| // 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. |
| |
| // Page heap. |
| // |
| // See malloc.go for overview. |
| |
| package runtime |
| |
| import ( |
| "internal/cpu" |
| "runtime/internal/atomic" |
| "runtime/internal/sys" |
| "unsafe" |
| ) |
| |
| // minPhysPageSize is a lower-bound on the physical page size. The |
| // true physical page size may be larger than this. In contrast, |
| // sys.PhysPageSize is an upper-bound on the physical page size. |
| const minPhysPageSize = 4096 |
| |
| // Main malloc heap. |
| // The heap itself is the "free" and "scav" treaps, |
| // but all the other global data is here too. |
| // |
| // mheap must not be heap-allocated because it contains mSpanLists, |
| // which must not be heap-allocated. |
| // |
| //go:notinheap |
| type mheap struct { |
| lock mutex |
| free mTreap // free and non-scavenged spans |
| scav mTreap // free and scavenged spans |
| sweepgen uint32 // sweep generation, see comment in mspan |
| sweepdone uint32 // all spans are swept |
| sweepers uint32 // number of active sweepone calls |
| |
| // allspans is a slice of all mspans ever created. Each mspan |
| // appears exactly once. |
| // |
| // The memory for allspans is manually managed and can be |
| // reallocated and move as the heap grows. |
| // |
| // In general, allspans is protected by mheap_.lock, which |
| // prevents concurrent access as well as freeing the backing |
| // store. Accesses during STW might not hold the lock, but |
| // must ensure that allocation cannot happen around the |
| // access (since that may free the backing store). |
| allspans []*mspan // all spans out there |
| |
| // sweepSpans contains two mspan stacks: one of swept in-use |
| // spans, and one of unswept in-use spans. These two trade |
| // roles on each GC cycle. Since the sweepgen increases by 2 |
| // on each cycle, this means the swept spans are in |
| // sweepSpans[sweepgen/2%2] and the unswept spans are in |
| // sweepSpans[1-sweepgen/2%2]. Sweeping pops spans from the |
| // unswept stack and pushes spans that are still in-use on the |
| // swept stack. Likewise, allocating an in-use span pushes it |
| // on the swept stack. |
| sweepSpans [2]gcSweepBuf |
| |
| _ uint32 // align uint64 fields on 32-bit for atomics |
| |
| // Proportional sweep |
| // |
| // These parameters represent a linear function from heap_live |
| // to page sweep count. The proportional sweep system works to |
| // stay in the black by keeping the current page sweep count |
| // above this line at the current heap_live. |
| // |
| // The line has slope sweepPagesPerByte and passes through a |
| // basis point at (sweepHeapLiveBasis, pagesSweptBasis). At |
| // any given time, the system is at (memstats.heap_live, |
| // pagesSwept) in this space. |
| // |
| // It's important that the line pass through a point we |
| // control rather than simply starting at a (0,0) origin |
| // because that lets us adjust sweep pacing at any time while |
| // accounting for current progress. If we could only adjust |
| // the slope, it would create a discontinuity in debt if any |
| // progress has already been made. |
| pagesInUse uint64 // pages of spans in stats mSpanInUse; R/W with mheap.lock |
| pagesSwept uint64 // pages swept this cycle; updated atomically |
| pagesSweptBasis uint64 // pagesSwept to use as the origin of the sweep ratio; updated atomically |
| sweepHeapLiveBasis uint64 // value of heap_live to use as the origin of sweep ratio; written with lock, read without |
| sweepPagesPerByte float64 // proportional sweep ratio; written with lock, read without |
| // TODO(austin): pagesInUse should be a uintptr, but the 386 |
| // compiler can't 8-byte align fields. |
| |
| // Page reclaimer state |
| |
| // reclaimIndex is the page index in allArenas of next page to |
| // reclaim. Specifically, it refers to page (i % |
| // pagesPerArena) of arena allArenas[i / pagesPerArena]. |
| // |
| // If this is >= 1<<63, the page reclaimer is done scanning |
| // the page marks. |
| // |
| // This is accessed atomically. |
| reclaimIndex uint64 |
| // reclaimCredit is spare credit for extra pages swept. Since |
| // the page reclaimer works in large chunks, it may reclaim |
| // more than requested. Any spare pages released go to this |
| // credit pool. |
| // |
| // This is accessed atomically. |
| reclaimCredit uintptr |
| |
| // scavengeCredit is spare credit for extra bytes scavenged. |
| // Since the scavenging mechanisms operate on spans, it may |
| // scavenge more than requested. Any spare pages released |
| // go to this credit pool. |
| // |
| // This is protected by the mheap lock. |
| scavengeCredit uintptr |
| |
| // Malloc stats. |
| largealloc uint64 // bytes allocated for large objects |
| nlargealloc uint64 // number of large object allocations |
| largefree uint64 // bytes freed for large objects (>maxsmallsize) |
| nlargefree uint64 // number of frees for large objects (>maxsmallsize) |
| nsmallfree [_NumSizeClasses]uint64 // number of frees for small objects (<=maxsmallsize) |
| |
| // arenas is the heap arena map. It points to the metadata for |
| // the heap for every arena frame of the entire usable virtual |
| // address space. |
| // |
| // Use arenaIndex to compute indexes into this array. |
| // |
| // For regions of the address space that are not backed by the |
| // Go heap, the arena map contains nil. |
| // |
| // Modifications are protected by mheap_.lock. Reads can be |
| // performed without locking; however, a given entry can |
| // transition from nil to non-nil at any time when the lock |
| // isn't held. (Entries never transitions back to nil.) |
| // |
| // In general, this is a two-level mapping consisting of an L1 |
| // map and possibly many L2 maps. This saves space when there |
| // are a huge number of arena frames. However, on many |
| // platforms (even 64-bit), arenaL1Bits is 0, making this |
| // effectively a single-level map. In this case, arenas[0] |
| // will never be nil. |
| arenas [1 << arenaL1Bits]*[1 << arenaL2Bits]*heapArena |
| |
| // heapArenaAlloc is pre-reserved space for allocating heapArena |
| // objects. This is only used on 32-bit, where we pre-reserve |
| // this space to avoid interleaving it with the heap itself. |
| heapArenaAlloc linearAlloc |
| |
| // arenaHints is a list of addresses at which to attempt to |
| // add more heap arenas. This is initially populated with a |
| // set of general hint addresses, and grown with the bounds of |
| // actual heap arena ranges. |
| arenaHints *arenaHint |
| |
| // arena is a pre-reserved space for allocating heap arenas |
| // (the actual arenas). This is only used on 32-bit. |
| arena linearAlloc |
| |
| // allArenas is the arenaIndex of every mapped arena. This can |
| // be used to iterate through the address space. |
| // |
| // Access is protected by mheap_.lock. However, since this is |
| // append-only and old backing arrays are never freed, it is |
| // safe to acquire mheap_.lock, copy the slice header, and |
| // then release mheap_.lock. |
| allArenas []arenaIdx |
| |
| // sweepArenas is a snapshot of allArenas taken at the |
| // beginning of the sweep cycle. This can be read safely by |
| // simply blocking GC (by disabling preemption). |
| sweepArenas []arenaIdx |
| |
| // _ uint32 // ensure 64-bit alignment of central |
| |
| // central free lists for small size classes. |
| // the padding makes sure that the mcentrals are |
| // spaced CacheLinePadSize bytes apart, so that each mcentral.lock |
| // gets its own cache line. |
| // central is indexed by spanClass. |
| central [numSpanClasses]struct { |
| mcentral mcentral |
| pad [cpu.CacheLinePadSize - unsafe.Sizeof(mcentral{})%cpu.CacheLinePadSize]byte |
| } |
| |
| spanalloc fixalloc // allocator for span* |
| cachealloc fixalloc // allocator for mcache* |
| treapalloc fixalloc // allocator for treapNodes* |
| specialfinalizeralloc fixalloc // allocator for specialfinalizer* |
| specialprofilealloc fixalloc // allocator for specialprofile* |
| speciallock mutex // lock for special record allocators. |
| arenaHintAlloc fixalloc // allocator for arenaHints |
| |
| unused *specialfinalizer // never set, just here to force the specialfinalizer type into DWARF |
| } |
| |
| var mheap_ mheap |
| |
| // A heapArena stores metadata for a heap arena. heapArenas are stored |
| // outside of the Go heap and accessed via the mheap_.arenas index. |
| // |
| // This gets allocated directly from the OS, so ideally it should be a |
| // multiple of the system page size. For example, avoid adding small |
| // fields. |
| // |
| //go:notinheap |
| type heapArena struct { |
| // bitmap stores the pointer/scalar bitmap for the words in |
| // this arena. See mbitmap.go for a description. Use the |
| // heapBits type to access this. |
| bitmap [heapArenaBitmapBytes]byte |
| |
| // spans maps from virtual address page ID within this arena to *mspan. |
| // For allocated spans, their pages map to the span itself. |
| // For free spans, only the lowest and highest pages map to the span itself. |
| // Internal pages map to an arbitrary span. |
| // For pages that have never been allocated, spans entries are nil. |
| // |
| // Modifications are protected by mheap.lock. Reads can be |
| // performed without locking, but ONLY from indexes that are |
| // known to contain in-use or stack spans. This means there |
| // must not be a safe-point between establishing that an |
| // address is live and looking it up in the spans array. |
| spans [pagesPerArena]*mspan |
| |
| // pageInUse is a bitmap that indicates which spans are in |
| // state mSpanInUse. This bitmap is indexed by page number, |
| // but only the bit corresponding to the first page in each |
| // span is used. |
| // |
| // Writes are protected by mheap_.lock. |
| pageInUse [pagesPerArena / 8]uint8 |
| |
| // pageMarks is a bitmap that indicates which spans have any |
| // marked objects on them. Like pageInUse, only the bit |
| // corresponding to the first page in each span is used. |
| // |
| // Writes are done atomically during marking. Reads are |
| // non-atomic and lock-free since they only occur during |
| // sweeping (and hence never race with writes). |
| // |
| // This is used to quickly find whole spans that can be freed. |
| // |
| // TODO(austin): It would be nice if this was uint64 for |
| // faster scanning, but we don't have 64-bit atomic bit |
| // operations. |
| pageMarks [pagesPerArena / 8]uint8 |
| } |
| |
| // arenaHint is a hint for where to grow the heap arenas. See |
| // mheap_.arenaHints. |
| // |
| //go:notinheap |
| type arenaHint struct { |
| addr uintptr |
| down bool |
| next *arenaHint |
| } |
| |
| // An mspan is a run of pages. |
| // |
| // When a mspan is in the heap free treap, state == mSpanFree |
| // and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span. |
| // If the mspan is in the heap scav treap, then in addition to the |
| // above scavenged == true. scavenged == false in all other cases. |
| // |
| // When a mspan is allocated, state == mSpanInUse or mSpanManual |
| // and heapmap(i) == span for all s->start <= i < s->start+s->npages. |
| |
| // Every mspan is in one doubly-linked list, either in the mheap's |
| // busy list or one of the mcentral's span lists. |
| |
| // An mspan representing actual memory has state mSpanInUse, |
| // mSpanManual, or mSpanFree. Transitions between these states are |
| // constrained as follows: |
| // |
| // * A span may transition from free to in-use or manual during any GC |
| // phase. |
| // |
| // * During sweeping (gcphase == _GCoff), a span may transition from |
| // in-use to free (as a result of sweeping) or manual to free (as a |
| // result of stacks being freed). |
| // |
| // * During GC (gcphase != _GCoff), a span *must not* transition from |
| // manual or in-use to free. Because concurrent GC may read a pointer |
| // and then look up its span, the span state must be monotonic. |
| type mSpanState uint8 |
| |
| const ( |
| mSpanDead mSpanState = iota |
| mSpanInUse // allocated for garbage collected heap |
| mSpanManual // allocated for manual management (e.g., stack allocator) |
| mSpanFree |
| ) |
| |
| // mSpanStateNames are the names of the span states, indexed by |
| // mSpanState. |
| var mSpanStateNames = []string{ |
| "mSpanDead", |
| "mSpanInUse", |
| "mSpanManual", |
| "mSpanFree", |
| } |
| |
| // mSpanList heads a linked list of spans. |
| // |
| //go:notinheap |
| type mSpanList struct { |
| first *mspan // first span in list, or nil if none |
| last *mspan // last span in list, or nil if none |
| } |
| |
| //go:notinheap |
| type mspan struct { |
| next *mspan // next span in list, or nil if none |
| prev *mspan // previous span in list, or nil if none |
| list *mSpanList // For debugging. TODO: Remove. |
| |
| startAddr uintptr // address of first byte of span aka s.base() |
| npages uintptr // number of pages in span |
| |
| manualFreeList gclinkptr // list of free objects in mSpanManual spans |
| |
| // freeindex is the slot index between 0 and nelems at which to begin scanning |
| // for the next free object in this span. |
| // Each allocation scans allocBits starting at freeindex until it encounters a 0 |
| // indicating a free object. freeindex is then adjusted so that subsequent scans begin |
| // just past the newly discovered free object. |
| // |
| // If freeindex == nelem, this span has no free objects. |
| // |
| // allocBits is a bitmap of objects in this span. |
| // If n >= freeindex and allocBits[n/8] & (1<<(n%8)) is 0 |
| // then object n is free; |
| // otherwise, object n is allocated. Bits starting at nelem are |
| // undefined and should never be referenced. |
| // |
| // Object n starts at address n*elemsize + (start << pageShift). |
| freeindex uintptr |
| // TODO: Look up nelems from sizeclass and remove this field if it |
| // helps performance. |
| nelems uintptr // number of object in the span. |
| |
| // Cache of the allocBits at freeindex. allocCache is shifted |
| // such that the lowest bit corresponds to the bit freeindex. |
| // allocCache holds the complement of allocBits, thus allowing |
| // ctz (count trailing zero) to use it directly. |
| // allocCache may contain bits beyond s.nelems; the caller must ignore |
| // these. |
| allocCache uint64 |
| |
| // allocBits and gcmarkBits hold pointers to a span's mark and |
| // allocation bits. The pointers are 8 byte aligned. |
| // There are three arenas where this data is held. |
| // free: Dirty arenas that are no longer accessed |
| // and can be reused. |
| // next: Holds information to be used in the next GC cycle. |
| // current: Information being used during this GC cycle. |
| // previous: Information being used during the last GC cycle. |
| // A new GC cycle starts with the call to finishsweep_m. |
| // finishsweep_m moves the previous arena to the free arena, |
| // the current arena to the previous arena, and |
| // the next arena to the current arena. |
| // The next arena is populated as the spans request |
| // memory to hold gcmarkBits for the next GC cycle as well |
| // as allocBits for newly allocated spans. |
| // |
| // The pointer arithmetic is done "by hand" instead of using |
| // arrays to avoid bounds checks along critical performance |
| // paths. |
| // The sweep will free the old allocBits and set allocBits to the |
| // gcmarkBits. The gcmarkBits are replaced with a fresh zeroed |
| // out memory. |
| allocBits *gcBits |
| gcmarkBits *gcBits |
| |
| // sweep generation: |
| // if sweepgen == h->sweepgen - 2, the span needs sweeping |
| // if sweepgen == h->sweepgen - 1, the span is currently being swept |
| // if sweepgen == h->sweepgen, the span is swept and ready to use |
| // if sweepgen == h->sweepgen + 1, the span was cached before sweep began and is still cached, and needs sweeping |
| // if sweepgen == h->sweepgen + 3, the span was swept and then cached and is still cached |
| // h->sweepgen is incremented by 2 after every GC |
| |
| sweepgen uint32 |
| divMul uint16 // for divide by elemsize - divMagic.mul |
| baseMask uint16 // if non-0, elemsize is a power of 2, & this will get object allocation base |
| allocCount uint16 // number of allocated objects |
| spanclass spanClass // size class and noscan (uint8) |
| state mSpanState // mspaninuse etc |
| needzero uint8 // needs to be zeroed before allocation |
| divShift uint8 // for divide by elemsize - divMagic.shift |
| divShift2 uint8 // for divide by elemsize - divMagic.shift2 |
| scavenged bool // whether this span has had its pages released to the OS |
| elemsize uintptr // computed from sizeclass or from npages |
| unusedsince int64 // first time spotted by gc in mspanfree state |
| limit uintptr // end of data in span |
| speciallock mutex // guards specials list |
| specials *special // linked list of special records sorted by offset. |
| } |
| |
| func (s *mspan) base() uintptr { |
| return s.startAddr |
| } |
| |
| func (s *mspan) layout() (size, n, total uintptr) { |
| total = s.npages << _PageShift |
| size = s.elemsize |
| if size > 0 { |
| n = total / size |
| } |
| return |
| } |
| |
| // physPageBounds returns the start and end of the span |
| // rounded in to the physical page size. |
| func (s *mspan) physPageBounds() (uintptr, uintptr) { |
| start := s.base() |
| end := start + s.npages<<_PageShift |
| if physPageSize > _PageSize { |
| // Round start and end in. |
| start = (start + physPageSize - 1) &^ (physPageSize - 1) |
| end &^= physPageSize - 1 |
| } |
| return start, end |
| } |
| |
| func (h *mheap) coalesce(s *mspan) { |
| // We scavenge s at the end after coalescing if s or anything |
| // it merged with is marked scavenged. |
| needsScavenge := false |
| prescavenged := s.released() // number of bytes already scavenged. |
| |
| // merge is a helper which merges other into s, deletes references to other |
| // in heap metadata, and then discards it. other must be adjacent to s. |
| merge := func(other *mspan) { |
| // Adjust s via base and npages and also in heap metadata. |
| s.npages += other.npages |
| s.needzero |= other.needzero |
| if other.startAddr < s.startAddr { |
| s.startAddr = other.startAddr |
| h.setSpan(s.base(), s) |
| } else { |
| h.setSpan(s.base()+s.npages*pageSize-1, s) |
| } |
| |
| // If before or s are scavenged, then we need to scavenge the final coalesced span. |
| needsScavenge = needsScavenge || other.scavenged || s.scavenged |
| prescavenged += other.released() |
| |
| // The size is potentially changing so the treap needs to delete adjacent nodes and |
| // insert back as a combined node. |
| if other.scavenged { |
| h.scav.removeSpan(other) |
| } else { |
| h.free.removeSpan(other) |
| } |
| other.state = mSpanDead |
| h.spanalloc.free(unsafe.Pointer(other)) |
| } |
| |
| // realign is a helper which shrinks other and grows s such that their |
| // boundary is on a physical page boundary. |
| realign := func(a, b, other *mspan) { |
| // Caller must ensure a.startAddr < b.startAddr and that either a or |
| // b is s. a and b must be adjacent. other is whichever of the two is |
| // not s. |
| |
| // If pageSize <= physPageSize then spans are always aligned |
| // to physical page boundaries, so just exit. |
| if pageSize <= physPageSize { |
| return |
| } |
| // Since we're resizing other, we must remove it from the treap. |
| if other.scavenged { |
| h.scav.removeSpan(other) |
| } else { |
| h.free.removeSpan(other) |
| } |
| // Round boundary to the nearest physical page size, toward the |
| // scavenged span. |
| boundary := b.startAddr |
| if a.scavenged { |
| boundary &^= (physPageSize - 1) |
| } else { |
| boundary = (boundary + physPageSize - 1) &^ (physPageSize - 1) |
| } |
| a.npages = (boundary - a.startAddr) / pageSize |
| b.npages = (b.startAddr + b.npages*pageSize - boundary) / pageSize |
| b.startAddr = boundary |
| |
| h.setSpan(boundary-1, a) |
| h.setSpan(boundary, b) |
| |
| // Re-insert other now that it has a new size. |
| if other.scavenged { |
| h.scav.insert(other) |
| } else { |
| h.free.insert(other) |
| } |
| } |
| |
| // Coalesce with earlier, later spans. |
| if before := spanOf(s.base() - 1); before != nil && before.state == mSpanFree { |
| if s.scavenged == before.scavenged { |
| merge(before) |
| } else { |
| realign(before, s, before) |
| } |
| } |
| |
| // Now check to see if next (greater addresses) span is free and can be coalesced. |
| if after := spanOf(s.base() + s.npages*pageSize); after != nil && after.state == mSpanFree { |
| if s.scavenged == after.scavenged { |
| merge(after) |
| } else { |
| realign(s, after, after) |
| } |
| } |
| |
| if needsScavenge { |
| // When coalescing spans, some physical pages which |
| // were not returned to the OS previously because |
| // they were only partially covered by the span suddenly |
| // become available for scavenging. We want to make sure |
| // those holes are filled in, and the span is properly |
| // scavenged. Rather than trying to detect those holes |
| // directly, we collect how many bytes were already |
| // scavenged above and subtract that from heap_released |
| // before re-scavenging the entire newly-coalesced span, |
| // which will implicitly bump up heap_released. |
| memstats.heap_released -= uint64(prescavenged) |
| s.scavenge() |
| } |
| } |
| |
| func (s *mspan) scavenge() uintptr { |
| // start and end must be rounded in, otherwise madvise |
| // will round them *out* and release more memory |
| // than we want. |
| start, end := s.physPageBounds() |
| if end <= start { |
| // start and end don't span a whole physical page. |
| return 0 |
| } |
| released := end - start |
| memstats.heap_released += uint64(released) |
| s.scavenged = true |
| sysUnused(unsafe.Pointer(start), released) |
| return released |
| } |
| |
| // released returns the number of bytes in this span |
| // which were returned back to the OS. |
| func (s *mspan) released() uintptr { |
| if !s.scavenged { |
| return 0 |
| } |
| start, end := s.physPageBounds() |
| return end - start |
| } |
| |
| // recordspan adds a newly allocated span to h.allspans. |
| // |
| // This only happens the first time a span is allocated from |
| // mheap.spanalloc (it is not called when a span is reused). |
| // |
| // Write barriers are disallowed here because it can be called from |
| // gcWork when allocating new workbufs. However, because it's an |
| // indirect call from the fixalloc initializer, the compiler can't see |
| // this. |
| // |
| //go:nowritebarrierrec |
| func recordspan(vh unsafe.Pointer, p unsafe.Pointer) { |
| h := (*mheap)(vh) |
| s := (*mspan)(p) |
| if len(h.allspans) >= cap(h.allspans) { |
| n := 64 * 1024 / sys.PtrSize |
| if n < cap(h.allspans)*3/2 { |
| n = cap(h.allspans) * 3 / 2 |
| } |
| var new []*mspan |
| sp := (*slice)(unsafe.Pointer(&new)) |
| sp.array = sysAlloc(uintptr(n)*sys.PtrSize, &memstats.other_sys) |
| if sp.array == nil { |
| throw("runtime: cannot allocate memory") |
| } |
| sp.len = len(h.allspans) |
| sp.cap = n |
| if len(h.allspans) > 0 { |
| copy(new, h.allspans) |
| } |
| oldAllspans := h.allspans |
| *(*notInHeapSlice)(unsafe.Pointer(&h.allspans)) = *(*notInHeapSlice)(unsafe.Pointer(&new)) |
| if len(oldAllspans) != 0 { |
| sysFree(unsafe.Pointer(&oldAllspans[0]), uintptr(cap(oldAllspans))*unsafe.Sizeof(oldAllspans[0]), &memstats.other_sys) |
| } |
| } |
| h.allspans = h.allspans[:len(h.allspans)+1] |
| h.allspans[len(h.allspans)-1] = s |
| } |
| |
| // A spanClass represents the size class and noscan-ness of a span. |
| // |
| // Each size class has a noscan spanClass and a scan spanClass. The |
| // noscan spanClass contains only noscan objects, which do not contain |
| // pointers and thus do not need to be scanned by the garbage |
| // collector. |
| type spanClass uint8 |
| |
| const ( |
| numSpanClasses = _NumSizeClasses << 1 |
| tinySpanClass = spanClass(tinySizeClass<<1 | 1) |
| ) |
| |
| func makeSpanClass(sizeclass uint8, noscan bool) spanClass { |
| return spanClass(sizeclass<<1) | spanClass(bool2int(noscan)) |
| } |
| |
| func (sc spanClass) sizeclass() int8 { |
| return int8(sc >> 1) |
| } |
| |
| func (sc spanClass) noscan() bool { |
| return sc&1 != 0 |
| } |
| |
| // arenaIndex returns the index into mheap_.arenas of the arena |
| // containing metadata for p. This index combines of an index into the |
| // L1 map and an index into the L2 map and should be used as |
| // mheap_.arenas[ai.l1()][ai.l2()]. |
| // |
| // If p is outside the range of valid heap addresses, either l1() or |
| // l2() will be out of bounds. |
| // |
| // It is nosplit because it's called by spanOf and several other |
| // nosplit functions. |
| // |
| //go:nosplit |
| func arenaIndex(p uintptr) arenaIdx { |
| return arenaIdx((p + arenaBaseOffset) / heapArenaBytes) |
| } |
| |
| // arenaBase returns the low address of the region covered by heap |
| // arena i. |
| func arenaBase(i arenaIdx) uintptr { |
| return uintptr(i)*heapArenaBytes - arenaBaseOffset |
| } |
| |
| type arenaIdx uint |
| |
| func (i arenaIdx) l1() uint { |
| if arenaL1Bits == 0 { |
| // Let the compiler optimize this away if there's no |
| // L1 map. |
| return 0 |
| } else { |
| return uint(i) >> arenaL1Shift |
| } |
| } |
| |
| func (i arenaIdx) l2() uint { |
| if arenaL1Bits == 0 { |
| return uint(i) |
| } else { |
| return uint(i) & (1<<arenaL2Bits - 1) |
| } |
| } |
| |
| // inheap reports whether b is a pointer into a (potentially dead) heap object. |
| // It returns false for pointers into mSpanManual spans. |
| // Non-preemptible because it is used by write barriers. |
| //go:nowritebarrier |
| //go:nosplit |
| func inheap(b uintptr) bool { |
| return spanOfHeap(b) != nil |
| } |
| |
| // inHeapOrStack is a variant of inheap that returns true for pointers |
| // into any allocated heap span. |
| // |
| //go:nowritebarrier |
| //go:nosplit |
| func inHeapOrStack(b uintptr) bool { |
| s := spanOf(b) |
| if s == nil || b < s.base() { |
| return false |
| } |
| switch s.state { |
| case mSpanInUse, mSpanManual: |
| return b < s.limit |
| default: |
| return false |
| } |
| } |
| |
| // spanOf returns the span of p. If p does not point into the heap |
| // arena or no span has ever contained p, spanOf returns nil. |
| // |
| // If p does not point to allocated memory, this may return a non-nil |
| // span that does *not* contain p. If this is a possibility, the |
| // caller should either call spanOfHeap or check the span bounds |
| // explicitly. |
| // |
| // Must be nosplit because it has callers that are nosplit. |
| // |
| //go:nosplit |
| func spanOf(p uintptr) *mspan { |
| // This function looks big, but we use a lot of constant |
| // folding around arenaL1Bits to get it under the inlining |
| // budget. Also, many of the checks here are safety checks |
| // that Go needs to do anyway, so the generated code is quite |
| // short. |
| ri := arenaIndex(p) |
| if arenaL1Bits == 0 { |
| // If there's no L1, then ri.l1() can't be out of bounds but ri.l2() can. |
| if ri.l2() >= uint(len(mheap_.arenas[0])) { |
| return nil |
| } |
| } else { |
| // If there's an L1, then ri.l1() can be out of bounds but ri.l2() can't. |
| if ri.l1() >= uint(len(mheap_.arenas)) { |
| return nil |
| } |
| } |
| l2 := mheap_.arenas[ri.l1()] |
| if arenaL1Bits != 0 && l2 == nil { // Should never happen if there's no L1. |
| return nil |
| } |
| ha := l2[ri.l2()] |
| if ha == nil { |
| return nil |
| } |
| return ha.spans[(p/pageSize)%pagesPerArena] |
| } |
| |
| // spanOfUnchecked is equivalent to spanOf, but the caller must ensure |
| // that p points into an allocated heap arena. |
| // |
| // Must be nosplit because it has callers that are nosplit. |
| // |
| //go:nosplit |
| func spanOfUnchecked(p uintptr) *mspan { |
| ai := arenaIndex(p) |
| return mheap_.arenas[ai.l1()][ai.l2()].spans[(p/pageSize)%pagesPerArena] |
| } |
| |
| // spanOfHeap is like spanOf, but returns nil if p does not point to a |
| // heap object. |
| // |
| // Must be nosplit because it has callers that are nosplit. |
| // |
| //go:nosplit |
| func spanOfHeap(p uintptr) *mspan { |
| s := spanOf(p) |
| // If p is not allocated, it may point to a stale span, so we |
| // have to check the span's bounds and state. |
| if s == nil || p < s.base() || p >= s.limit || s.state != mSpanInUse { |
| return nil |
| } |
| return s |
| } |
| |
| // pageIndexOf returns the arena, page index, and page mask for pointer p. |
| // The caller must ensure p is in the heap. |
| func pageIndexOf(p uintptr) (arena *heapArena, pageIdx uintptr, pageMask uint8) { |
| ai := arenaIndex(p) |
| arena = mheap_.arenas[ai.l1()][ai.l2()] |
| pageIdx = ((p / pageSize) / 8) % uintptr(len(arena.pageInUse)) |
| pageMask = byte(1 << ((p / pageSize) % 8)) |
| return |
| } |
| |
| // Initialize the heap. |
| func (h *mheap) init() { |
| h.treapalloc.init(unsafe.Sizeof(treapNode{}), nil, nil, &memstats.other_sys) |
| h.spanalloc.init(unsafe.Sizeof(mspan{}), recordspan, unsafe.Pointer(h), &memstats.mspan_sys) |
| h.cachealloc.init(unsafe.Sizeof(mcache{}), nil, nil, &memstats.mcache_sys) |
| h.specialfinalizeralloc.init(unsafe.Sizeof(specialfinalizer{}), nil, nil, &memstats.other_sys) |
| h.specialprofilealloc.init(unsafe.Sizeof(specialprofile{}), nil, nil, &memstats.other_sys) |
| h.arenaHintAlloc.init(unsafe.Sizeof(arenaHint{}), nil, nil, &memstats.other_sys) |
| |
| // Don't zero mspan allocations. Background sweeping can |
| // inspect a span concurrently with allocating it, so it's |
| // important that the span's sweepgen survive across freeing |
| // and re-allocating a span to prevent background sweeping |
| // from improperly cas'ing it from 0. |
| // |
| // This is safe because mspan contains no heap pointers. |
| h.spanalloc.zero = false |
| |
| // h->mapcache needs no init |
| |
| for i := range h.central { |
| h.central[i].mcentral.init(spanClass(i)) |
| } |
| } |
| |
| // reclaim sweeps and reclaims at least npage pages into the heap. |
| // It is called before allocating npage pages to keep growth in check. |
| // |
| // reclaim implements the page-reclaimer half of the sweeper. |
| // |
| // h must NOT be locked. |
| func (h *mheap) reclaim(npage uintptr) { |
| // This scans pagesPerChunk at a time. Higher values reduce |
| // contention on h.reclaimPos, but increase the minimum |
| // latency of performing a reclaim. |
| // |
| // Must be a multiple of the pageInUse bitmap element size. |
| // |
| // The time required by this can vary a lot depending on how |
| // many spans are actually freed. Experimentally, it can scan |
| // for pages at ~300 GB/ms on a 2.6GHz Core i7, but can only |
| // free spans at ~32 MB/ms. Using 512 pages bounds this at |
| // roughly 100µs. |
| // |
| // TODO(austin): Half of the time spent freeing spans is in |
| // locking/unlocking the heap (even with low contention). We |
| // could make the slow path here several times faster by |
| // batching heap frees. |
| const pagesPerChunk = 512 |
| |
| // Bail early if there's no more reclaim work. |
| if atomic.Load64(&h.reclaimIndex) >= 1<<63 { |
| return |
| } |
| |
| // Disable preemption so the GC can't start while we're |
| // sweeping, so we can read h.sweepArenas, and so |
| // traceGCSweepStart/Done pair on the P. |
| mp := acquirem() |
| |
| if trace.enabled { |
| traceGCSweepStart() |
| } |
| |
| arenas := h.sweepArenas |
| locked := false |
| for npage > 0 { |
| // Pull from accumulated credit first. |
| if credit := atomic.Loaduintptr(&h.reclaimCredit); credit > 0 { |
| take := credit |
| if take > npage { |
| // Take only what we need. |
| take = npage |
| } |
| if atomic.Casuintptr(&h.reclaimCredit, credit, credit-take) { |
| npage -= take |
| } |
| continue |
| } |
| |
| // Claim a chunk of work. |
| idx := uintptr(atomic.Xadd64(&h.reclaimIndex, pagesPerChunk) - pagesPerChunk) |
| if idx/pagesPerArena >= uintptr(len(arenas)) { |
| // Page reclaiming is done. |
| atomic.Store64(&h.reclaimIndex, 1<<63) |
| break |
| } |
| |
| if !locked { |
| // Lock the heap for reclaimChunk. |
| lock(&h.lock) |
| locked = true |
| } |
| |
| // Scan this chunk. |
| nfound := h.reclaimChunk(arenas, idx, pagesPerChunk) |
| if nfound <= npage { |
| npage -= nfound |
| } else { |
| // Put spare pages toward global credit. |
| atomic.Xadduintptr(&h.reclaimCredit, nfound-npage) |
| npage = 0 |
| } |
| } |
| if locked { |
| unlock(&h.lock) |
| } |
| |
| if trace.enabled { |
| traceGCSweepDone() |
| } |
| releasem(mp) |
| } |
| |
| // reclaimChunk sweeps unmarked spans that start at page indexes [pageIdx, pageIdx+n). |
| // It returns the number of pages returned to the heap. |
| // |
| // h.lock must be held and the caller must be non-preemptible. |
| func (h *mheap) reclaimChunk(arenas []arenaIdx, pageIdx, n uintptr) uintptr { |
| // The heap lock must be held because this accesses the |
| // heapArena.spans arrays using potentially non-live pointers. |
| // In particular, if a span were freed and merged concurrently |
| // with this probing heapArena.spans, it would be possible to |
| // observe arbitrary, stale span pointers. |
| n0 := n |
| var nFreed uintptr |
| sg := h.sweepgen |
| for n > 0 { |
| ai := arenas[pageIdx/pagesPerArena] |
| ha := h.arenas[ai.l1()][ai.l2()] |
| |
| // Get a chunk of the bitmap to work on. |
| arenaPage := uint(pageIdx % pagesPerArena) |
| inUse := ha.pageInUse[arenaPage/8:] |
| marked := ha.pageMarks[arenaPage/8:] |
| if uintptr(len(inUse)) > n/8 { |
| inUse = inUse[:n/8] |
| marked = marked[:n/8] |
| } |
| |
| // Scan this bitmap chunk for spans that are in-use |
| // but have no marked objects on them. |
| for i := range inUse { |
| inUseUnmarked := inUse[i] &^ marked[i] |
| if inUseUnmarked == 0 { |
| continue |
| } |
| |
| for j := uint(0); j < 8; j++ { |
| if inUseUnmarked&(1<<j) != 0 { |
| s := ha.spans[arenaPage+uint(i)*8+j] |
| if atomic.Load(&s.sweepgen) == sg-2 && atomic.Cas(&s.sweepgen, sg-2, sg-1) { |
| npages := s.npages |
| unlock(&h.lock) |
| if s.sweep(false) { |
| nFreed += npages |
| } |
| lock(&h.lock) |
| // Reload inUse. It's possible nearby |
| // spans were freed when we dropped the |
| // lock and we don't want to get stale |
| // pointers from the spans array. |
| inUseUnmarked = inUse[i] &^ marked[i] |
| } |
| } |
| } |
| } |
| |
| // Advance. |
| pageIdx += uintptr(len(inUse) * 8) |
| n -= uintptr(len(inUse) * 8) |
| } |
| if trace.enabled { |
| // Account for pages scanned but not reclaimed. |
| traceGCSweepSpan((n0 - nFreed) * pageSize) |
| } |
| return nFreed |
| } |
| |
| // alloc_m is the internal implementation of mheap.alloc. |
| // |
| // alloc_m must run on the system stack because it locks the heap, so |
| // any stack growth during alloc_m would self-deadlock. |
| // |
| //go:systemstack |
| func (h *mheap) alloc_m(npage uintptr, spanclass spanClass, large bool) *mspan { |
| _g_ := getg() |
| |
| // To prevent excessive heap growth, before allocating n pages |
| // we need to sweep and reclaim at least n pages. |
| if h.sweepdone == 0 { |
| h.reclaim(npage) |
| } |
| |
| lock(&h.lock) |
| // transfer stats from cache to global |
| memstats.heap_scan += uint64(_g_.m.mcache.local_scan) |
| _g_.m.mcache.local_scan = 0 |
| memstats.tinyallocs += uint64(_g_.m.mcache.local_tinyallocs) |
| _g_.m.mcache.local_tinyallocs = 0 |
| |
| s := h.allocSpanLocked(npage, &memstats.heap_inuse) |
| if s != nil { |
| // Record span info, because gc needs to be |
| // able to map interior pointer to containing span. |
| atomic.Store(&s.sweepgen, h.sweepgen) |
| h.sweepSpans[h.sweepgen/2%2].push(s) // Add to swept in-use list. |
| s.state = mSpanInUse |
| s.allocCount = 0 |
| s.spanclass = spanclass |
| if sizeclass := spanclass.sizeclass(); sizeclass == 0 { |
| s.elemsize = s.npages << _PageShift |
| s.divShift = 0 |
| s.divMul = 0 |
| s.divShift2 = 0 |
| s.baseMask = 0 |
| } else { |
| s.elemsize = uintptr(class_to_size[sizeclass]) |
| m := &class_to_divmagic[sizeclass] |
| s.divShift = m.shift |
| s.divMul = m.mul |
| s.divShift2 = m.shift2 |
| s.baseMask = m.baseMask |
| } |
| |
| // Mark in-use span in arena page bitmap. |
| arena, pageIdx, pageMask := pageIndexOf(s.base()) |
| arena.pageInUse[pageIdx] |= pageMask |
| |
| // update stats, sweep lists |
| h.pagesInUse += uint64(npage) |
| if large { |
| memstats.heap_objects++ |
| mheap_.largealloc += uint64(s.elemsize) |
| mheap_.nlargealloc++ |
| atomic.Xadd64(&memstats.heap_live, int64(npage<<_PageShift)) |
| } |
| } |
| // heap_scan and heap_live were updated. |
| if gcBlackenEnabled != 0 { |
| gcController.revise() |
| } |
| |
| if trace.enabled { |
| traceHeapAlloc() |
| } |
| |
| // h.spans is accessed concurrently without synchronization |
| // from other threads. Hence, there must be a store/store |
| // barrier here to ensure the writes to h.spans above happen |
| // before the caller can publish a pointer p to an object |
| // allocated from s. As soon as this happens, the garbage |
| // collector running on another processor could read p and |
| // look up s in h.spans. The unlock acts as the barrier to |
| // order these writes. On the read side, the data dependency |
| // between p and the index in h.spans orders the reads. |
| unlock(&h.lock) |
| return s |
| } |
| |
| // alloc allocates a new span of npage pages from the GC'd heap. |
| // |
| // Either large must be true or spanclass must indicates the span's |
| // size class and scannability. |
| // |
| // If needzero is true, the memory for the returned span will be zeroed. |
| func (h *mheap) alloc(npage uintptr, spanclass spanClass, large bool, needzero bool) *mspan { |
| // Don't do any operations that lock the heap on the G stack. |
| // It might trigger stack growth, and the stack growth code needs |
| // to be able to allocate heap. |
| var s *mspan |
| systemstack(func() { |
| s = h.alloc_m(npage, spanclass, large) |
| }) |
| |
| if s != nil { |
| if needzero && s.needzero != 0 { |
| memclrNoHeapPointers(unsafe.Pointer(s.base()), s.npages<<_PageShift) |
| } |
| s.needzero = 0 |
| } |
| return s |
| } |
| |
| // allocManual allocates a manually-managed span of npage pages. |
| // allocManual returns nil if allocation fails. |
| // |
| // allocManual adds the bytes used to *stat, which should be a |
| // memstats in-use field. Unlike allocations in the GC'd heap, the |
| // allocation does *not* count toward heap_inuse or heap_sys. |
| // |
| // The memory backing the returned span may not be zeroed if |
| // span.needzero is set. |
| // |
| // allocManual must be called on the system stack to prevent stack |
| // growth. Since this is used by the stack allocator, stack growth |
| // during allocManual would self-deadlock. |
| // |
| //go:systemstack |
| func (h *mheap) allocManual(npage uintptr, stat *uint64) *mspan { |
| lock(&h.lock) |
| s := h.allocSpanLocked(npage, stat) |
| if s != nil { |
| s.state = mSpanManual |
| s.manualFreeList = 0 |
| s.allocCount = 0 |
| s.spanclass = 0 |
| s.nelems = 0 |
| s.elemsize = 0 |
| s.limit = s.base() + s.npages<<_PageShift |
| // Manually managed memory doesn't count toward heap_sys. |
| memstats.heap_sys -= uint64(s.npages << _PageShift) |
| } |
| |
| // This unlock acts as a release barrier. See mheap.alloc_m. |
| unlock(&h.lock) |
| |
| return s |
| } |
| |
| // setSpan modifies the span map so spanOf(base) is s. |
| func (h *mheap) setSpan(base uintptr, s *mspan) { |
| ai := arenaIndex(base) |
| h.arenas[ai.l1()][ai.l2()].spans[(base/pageSize)%pagesPerArena] = s |
| } |
| |
| // setSpans modifies the span map so [spanOf(base), spanOf(base+npage*pageSize)) |
| // is s. |
| func (h *mheap) setSpans(base, npage uintptr, s *mspan) { |
| p := base / pageSize |
| ai := arenaIndex(base) |
| ha := h.arenas[ai.l1()][ai.l2()] |
| for n := uintptr(0); n < npage; n++ { |
| i := (p + n) % pagesPerArena |
| if i == 0 { |
| ai = arenaIndex(base + n*pageSize) |
| ha = h.arenas[ai.l1()][ai.l2()] |
| } |
| ha.spans[i] = s |
| } |
| } |
| |
| // pickFreeSpan acquires a free span from internal free list |
| // structures if one is available. Otherwise returns nil. |
| // h must be locked. |
| func (h *mheap) pickFreeSpan(npage uintptr) *mspan { |
| tf := h.free.find(npage) |
| ts := h.scav.find(npage) |
| |
| // Check for whichever treap gave us the smaller, non-nil result. |
| // Note that we want the _smaller_ free span, i.e. the free span |
| // closer in size to the amount we requested (npage). |
| var s *mspan |
| if tf != nil && (ts == nil || tf.spanKey.npages <= ts.spanKey.npages) { |
| s = tf.spanKey |
| h.free.removeNode(tf) |
| } else if ts != nil && (tf == nil || tf.spanKey.npages > ts.spanKey.npages) { |
| s = ts.spanKey |
| h.scav.removeNode(ts) |
| } |
| return s |
| } |
| |
| // Allocates a span of the given size. h must be locked. |
| // The returned span has been removed from the |
| // free structures, but its state is still mSpanFree. |
| func (h *mheap) allocSpanLocked(npage uintptr, stat *uint64) *mspan { |
| var s *mspan |
| |
| s = h.pickFreeSpan(npage) |
| if s != nil { |
| goto HaveSpan |
| } |
| // On failure, grow the heap and try again. |
| if !h.grow(npage) { |
| return nil |
| } |
| s = h.pickFreeSpan(npage) |
| if s != nil { |
| goto HaveSpan |
| } |
| throw("grew heap, but no adequate free span found") |
| |
| HaveSpan: |
| // Mark span in use. |
| if s.state != mSpanFree { |
| throw("candidate mspan for allocation is not free") |
| } |
| if s.npages < npage { |
| throw("candidate mspan for allocation is too small") |
| } |
| |
| // First, subtract any memory that was released back to |
| // the OS from s. We will re-scavenge the trimmed section |
| // if necessary. |
| memstats.heap_released -= uint64(s.released()) |
| |
| if s.npages > npage { |
| // Trim extra and put it back in the heap. |
| t := (*mspan)(h.spanalloc.alloc()) |
| t.init(s.base()+npage<<_PageShift, s.npages-npage) |
| s.npages = npage |
| h.setSpan(t.base()-1, s) |
| h.setSpan(t.base(), t) |
| h.setSpan(t.base()+t.npages*pageSize-1, t) |
| t.needzero = s.needzero |
| // If s was scavenged, then t may be scavenged. |
| start, end := t.physPageBounds() |
| if s.scavenged && start < end { |
| memstats.heap_released += uint64(end - start) |
| t.scavenged = true |
| } |
| s.state = mSpanManual // prevent coalescing with s |
| t.state = mSpanManual |
| h.freeSpanLocked(t, false, false, s.unusedsince) |
| s.state = mSpanFree |
| } |
| // "Unscavenge" s only AFTER splitting so that |
| // we only sysUsed whatever we actually need. |
| if s.scavenged { |
| // sysUsed all the pages that are actually available |
| // in the span. Note that we don't need to decrement |
| // heap_released since we already did so earlier. |
| sysUsed(unsafe.Pointer(s.base()), s.npages<<_PageShift) |
| s.scavenged = false |
| } |
| s.unusedsince = 0 |
| |
| h.setSpans(s.base(), npage, s) |
| |
| *stat += uint64(npage << _PageShift) |
| memstats.heap_idle -= uint64(npage << _PageShift) |
| |
| //println("spanalloc", hex(s.start<<_PageShift)) |
| if s.inList() { |
| throw("still in list") |
| } |
| return s |
| } |
| |
| // Try to add at least npage pages of memory to the heap, |
| // returning whether it worked. |
| // |
| // h must be locked. |
| func (h *mheap) grow(npage uintptr) bool { |
| ask := npage << _PageShift |
| v, size := h.sysAlloc(ask) |
| if v == nil { |
| print("runtime: out of memory: cannot allocate ", ask, "-byte block (", memstats.heap_sys, " in use)\n") |
| return false |
| } |
| |
| // Scavenge some pages out of the free treap to make up for |
| // the virtual memory space we just allocated. We prefer to |
| // scavenge the largest spans first since the cost of scavenging |
| // is proportional to the number of sysUnused() calls rather than |
| // the number of pages released, so we make fewer of those calls |
| // with larger spans. |
| h.scavengeLargest(size) |
| |
| // Create a fake "in use" span and free it, so that the |
| // right coalescing happens. |
| s := (*mspan)(h.spanalloc.alloc()) |
| s.init(uintptr(v), size/pageSize) |
| h.setSpans(s.base(), s.npages, s) |
| atomic.Store(&s.sweepgen, h.sweepgen) |
| s.state = mSpanInUse |
| h.pagesInUse += uint64(s.npages) |
| h.freeSpanLocked(s, false, true, 0) |
| return true |
| } |
| |
| // Free the span back into the heap. |
| // |
| // large must match the value of large passed to mheap.alloc. This is |
| // used for accounting. |
| func (h *mheap) freeSpan(s *mspan, large bool) { |
| systemstack(func() { |
| mp := getg().m |
| lock(&h.lock) |
| memstats.heap_scan += uint64(mp.mcache.local_scan) |
| mp.mcache.local_scan = 0 |
| memstats.tinyallocs += uint64(mp.mcache.local_tinyallocs) |
| mp.mcache.local_tinyallocs = 0 |
| if msanenabled { |
| // Tell msan that this entire span is no longer in use. |
| base := unsafe.Pointer(s.base()) |
| bytes := s.npages << _PageShift |
| msanfree(base, bytes) |
| } |
| if large { |
| // Match accounting done in mheap.alloc. |
| memstats.heap_objects-- |
| } |
| if gcBlackenEnabled != 0 { |
| // heap_scan changed. |
| gcController.revise() |
| } |
| h.freeSpanLocked(s, true, true, 0) |
| unlock(&h.lock) |
| }) |
| } |
| |
| // freeManual frees a manually-managed span returned by allocManual. |
| // stat must be the same as the stat passed to the allocManual that |
| // allocated s. |
| // |
| // This must only be called when gcphase == _GCoff. See mSpanState for |
| // an explanation. |
| // |
| // freeManual must be called on the system stack to prevent stack |
| // growth, just like allocManual. |
| // |
| //go:systemstack |
| func (h *mheap) freeManual(s *mspan, stat *uint64) { |
| s.needzero = 1 |
| lock(&h.lock) |
| *stat -= uint64(s.npages << _PageShift) |
| memstats.heap_sys += uint64(s.npages << _PageShift) |
| h.freeSpanLocked(s, false, true, 0) |
| unlock(&h.lock) |
| } |
| |
| // s must be on the busy list or unlinked. |
| func (h *mheap) freeSpanLocked(s *mspan, acctinuse, acctidle bool, unusedsince int64) { |
| switch s.state { |
| case mSpanManual: |
| if s.allocCount != 0 { |
| throw("mheap.freeSpanLocked - invalid stack free") |
| } |
| case mSpanInUse: |
| if s.allocCount != 0 || s.sweepgen != h.sweepgen { |
| print("mheap.freeSpanLocked - span ", s, " ptr ", hex(s.base()), " allocCount ", s.allocCount, " sweepgen ", s.sweepgen, "/", h.sweepgen, "\n") |
| throw("mheap.freeSpanLocked - invalid free") |
| } |
| h.pagesInUse -= uint64(s.npages) |
| |
| // Clear in-use bit in arena page bitmap. |
| arena, pageIdx, pageMask := pageIndexOf(s.base()) |
| arena.pageInUse[pageIdx] &^= pageMask |
| default: |
| throw("mheap.freeSpanLocked - invalid span state") |
| } |
| |
| if acctinuse { |
| memstats.heap_inuse -= uint64(s.npages << _PageShift) |
| } |
| if acctidle { |
| memstats.heap_idle += uint64(s.npages << _PageShift) |
| } |
| s.state = mSpanFree |
| |
| // Stamp newly unused spans. The scavenger will use that |
| // info to potentially give back some pages to the OS. |
| s.unusedsince = unusedsince |
| if unusedsince == 0 { |
| s.unusedsince = nanotime() |
| } |
| |
| // Coalesce span with neighbors. |
| h.coalesce(s) |
| |
| // Insert s into the appropriate treap. |
| if s.scavenged { |
| h.scav.insert(s) |
| } else { |
| h.free.insert(s) |
| } |
| } |
| |
| // scavengeLargest scavenges nbytes worth of spans in unscav |
| // starting from the largest span and working down. It then takes those spans |
| // and places them in scav. h must be locked. |
| func (h *mheap) scavengeLargest(nbytes uintptr) { |
| // Use up scavenge credit if there's any available. |
| if nbytes > h.scavengeCredit { |
| nbytes -= h.scavengeCredit |
| h.scavengeCredit = 0 |
| } else { |
| h.scavengeCredit -= nbytes |
| return |
| } |
| // Iterate over the treap backwards (from largest to smallest) scavenging spans |
| // until we've reached our quota of nbytes. |
| released := uintptr(0) |
| for t := h.free.end(); released < nbytes && t.valid(); { |
| s := t.span() |
| r := s.scavenge() |
| if r == 0 { |
| // Since we're going in order of largest-to-smallest span, this |
| // means all other spans are no bigger than s. There's a high |
| // chance that the other spans don't even cover a full page, |
| // (though they could) but iterating further just for a handful |
| // of pages probably isn't worth it, so just stop here. |
| // |
| // This check also preserves the invariant that spans that have |
| // `scavenged` set are only ever in the `scav` treap, and |
| // those which have it unset are only in the `free` treap. |
| return |
| } |
| n := t.prev() |
| h.free.erase(t) |
| // Now that s is scavenged, we must eagerly coalesce it |
| // with its neighbors to prevent having two spans with |
| // the same scavenged state adjacent to each other. |
| h.coalesce(s) |
| t = n |
| h.scav.insert(s) |
| released += r |
| } |
| // If we over-scavenged, turn that extra amount into credit. |
| if released > nbytes { |
| h.scavengeCredit += released - nbytes |
| } |
| } |
| |
| // scavengeAll visits each node in the unscav treap and scavenges the |
| // treapNode's span. It then removes the scavenged span from |
| // unscav and adds it into scav before continuing. h must be locked. |
| func (h *mheap) scavengeAll(now, limit uint64) uintptr { |
| // Iterate over the treap scavenging spans if unused for at least limit time. |
| released := uintptr(0) |
| for t := h.free.start(); t.valid(); { |
| s := t.span() |
| n := t.next() |
| if (now - uint64(s.unusedsince)) > limit { |
| r := s.scavenge() |
| if r != 0 { |
| h.free.erase(t) |
| // Now that s is scavenged, we must eagerly coalesce it |
| // with its neighbors to prevent having two spans with |
| // the same scavenged state adjacent to each other. |
| h.coalesce(s) |
| h.scav.insert(s) |
| released += r |
| } |
| } |
| t = n |
| } |
| return released |
| } |
| |
| func (h *mheap) scavenge(k int32, now, limit uint64) { |
| // Disallow malloc or panic while holding the heap lock. We do |
| // this here because this is an non-mallocgc entry-point to |
| // the mheap API. |
| gp := getg() |
| gp.m.mallocing++ |
| lock(&h.lock) |
| released := h.scavengeAll(now, limit) |
| unlock(&h.lock) |
| gp.m.mallocing-- |
| |
| if debug.gctrace > 0 { |
| if released > 0 { |
| print("scvg", k, ": ", released>>20, " MB released\n") |
| } |
| print("scvg", k, ": inuse: ", memstats.heap_inuse>>20, ", idle: ", memstats.heap_idle>>20, ", sys: ", memstats.heap_sys>>20, ", released: ", memstats.heap_released>>20, ", consumed: ", (memstats.heap_sys-memstats.heap_released)>>20, " (MB)\n") |
| } |
| } |
| |
| //go:linkname runtime_debug_freeOSMemory runtime/debug.freeOSMemory |
| func runtime_debug_freeOSMemory() { |
| GC() |
| systemstack(func() { mheap_.scavenge(-1, ^uint64(0), 0) }) |
| } |
| |
| // Initialize a new span with the given start and npages. |
| func (span *mspan) init(base uintptr, npages uintptr) { |
| // span is *not* zeroed. |
| span.next = nil |
| span.prev = nil |
| span.list = nil |
| span.startAddr = base |
| span.npages = npages |
| span.allocCount = 0 |
| span.spanclass = 0 |
| span.elemsize = 0 |
| span.state = mSpanDead |
| span.unusedsince = 0 |
| span.scavenged = false |
| span.speciallock.key = 0 |
| span.specials = nil |
| span.needzero = 0 |
| span.freeindex = 0 |
| span.allocBits = nil |
| span.gcmarkBits = nil |
| } |
| |
| func (span *mspan) inList() bool { |
| return span.list != nil |
| } |
| |
| // Initialize an empty doubly-linked list. |
| func (list *mSpanList) init() { |
| list.first = nil |
| list.last = nil |
| } |
| |
| func (list *mSpanList) remove(span *mspan) { |
| if span.list != list { |
| print("runtime: failed mSpanList.remove span.npages=", span.npages, |
| " span=", span, " prev=", span.prev, " span.list=", span.list, " list=", list, "\n") |
| throw("mSpanList.remove") |
| } |
| if list.first == span { |
| list.first = span.next |
| } else { |
| span.prev.next = span.next |
| } |
| if list.last == span { |
| list.last = span.prev |
| } else { |
| span.next.prev = span.prev |
| } |
| span.next = nil |
| span.prev = nil |
| span.list = nil |
| } |
| |
| func (list *mSpanList) isEmpty() bool { |
| return list.first == nil |
| } |
| |
| func (list *mSpanList) insert(span *mspan) { |
| if span.next != nil || span.prev != nil || span.list != nil { |
| println("runtime: failed mSpanList.insert", span, span.next, span.prev, span.list) |
| throw("mSpanList.insert") |
| } |
| span.next = list.first |
| if list.first != nil { |
| // The list contains at least one span; link it in. |
| // The last span in the list doesn't change. |
| list.first.prev = span |
| } else { |
| // The list contains no spans, so this is also the last span. |
| list.last = span |
| } |
| list.first = span |
| span.list = list |
| } |
| |
| func (list *mSpanList) insertBack(span *mspan) { |
| if span.next != nil || span.prev != nil || span.list != nil { |
| println("runtime: failed mSpanList.insertBack", span, span.next, span.prev, span.list) |
| throw("mSpanList.insertBack") |
| } |
| span.prev = list.last |
| if list.last != nil { |
| // The list contains at least one span. |
| list.last.next = span |
| } else { |
| // The list contains no spans, so this is also the first span. |
| list.first = span |
| } |
| list.last = span |
| span.list = list |
| } |
| |
| // takeAll removes all spans from other and inserts them at the front |
| // of list. |
| func (list *mSpanList) takeAll(other *mSpanList) { |
| if other.isEmpty() { |
| return |
| } |
| |
| // Reparent everything in other to list. |
| for s := other.first; s != nil; s = s.next { |
| s.list = list |
| } |
| |
| // Concatenate the lists. |
| if list.isEmpty() { |
| *list = *other |
| } else { |
| // Neither list is empty. Put other before list. |
| other.last.next = list.first |
| list.first.prev = other.last |
| list.first = other.first |
| } |
| |
| other.first, other.last = nil, nil |
| } |
| |
| const ( |
| _KindSpecialFinalizer = 1 |
| _KindSpecialProfile = 2 |
| // Note: The finalizer special must be first because if we're freeing |
| // an object, a finalizer special will cause the freeing operation |
| // to abort, and we want to keep the other special records around |
| // if that happens. |
| ) |
| |
| //go:notinheap |
| type special struct { |
| next *special // linked list in span |
| offset uint16 // span offset of object |
| kind byte // kind of special |
| } |
| |
| // Adds the special record s to the list of special records for |
| // the object p. All fields of s should be filled in except for |
| // offset & next, which this routine will fill in. |
| // Returns true if the special was successfully added, false otherwise. |
| // (The add will fail only if a record with the same p and s->kind |
| // already exists.) |
| func addspecial(p unsafe.Pointer, s *special) bool { |
| span := spanOfHeap(uintptr(p)) |
| if span == nil { |
| throw("addspecial on invalid pointer") |
| } |
| |
| // Ensure that the span is swept. |
| // Sweeping accesses the specials list w/o locks, so we have |
| // to synchronize with it. And it's just much safer. |
| mp := acquirem() |
| span.ensureSwept() |
| |
| offset := uintptr(p) - span.base() |
| kind := s.kind |
| |
| lock(&span.speciallock) |
| |
| // Find splice point, check for existing record. |
| t := &span.specials |
| for { |
| x := *t |
| if x == nil { |
| break |
| } |
| if offset == uintptr(x.offset) && kind == x.kind { |
| unlock(&span.speciallock) |
| releasem(mp) |
| return false // already exists |
| } |
| if offset < uintptr(x.offset) || (offset == uintptr(x.offset) && kind < x.kind) { |
| break |
| } |
| t = &x.next |
| } |
| |
| // Splice in record, fill in offset. |
| s.offset = uint16(offset) |
| s.next = *t |
| *t = s |
| unlock(&span.speciallock) |
| releasem(mp) |
| |
| return true |
| } |
| |
| // Removes the Special record of the given kind for the object p. |
| // Returns the record if the record existed, nil otherwise. |
| // The caller must FixAlloc_Free the result. |
| func removespecial(p unsafe.Pointer, kind uint8) *special { |
| span := spanOfHeap(uintptr(p)) |
| if span == nil { |
| throw("removespecial on invalid pointer") |
| } |
| |
| // Ensure that the span is swept. |
| // Sweeping accesses the specials list w/o locks, so we have |
| // to synchronize with it. And it's just much safer. |
| mp := acquirem() |
| span.ensureSwept() |
| |
| offset := uintptr(p) - span.base() |
| |
| lock(&span.speciallock) |
| t := &span.specials |
| for { |
| s := *t |
| if s == nil { |
| break |
| } |
| // This function is used for finalizers only, so we don't check for |
| // "interior" specials (p must be exactly equal to s->offset). |
| if offset == uintptr(s.offset) && kind == s.kind { |
| *t = s.next |
| unlock(&span.speciallock) |
| releasem(mp) |
| return s |
| } |
| t = &s.next |
| } |
| unlock(&span.speciallock) |
| releasem(mp) |
| return nil |
| } |
| |
| // The described object has a finalizer set for it. |
| // |
| // specialfinalizer is allocated from non-GC'd memory, so any heap |
| // pointers must be specially handled. |
| // |
| //go:notinheap |
| type specialfinalizer struct { |
| special special |
| fn *funcval // May be a heap pointer. |
| nret uintptr |
| fint *_type // May be a heap pointer, but always live. |
| ot *ptrtype // May be a heap pointer, but always live. |
| } |
| |
| // Adds a finalizer to the object p. Returns true if it succeeded. |
| func addfinalizer(p unsafe.Pointer, f *funcval, nret uintptr, fint *_type, ot *ptrtype) bool { |
| lock(&mheap_.speciallock) |
| s := (*specialfinalizer)(mheap_.specialfinalizeralloc.alloc()) |
| unlock(&mheap_.speciallock) |
| s.special.kind = _KindSpecialFinalizer |
| s.fn = f |
| s.nret = nret |
| s.fint = fint |
| s.ot = ot |
| if addspecial(p, &s.special) { |
| // This is responsible for maintaining the same |
| // GC-related invariants as markrootSpans in any |
| // situation where it's possible that markrootSpans |
| // has already run but mark termination hasn't yet. |
| if gcphase != _GCoff { |
| base, _, _ := findObject(uintptr(p), 0, 0) |
| mp := acquirem() |
| gcw := &mp.p.ptr().gcw |
| // Mark everything reachable from the object |
| // so it's retained for the finalizer. |
| scanobject(base, gcw) |
| // Mark the finalizer itself, since the |
| // special isn't part of the GC'd heap. |
| scanblock(uintptr(unsafe.Pointer(&s.fn)), sys.PtrSize, &oneptrmask[0], gcw, nil) |
| releasem(mp) |
| } |
| return true |
| } |
| |
| // There was an old finalizer |
| lock(&mheap_.speciallock) |
| mheap_.specialfinalizeralloc.free(unsafe.Pointer(s)) |
| unlock(&mheap_.speciallock) |
| return false |
| } |
| |
| // Removes the finalizer (if any) from the object p. |
| func removefinalizer(p unsafe.Pointer) { |
| s := (*specialfinalizer)(unsafe.Pointer(removespecial(p, _KindSpecialFinalizer))) |
| if s == nil { |
| return // there wasn't a finalizer to remove |
| } |
| lock(&mheap_.speciallock) |
| mheap_.specialfinalizeralloc.free(unsafe.Pointer(s)) |
| unlock(&mheap_.speciallock) |
| } |
| |
| // The described object is being heap profiled. |
| // |
| //go:notinheap |
| type specialprofile struct { |
| special special |
| b *bucket |
| } |
| |
| // Set the heap profile bucket associated with addr to b. |
| func setprofilebucket(p unsafe.Pointer, b *bucket) { |
| lock(&mheap_.speciallock) |
| s := (*specialprofile)(mheap_.specialprofilealloc.alloc()) |
| unlock(&mheap_.speciallock) |
| s.special.kind = _KindSpecialProfile |
| s.b = b |
| if !addspecial(p, &s.special) { |
| throw("setprofilebucket: profile already set") |
| } |
| } |
| |
| // Do whatever cleanup needs to be done to deallocate s. It has |
| // already been unlinked from the mspan specials list. |
| func freespecial(s *special, p unsafe.Pointer, size uintptr) { |
| switch s.kind { |
| case _KindSpecialFinalizer: |
| sf := (*specialfinalizer)(unsafe.Pointer(s)) |
| queuefinalizer(p, sf.fn, sf.nret, sf.fint, sf.ot) |
| lock(&mheap_.speciallock) |
| mheap_.specialfinalizeralloc.free(unsafe.Pointer(sf)) |
| unlock(&mheap_.speciallock) |
| case _KindSpecialProfile: |
| sp := (*specialprofile)(unsafe.Pointer(s)) |
| mProf_Free(sp.b, size) |
| lock(&mheap_.speciallock) |
| mheap_.specialprofilealloc.free(unsafe.Pointer(sp)) |
| unlock(&mheap_.speciallock) |
| default: |
| throw("bad special kind") |
| panic("not reached") |
| } |
| } |
| |
| // gcBits is an alloc/mark bitmap. This is always used as *gcBits. |
| // |
| //go:notinheap |
| type gcBits uint8 |
| |
| // bytep returns a pointer to the n'th byte of b. |
| func (b *gcBits) bytep(n uintptr) *uint8 { |
| return addb((*uint8)(b), n) |
| } |
| |
| // bitp returns a pointer to the byte containing bit n and a mask for |
| // selecting that bit from *bytep. |
| func (b *gcBits) bitp(n uintptr) (bytep *uint8, mask uint8) { |
| return b.bytep(n / 8), 1 << (n % 8) |
| } |
| |
| const gcBitsChunkBytes = uintptr(64 << 10) |
| const gcBitsHeaderBytes = unsafe.Sizeof(gcBitsHeader{}) |
| |
| type gcBitsHeader struct { |
| free uintptr // free is the index into bits of the next free byte. |
| next uintptr // *gcBits triggers recursive type bug. (issue 14620) |
| } |
| |
| //go:notinheap |
| type gcBitsArena struct { |
| // gcBitsHeader // side step recursive type bug (issue 14620) by including fields by hand. |
| free uintptr // free is the index into bits of the next free byte; read/write atomically |
| next *gcBitsArena |
| bits [gcBitsChunkBytes - gcBitsHeaderBytes]gcBits |
| } |
| |
| var gcBitsArenas struct { |
| lock mutex |
| free *gcBitsArena |
| next *gcBitsArena // Read atomically. Write atomically under lock. |
| current *gcBitsArena |
| previous *gcBitsArena |
| } |
| |
| // tryAlloc allocates from b or returns nil if b does not have enough room. |
| // This is safe to call concurrently. |
| func (b *gcBitsArena) tryAlloc(bytes uintptr) *gcBits { |
| if b == nil || atomic.Loaduintptr(&b.free)+bytes > uintptr(len(b.bits)) { |
| return nil |
| } |
| // Try to allocate from this block. |
| end := atomic.Xadduintptr(&b.free, bytes) |
| if end > uintptr(len(b.bits)) { |
| return nil |
| } |
| // There was enough room. |
| start := end - bytes |
| return &b.bits[start] |
| } |
| |
| // newMarkBits returns a pointer to 8 byte aligned bytes |
| // to be used for a span's mark bits. |
| func newMarkBits(nelems uintptr) *gcBits { |
| blocksNeeded := uintptr((nelems + 63) / 64) |
| bytesNeeded := blocksNeeded * 8 |
| |
| // Try directly allocating from the current head arena. |
| head := (*gcBitsArena)(atomic.Loadp(unsafe.Pointer(&gcBitsArenas.next))) |
| if p := head.tryAlloc(bytesNeeded); p != nil { |
| return p |
| } |
| |
| // There's not enough room in the head arena. We may need to |
| // allocate a new arena. |
| lock(&gcBitsArenas.lock) |
| // Try the head arena again, since it may have changed. Now |
| // that we hold the lock, the list head can't change, but its |
| // free position still can. |
| if p := gcBitsArenas.next.tryAlloc(bytesNeeded); p != nil { |
| unlock(&gcBitsArenas.lock) |
| return p |
| } |
| |
| // Allocate a new arena. This may temporarily drop the lock. |
| fresh := newArenaMayUnlock() |
| // If newArenaMayUnlock dropped the lock, another thread may |
| // have put a fresh arena on the "next" list. Try allocating |
| // from next again. |
| if p := gcBitsArenas.next.tryAlloc(bytesNeeded); p != nil { |
| // Put fresh back on the free list. |
| // TODO: Mark it "already zeroed" |
| fresh.next = gcBitsArenas.free |
| gcBitsArenas.free = fresh |
| unlock(&gcBitsArenas.lock) |
| return p |
| } |
| |
| // Allocate from the fresh arena. We haven't linked it in yet, so |
| // this cannot race and is guaranteed to succeed. |
| p := fresh.tryAlloc(bytesNeeded) |
| if p == nil { |
| throw("markBits overflow") |
| } |
| |
| // Add the fresh arena to the "next" list. |
| fresh.next = gcBitsArenas.next |
| atomic.StorepNoWB(unsafe.Pointer(&gcBitsArenas.next), unsafe.Pointer(fresh)) |
| |
| unlock(&gcBitsArenas.lock) |
| return p |
| } |
| |
| // newAllocBits returns a pointer to 8 byte aligned bytes |
| // to be used for this span's alloc bits. |
| // newAllocBits is used to provide newly initialized spans |
| // allocation bits. For spans not being initialized the |
| // mark bits are repurposed as allocation bits when |
| // the span is swept. |
| func newAllocBits(nelems uintptr) *gcBits { |
| return newMarkBits(nelems) |
| } |
| |
| // nextMarkBitArenaEpoch establishes a new epoch for the arenas |
| // holding the mark bits. The arenas are named relative to the |
| // current GC cycle which is demarcated by the call to finishweep_m. |
| // |
| // All current spans have been swept. |
| // During that sweep each span allocated room for its gcmarkBits in |
| // gcBitsArenas.next block. gcBitsArenas.next becomes the gcBitsArenas.current |
| // where the GC will mark objects and after each span is swept these bits |
| // will be used to allocate objects. |
| // gcBitsArenas.current becomes gcBitsArenas.previous where the span's |
| // gcAllocBits live until all the spans have been swept during this GC cycle. |
| // The span's sweep extinguishes all the references to gcBitsArenas.previous |
| // by pointing gcAllocBits into the gcBitsArenas.current. |
| // The gcBitsArenas.previous is released to the gcBitsArenas.free list. |
| func nextMarkBitArenaEpoch() { |
| lock(&gcBitsArenas.lock) |
| if gcBitsArenas.previous != nil { |
| if gcBitsArenas.free == nil { |
| gcBitsArenas.free = gcBitsArenas.previous |
| } else { |
| // Find end of previous arenas. |
| last := gcBitsArenas.previous |
| for last = gcBitsArenas.previous; last.next != nil; last = last.next { |
| } |
| last.next = gcBitsArenas.free |
| gcBitsArenas.free = gcBitsArenas.previous |
| } |
| } |
| gcBitsArenas.previous = gcBitsArenas.current |
| gcBitsArenas.current = gcBitsArenas.next |
| atomic.StorepNoWB(unsafe.Pointer(&gcBitsArenas.next), nil) // newMarkBits calls newArena when needed |
| unlock(&gcBitsArenas.lock) |
| } |
| |
| // newArenaMayUnlock allocates and zeroes a gcBits arena. |
| // The caller must hold gcBitsArena.lock. This may temporarily release it. |
| func newArenaMayUnlock() *gcBitsArena { |
| var result *gcBitsArena |
| if gcBitsArenas.free == nil { |
| unlock(&gcBitsArenas.lock) |
| result = (*gcBitsArena)(sysAlloc(gcBitsChunkBytes, &memstats.gc_sys)) |
| if result == nil { |
| throw("runtime: cannot allocate memory") |
| } |
| lock(&gcBitsArenas.lock) |
| } else { |
| result = gcBitsArenas.free |
| gcBitsArenas.free = gcBitsArenas.free.next |
| memclrNoHeapPointers(unsafe.Pointer(result), gcBitsChunkBytes) |
| } |
| result.next = nil |
| // If result.bits is not 8 byte aligned adjust index so |
| // that &result.bits[result.free] is 8 byte aligned. |
| if uintptr(unsafe.Offsetof(gcBitsArena{}.bits))&7 == 0 { |
| result.free = 0 |
| } else { |
| result.free = 8 - (uintptr(unsafe.Pointer(&result.bits[0])) & 7) |
| } |
| return result |
| } |