.load() + memstats.gcMiscSys.load() + + memstats.other_sys.load() + + // Calculate memory allocator stats. + // During program execution we only count number of frees and amount of freed memory. + // Current number of alive objects in the heap and amount of alive heap memory + // are calculated by scanning all spans. + // Total number of mallocs is calculated as number of frees plus number of alive objects. + // Similarly, total amount of allocated memory is calculated as amount of freed memory + // plus amount of alive heap memory. + memstats.alloc = 0 + memstats.total_alloc = 0 + memstats.nmalloc = 0 + memstats.nfree = 0 + for i := 0; i < len(memstats.by_size); i++ { + memstats.by_size[i].nmalloc = 0 + memstats.by_size[i].nfree = 0 + } + // Collect consistent stats, which are the source-of-truth in the some cases. + var consStats heapStatsDelta + memstats.heapStats.unsafeRead(&consStats) + + // Collect large allocation stats. + totalAlloc := uint64(consStats.largeAlloc) + memstats.nmalloc += uint64(consStats.largeAllocCount) + totalFree := uint64(consStats.largeFree) + memstats.nfree += uint64(consStats.largeFreeCount) + + // Collect per-sizeclass stats. + for i := 0; i < _NumSizeClasses; i++ { + // Malloc stats. + a := uint64(consStats.smallAllocCount[i]) + totalAlloc += a * uint64(class_to_size[i]) + memstats.nmalloc += a + memstats.by_size[i].nmalloc = a + + // Free stats. + f := uint64(consStats.smallFreeCount[i]) + totalFree += f * uint64(class_to_size[i]) + memstats.nfree += f + memstats.by_size[i].nfree = f + } + + // Account for tiny allocations. + memstats.nfree += memstats.tinyallocs + memstats.nmalloc += memstats.tinyallocs + + // Calculate derived stats. + memstats.total_alloc = totalAlloc + memstats.alloc = totalAlloc - totalFree + memstats.heap_objects = memstats.nmalloc - memstats.nfree + + memstats.stacks_inuse = uint64(consStats.inStacks) + memstats.gcWorkBufInUse = uint64(consStats.inWorkBufs) + memstats.gcProgPtrScalarBitsInUse = uint64(consStats.inPtrScalarBits) + + // We also count stacks_inuse, gcWorkBufInUse, and gcProgPtrScalarBitsInUse as sys memory. + memstats.sys += memstats.stacks_inuse + memstats.gcWorkBufInUse + memstats.gcProgPtrScalarBitsInUse + + // The world is stopped, so the consistent stats (after aggregation) + // should be identical to some combination of memstats. In particular: + // + // * heap_inuse == inHeap + // * heap_released == released + // * heap_sys - heap_released == committed - inStacks - inWorkBufs - inPtrScalarBits + // + // Check if that's actually true. + // + // TODO(mknyszek): Maybe don't throw here. It would be bad if a + // bug in otherwise benign accounting caused the whole application + // to crash. + if memstats.heap_inuse != uint64(consStats.inHeap) { + print("runtime: heap_inuse=", memstats.heap_inuse, "\n") + print("runtime: consistent value=", consStats.inHeap, "\n") + throw("heap_inuse and consistent stats are not equal") + } + if memstats.heap_released != uint64(consStats.released) { + print("runtime: heap_released=", memstats.heap_released, "\n") + print("runtime: consistent value=", consStats.released, "\n") + throw("heap_released and consistent stats are not equal") + } + globalRetained := memstats.heap_sys.load() - memstats.heap_released + consRetained := uint64(consStats.committed - consStats.inStacks - consStats.inWorkBufs - consStats.inPtrScalarBits) + if globalRetained != consRetained { + print("runtime: global value=", globalRetained, "\n") + print("runtime: consistent value=", consRetained, "\n") + throw("measures of the retained heap are not equal") + } +} + +// flushmcache flushes the mcache of allp[i]. +// +// The world must be stopped. +// +//go:nowritebarrier +func flushmcache(i int) { + assertWorldStopped() + + p := allp[i] + c := p.mcache + if c == nil { + return + } + c.releaseAll() + stackcache_clear(c) +} + +// flushallmcaches flushes the mcaches of all Ps. +// +// The world must be stopped. +// +//go:nowritebarrier +func flushallmcaches() { + assertWorldStopped() + + for i := 0; i < int(gomaxprocs); i++ { + flushmcache(i) + } +} + +// sysMemStat represents a global system statistic that is managed atomically. +// +// This type must structurally be a uint64 so that mstats aligns with MemStats. +type sysMemStat uint64 + +// load atomically reads the value of the stat. +// +// Must be nosplit as it is called in runtime initialization, e.g. newosproc0. +//go:nosplit +func (s *sysMemStat) load() uint64 { + return atomic.Load64((*uint64)(s)) +} + +// add atomically adds the sysMemStat by n. +// +// Must be nosplit as it is called in runtime initialization, e.g. newosproc0. +//go:nosplit +func (s *sysMemStat) add(n int64) { + if s == nil { + return + } + val := atomic.Xadd64((*uint64)(s), n) + if (n > 0 && int64(val) < n) || (n < 0 && int64(val)+n < n) { + print("runtime: val=", val, " n=", n, "\n") + throw("sysMemStat overflow") + } +} + +// heapStatsDelta contains deltas of various runtime memory statistics +// that need to be updated together in order for them to be kept +// consistent with one another. +type heapStatsDelta struct { + // Memory stats. + committed int64 // byte delta of memory committed + released int64 // byte delta of released memory generated + inHeap int64 // byte delta of memory placed in the heap + inStacks int64 // byte delta of memory reserved for stacks + inWorkBufs int64 // byte delta of memory reserved for work bufs + inPtrScalarBits int64 // byte delta of memory reserved for unrolled GC prog bits + + // Allocator stats. + largeAlloc uintptr // bytes allocated for large objects + largeAllocCount uintptr // number of large object allocations + smallAllocCount [_NumSizeClasses]uintptr // number of allocs for small objects + largeFree uintptr // bytes freed for large objects (>maxSmallSize) + largeFreeCount uintptr // number of frees for large objects (>maxSmallSize) + smallFreeCount [_NumSizeClasses]uintptr // number of frees for small objects (<=maxSmallSize) + + // Add a uint32 to ensure this struct is a multiple of 8 bytes in size. + // Only necessary on 32-bit platforms. + // _ [(sys.PtrSize / 4) % 2]uint32 +} + +// merge adds in the deltas from b into a. +func (a *heapStatsDelta) merge(b *heapStatsDelta) { + a.committed += b.committed + a.released += b.released + a.inHeap += b.inHeap + a.inStacks += b.inStacks + a.inWorkBufs += b.inWorkBufs + a.inPtrScalarBits += b.inPtrScalarBits + + a.largeAlloc += b.largeAlloc + a.largeAllocCount += b.largeAllocCount + for i := range b.smallAllocCount { + a.smallAllocCount[i] += b.smallAllocCount[i] + } + a.largeFree += b.largeFree + a.largeFreeCount += b.largeFreeCount + for i := range b.smallFreeCount { + a.smallFreeCount[i] += b.smallFreeCount[i] + } +} + +// consistentHeapStats represents a set of various memory statistics +// whose updates must be viewed completely to get a consistent +// state of the world. +// +// To write updates to memory stats use the acquire and release +// methods. To obtain a consistent global snapshot of these statistics, +// use read. +type consistentHeapStats struct { + // stats is a ring buffer of heapStatsDelta values. + // Writers always atomically update the delta at index gen. + // + // Readers operate by rotating gen (0 -> 1 -> 2 -> 0 -> ...) + // and synchronizing with writers by observing each P's + // statsSeq field. If the reader observes a P not writing, + // it can be sure that it will pick up the new gen value the + // next time it writes. + // + // The reader then takes responsibility by clearing space + // in the ring buffer for the next reader to rotate gen to + // that space (i.e. it merges in values from index (gen-2) mod 3 + // to index (gen-1) mod 3, then clears the former). + // + // Note that this means only one reader can be reading at a time. + // There is no way for readers to synchronize. + // + // This process is why we need a ring buffer of size 3 instead + // of 2: one is for the writers, one contains the most recent + // data, and the last one is clear so writers can begin writing + // to it the moment gen is updated. + stats [3]heapStatsDelta + + // gen represents the current index into which writers + // are writing, and can take on the value of 0, 1, or 2. + // This value is updated atomically. + gen uint32 + + // noPLock is intended to provide mutual exclusion for updating + // stats when no P is available. It does not block other writers + // with a P, only other writers without a P and the reader. Because + // stats are usually updated when a P is available, contention on + // this lock should be minimal. + noPLock mutex +} + +// acquire returns a heapStatsDelta to be updated. In effect, +// it acquires the shard for writing. release must be called +// as soon as the relevant deltas are updated. +// +// The returned heapStatsDelta must be updated atomically. +// +// The caller's P must not change between acquire and +// release. This also means that the caller should not +// acquire a P or release its P in between. +func (m *consistentHeapStats) acquire() *heapStatsDelta { + if pp := getg().m.p.ptr(); pp != nil { + seq := atomic.Xadd(&pp.statsSeq, 1) + if seq%2 == 0 { + // Should have been incremented to odd. + print("runtime: seq=", seq, "\n") + throw("bad sequence number") + } + } else { + lock(&m.noPLock) + } + gen := atomic.Load(&m.gen) % 3 + return &m.stats[gen] +} + +// release indicates that the writer is done modifying +// the delta. The value returned by the corresponding +// acquire must no longer be accessed or modified after +// release is called. +// +// The caller's P must not change between acquire and +// release. This also means that the caller should not +// acquire a P or release its P in between. +func (m *consistentHeapStats) release() { + if pp := getg().m.p.ptr(); pp != nil { + seq := atomic.Xadd(&pp.statsSeq, 1) + if seq%2 != 0 { + // Should have been incremented to even. + print("runtime: seq=", seq, "\n") + throw("bad sequence number") + } + } else { + unlock(&m.noPLock) + } +} + +// unsafeRead aggregates the delta for this shard into out. +// +// Unsafe because it does so without any synchronization. The +// world must be stopped. +func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) { + assertWorldStopped() + + for i := range m.stats { + out.merge(&m.stats[i]) + } +} + +// unsafeClear clears the shard. +// +// Unsafe because the world must be stopped and values should +// be donated elsewhere before clearing. +func (m *consistentHeapStats) unsafeClear() { + assertWorldStopped() + + for i := range m.stats { + m.stats[i] = heapStatsDelta{} + } +} + +// read takes a globally consistent snapshot of m +// and puts the aggregated value in out. Even though out is a +// heapStatsDelta, the resulting values should be complete and +// valid statistic values. +// +// Not safe to call concurrently. The world must be stopped +// or metricsSema must be held. +func (m *consistentHeapStats) read(out *heapStatsDelta) { + // Getting preempted after this point is not safe because + // we read allp. We need to make sure a STW can't happen + // so it doesn't change out from under us. + mp := acquirem() + + // Get the current generation. We can be confident that this + // will not change since read is serialized and is the only + // one that modifies currGen. + currGen := atomic.Load(&m.gen) + prevGen := currGen - 1 + if currGen == 0 { + prevGen = 2 + } + + // Prevent writers without a P from writing while we update gen. + lock(&m.noPLock) + + // Rotate gen, effectively taking a snapshot of the state of + // these statistics at the point of the exchange by moving + // writers to the next set of deltas. + // + // This exchange is safe to do because we won't race + // with anyone else trying to update this value. + atomic.Xchg(&m.gen, (currGen+1)%3) + + // Allow P-less writers to continue. They'll be writing to the + // next generation now. + unlock(&m.noPLock) + + for _, p := range allp { + // Spin until there are no more writers. + for atomic.Load(&p.statsSeq)%2 != 0 { + } + } + + // At this point we've observed that each sequence + // number is even, so any future writers will observe + // the new gen value. That means it's safe to read from + // the other deltas in the stats buffer. + + // Perform our responsibilities and free up + // stats[prevGen] for the next time we want to take + // a snapshot. + m.stats[currGen].merge(&m.stats[prevGen]) + m.stats[prevGen] = heapStatsDelta{} + + // Finally, copy out the complete delta. + *out = m.stats[currGen] + + releasem(mp) +} |