| // Copyright 2014 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 allocator. |
| // |
| // This was originally based on tcmalloc, but has diverged quite a bit. |
| // http://goog-perftools.sourceforge.net/doc/tcmalloc.html |
| |
| // The main allocator works in runs of pages. |
| // Small allocation sizes (up to and including 32 kB) are |
| // rounded to one of about 70 size classes, each of which |
| // has its own free set of objects of exactly that size. |
| // Any free page of memory can be split into a set of objects |
| // of one size class, which are then managed using a free bitmap. |
| // |
| // The allocator's data structures are: |
| // |
| // fixalloc: a free-list allocator for fixed-size off-heap objects, |
| // used to manage storage used by the allocator. |
| // mheap: the malloc heap, managed at page (8192-byte) granularity. |
| // mspan: a run of pages managed by the mheap. |
| // mcentral: collects all spans of a given size class. |
| // mcache: a per-P cache of mspans with free space. |
| // mstats: allocation statistics. |
| // |
| // Allocating a small object proceeds up a hierarchy of caches: |
| // |
| // 1. Round the size up to one of the small size classes |
| // and look in the corresponding mspan in this P's mcache. |
| // Scan the mspan's free bitmap to find a free slot. |
| // If there is a free slot, allocate it. |
| // This can all be done without acquiring a lock. |
| // |
| // 2. If the mspan has no free slots, obtain a new mspan |
| // from the mcentral's list of mspans of the required size |
| // class that have free space. |
| // Obtaining a whole span amortizes the cost of locking |
| // the mcentral. |
| // |
| // 3. If the mcentral's mspan list is empty, obtain a run |
| // of pages from the mheap to use for the mspan. |
| // |
| // 4. If the mheap is empty or has no page runs large enough, |
| // allocate a new group of pages (at least 1MB) from the |
| // operating system. Allocating a large run of pages |
| // amortizes the cost of talking to the operating system. |
| // |
| // Sweeping an mspan and freeing objects on it proceeds up a similar |
| // hierarchy: |
| // |
| // 1. If the mspan is being swept in response to allocation, it |
| // is returned to the mcache to satisfy the allocation. |
| // |
| // 2. Otherwise, if the mspan still has allocated objects in it, |
| // it is placed on the mcentral free list for the mspan's size |
| // class. |
| // |
| // 3. Otherwise, if all objects in the mspan are free, the mspan |
| // is now "idle", so it is returned to the mheap and no longer |
| // has a size class. |
| // This may coalesce it with adjacent idle mspans. |
| // |
| // 4. If an mspan remains idle for long enough, return its pages |
| // to the operating system. |
| // |
| // Allocating and freeing a large object uses the mheap |
| // directly, bypassing the mcache and mcentral. |
| // |
| // Free object slots in an mspan are zeroed only if mspan.needzero is |
| // false. If needzero is true, objects are zeroed as they are |
| // allocated. There are various benefits to delaying zeroing this way: |
| // |
| // 1. Stack frame allocation can avoid zeroing altogether. |
| // |
| // 2. It exhibits better temporal locality, since the program is |
| // probably about to write to the memory. |
| // |
| // 3. We don't zero pages that never get reused. |
| |
| // Virtual memory layout |
| // |
| // The heap consists of a set of arenas, which are 64MB on 64-bit and |
| // 4MB on 32-bit (heapArenaBytes). Each arena's start address is also |
| // aligned to the arena size. |
| // |
| // Each arena has an associated heapArena object that stores the |
| // metadata for that arena: the heap bitmap for all words in the arena |
| // and the span map for all pages in the arena. heapArena objects are |
| // themselves allocated off-heap. |
| // |
| // Since arenas are aligned, the address space can be viewed as a |
| // series of arena frames. The arena map (mheap_.arenas) maps from |
| // arena frame number to *heapArena, or nil for parts of the address |
| // space not backed by the Go heap. The arena map is structured as a |
| // two-level array consisting of a "L1" arena map and many "L2" arena |
| // maps; however, since arenas are large, on many architectures, the |
| // arena map consists of a single, large L2 map. |
| // |
| // The arena map covers the entire possible address space, allowing |
| // the Go heap to use any part of the address space. The allocator |
| // attempts to keep arenas contiguous so that large spans (and hence |
| // large objects) can cross arenas. |
| |
| package runtime |
| |
| import ( |
| "runtime/internal/atomic" |
| "runtime/internal/sys" |
| "unsafe" |
| ) |
| |
| const ( |
| debugMalloc = false |
| |
| maxTinySize = _TinySize |
| tinySizeClass = _TinySizeClass |
| maxSmallSize = _MaxSmallSize |
| |
| pageShift = _PageShift |
| pageSize = _PageSize |
| pageMask = _PageMask |
| // By construction, single page spans of the smallest object class |
| // have the most objects per span. |
| maxObjsPerSpan = pageSize / 8 |
| |
| mSpanInUse = _MSpanInUse |
| |
| concurrentSweep = _ConcurrentSweep |
| |
| _PageSize = 1 << _PageShift |
| _PageMask = _PageSize - 1 |
| |
| // _64bit = 1 on 64-bit systems, 0 on 32-bit systems |
| _64bit = 1 << (^uintptr(0) >> 63) / 2 |
| |
| // Tiny allocator parameters, see "Tiny allocator" comment in malloc.go. |
| _TinySize = 16 |
| _TinySizeClass = int8(2) |
| |
| _FixAllocChunk = 16 << 10 // Chunk size for FixAlloc |
| _MaxMHeapList = 1 << (20 - _PageShift) // Maximum page length for fixed-size list in MHeap. |
| |
| // Per-P, per order stack segment cache size. |
| _StackCacheSize = 32 * 1024 |
| |
| // Number of orders that get caching. Order 0 is FixedStack |
| // and each successive order is twice as large. |
| // We want to cache 2KB, 4KB, 8KB, and 16KB stacks. Larger stacks |
| // will be allocated directly. |
| // Since FixedStack is different on different systems, we |
| // must vary NumStackOrders to keep the same maximum cached size. |
| // OS | FixedStack | NumStackOrders |
| // -----------------+------------+--------------- |
| // linux/darwin/bsd | 2KB | 4 |
| // windows/32 | 4KB | 3 |
| // windows/64 | 8KB | 2 |
| // plan9 | 4KB | 3 |
| _NumStackOrders = 4 - sys.PtrSize/4*sys.GoosWindows - 1*sys.GoosPlan9 |
| |
| // heapAddrBits is the number of bits in a heap address. On |
| // amd64, addresses are sign-extended beyond heapAddrBits. On |
| // other arches, they are zero-extended. |
| // |
| // On 64-bit platforms, we limit this to 48 bits based on a |
| // combination of hardware and OS limitations. |
| // |
| // amd64 hardware limits addresses to 48 bits, sign-extended |
| // to 64 bits. Addresses where the top 16 bits are not either |
| // all 0 or all 1 are "non-canonical" and invalid. Because of |
| // these "negative" addresses, we offset addresses by 1<<47 |
| // (arenaBaseOffset) on amd64 before computing indexes into |
| // the heap arenas index. In 2017, amd64 hardware added |
| // support for 57 bit addresses; however, currently only Linux |
| // supports this extension and the kernel will never choose an |
| // address above 1<<47 unless mmap is called with a hint |
| // address above 1<<47 (which we never do). |
| // |
| // arm64 hardware (as of ARMv8) limits user addresses to 48 |
| // bits, in the range [0, 1<<48). |
| // |
| // ppc64, mips64, and s390x support arbitrary 64 bit addresses |
| // in hardware. However, since Go only supports Linux on |
| // these, we lean on OS limits. Based on Linux's processor.h, |
| // the user address space is limited as follows on 64-bit |
| // architectures: |
| // |
| // Architecture Name Maximum Value (exclusive) |
| // --------------------------------------------------------------------- |
| // amd64 TASK_SIZE_MAX 0x007ffffffff000 (47 bit addresses) |
| // arm64 TASK_SIZE_64 0x01000000000000 (48 bit addresses) |
| // ppc64{,le} TASK_SIZE_USER64 0x00400000000000 (46 bit addresses) |
| // mips64{,le} TASK_SIZE64 0x00010000000000 (40 bit addresses) |
| // s390x TASK_SIZE 1<<64 (64 bit addresses) |
| // |
| // These limits may increase over time, but are currently at |
| // most 48 bits except on s390x. On all architectures, Linux |
| // starts placing mmap'd regions at addresses that are |
| // significantly below 48 bits, so even if it's possible to |
| // exceed Go's 48 bit limit, it's extremely unlikely in |
| // practice. |
| // |
| // On 32-bit platforms, we accept the full 32-bit address |
| // space because doing so is cheap. |
| // mips32 only has access to the low 2GB of virtual memory, so |
| // we further limit it to 31 bits. |
| heapAddrBits = _64bit*48 + (1-_64bit)*(32-(sys.GoarchMips+sys.GoarchMipsle)) |
| |
| // maxAlloc is the maximum size of an allocation. On 64-bit, |
| // it's theoretically possible to allocate 1<<heapAddrBits bytes. On |
| // 32-bit, however, this is one less than 1<<32 because the |
| // number of bytes in the address space doesn't actually fit |
| // in a uintptr. |
| maxAlloc = (1 << heapAddrBits) - (1-_64bit)*1 |
| |
| // The number of bits in a heap address, the size of heap |
| // arenas, and the L1 and L2 arena map sizes are related by |
| // |
| // (1 << addrBits) = arenaBytes * L1entries * L2entries |
| // |
| // Currently, we balance these as follows: |
| // |
| // Platform Addr bits Arena size L1 entries L2 size |
| // -------------- --------- ---------- ---------- ------- |
| // */64-bit 48 64MB 1 32MB |
| // windows/64-bit 48 4MB 64 8MB |
| // */32-bit 32 4MB 1 4KB |
| // */mips(le) 31 4MB 1 2KB |
| |
| // heapArenaBytes is the size of a heap arena. The heap |
| // consists of mappings of size heapArenaBytes, aligned to |
| // heapArenaBytes. The initial heap mapping is one arena. |
| // |
| // This is currently 64MB on 64-bit non-Windows and 4MB on |
| // 32-bit and on Windows. We use smaller arenas on Windows |
| // because all committed memory is charged to the process, |
| // even if it's not touched. Hence, for processes with small |
| // heaps, the mapped arena space needs to be commensurate. |
| // This is particularly important with the race detector, |
| // since it significantly amplifies the cost of committed |
| // memory. |
| heapArenaBytes = 1 << logHeapArenaBytes |
| |
| // logHeapArenaBytes is log_2 of heapArenaBytes. For clarity, |
| // prefer using heapArenaBytes where possible (we need the |
| // constant to compute some other constants). |
| logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) |
| |
| // heapArenaBitmapBytes is the size of each heap arena's bitmap. |
| heapArenaBitmapBytes = heapArenaBytes / (sys.PtrSize * 8 / 2) |
| |
| pagesPerArena = heapArenaBytes / pageSize |
| |
| // arenaL1Bits is the number of bits of the arena number |
| // covered by the first level arena map. |
| // |
| // This number should be small, since the first level arena |
| // map requires PtrSize*(1<<arenaL1Bits) of space in the |
| // binary's BSS. It can be zero, in which case the first level |
| // index is effectively unused. There is a performance benefit |
| // to this, since the generated code can be more efficient, |
| // but comes at the cost of having a large L2 mapping. |
| // |
| // We use the L1 map on 64-bit Windows because the arena size |
| // is small, but the address space is still 48 bits, and |
| // there's a high cost to having a large L2. |
| arenaL1Bits = 6 * (_64bit * sys.GoosWindows) |
| |
| // arenaL2Bits is the number of bits of the arena number |
| // covered by the second level arena index. |
| // |
| // The size of each arena map allocation is proportional to |
| // 1<<arenaL2Bits, so it's important that this not be too |
| // large. 48 bits leads to 32MB arena index allocations, which |
| // is about the practical threshold. |
| arenaL2Bits = heapAddrBits - logHeapArenaBytes - arenaL1Bits |
| |
| // arenaL1Shift is the number of bits to shift an arena frame |
| // number by to compute an index into the first level arena map. |
| arenaL1Shift = arenaL2Bits |
| |
| // arenaBits is the total bits in a combined arena map index. |
| // This is split between the index into the L1 arena map and |
| // the L2 arena map. |
| arenaBits = arenaL1Bits + arenaL2Bits |
| |
| // arenaBaseOffset is the pointer value that corresponds to |
| // index 0 in the heap arena map. |
| // |
| // On amd64, the address space is 48 bits, sign extended to 64 |
| // bits. This offset lets us handle "negative" addresses (or |
| // high addresses if viewed as unsigned). |
| // |
| // On other platforms, the user address space is contiguous |
| // and starts at 0, so no offset is necessary. |
| arenaBaseOffset uintptr = sys.GoarchAmd64 * (1 << 47) |
| |
| // Max number of threads to run garbage collection. |
| // 2, 3, and 4 are all plausible maximums depending |
| // on the hardware details of the machine. The garbage |
| // collector scales well to 32 cpus. |
| _MaxGcproc = 32 |
| |
| // minLegalPointer is the smallest possible legal pointer. |
| // This is the smallest possible architectural page size, |
| // since we assume that the first page is never mapped. |
| // |
| // This should agree with minZeroPage in the compiler. |
| minLegalPointer uintptr = 4096 |
| ) |
| |
| // physPageSize is the size in bytes of the OS's physical pages. |
| // Mapping and unmapping operations must be done at multiples of |
| // physPageSize. |
| // |
| // This must be set by the OS init code (typically in osinit) before |
| // mallocinit. |
| var physPageSize uintptr |
| |
| // OS-defined helpers: |
| // |
| // sysAlloc obtains a large chunk of zeroed memory from the |
| // operating system, typically on the order of a hundred kilobytes |
| // or a megabyte. |
| // NOTE: sysAlloc returns OS-aligned memory, but the heap allocator |
| // may use larger alignment, so the caller must be careful to realign the |
| // memory obtained by sysAlloc. |
| // |
| // SysUnused notifies the operating system that the contents |
| // of the memory region are no longer needed and can be reused |
| // for other purposes. |
| // SysUsed notifies the operating system that the contents |
| // of the memory region are needed again. |
| // |
| // SysFree returns it unconditionally; this is only used if |
| // an out-of-memory error has been detected midway through |
| // an allocation. It is okay if SysFree is a no-op. |
| // |
| // SysReserve reserves address space without allocating memory. |
| // If the pointer passed to it is non-nil, the caller wants the |
| // reservation there, but SysReserve can still choose another |
| // location if that one is unavailable. |
| // NOTE: SysReserve returns OS-aligned memory, but the heap allocator |
| // may use larger alignment, so the caller must be careful to realign the |
| // memory obtained by sysAlloc. |
| // |
| // SysMap maps previously reserved address space for use. |
| // |
| // SysFault marks a (already sysAlloc'd) region to fault |
| // if accessed. Used only for debugging the runtime. |
| |
| func mallocinit() { |
| if class_to_size[_TinySizeClass] != _TinySize { |
| throw("bad TinySizeClass") |
| } |
| |
| testdefersizes() |
| |
| if heapArenaBitmapBytes&(heapArenaBitmapBytes-1) != 0 { |
| // heapBits expects modular arithmetic on bitmap |
| // addresses to work. |
| throw("heapArenaBitmapBytes not a power of 2") |
| } |
| |
| // Copy class sizes out for statistics table. |
| for i := range class_to_size { |
| memstats.by_size[i].size = uint32(class_to_size[i]) |
| } |
| |
| // Check physPageSize. |
| if physPageSize == 0 { |
| // The OS init code failed to fetch the physical page size. |
| throw("failed to get system page size") |
| } |
| if physPageSize < minPhysPageSize { |
| print("system page size (", physPageSize, ") is smaller than minimum page size (", minPhysPageSize, ")\n") |
| throw("bad system page size") |
| } |
| if physPageSize&(physPageSize-1) != 0 { |
| print("system page size (", physPageSize, ") must be a power of 2\n") |
| throw("bad system page size") |
| } |
| |
| // Initialize the heap. |
| mheap_.init() |
| _g_ := getg() |
| _g_.m.mcache = allocmcache() |
| |
| // Create initial arena growth hints. |
| if sys.PtrSize == 8 { |
| // On a 64-bit machine, we pick the following hints |
| // because: |
| // |
| // 1. Starting from the middle of the address space |
| // makes it easier to grow out a contiguous range |
| // without running in to some other mapping. |
| // |
| // 2. This makes Go heap addresses more easily |
| // recognizable when debugging. |
| // |
| // 3. Stack scanning in gccgo is still conservative, |
| // so it's important that addresses be distinguishable |
| // from other data. |
| // |
| // Starting at 0x00c0 means that the valid memory addresses |
| // will begin 0x00c0, 0x00c1, ... |
| // In little-endian, that's c0 00, c1 00, ... None of those are valid |
| // UTF-8 sequences, and they are otherwise as far away from |
| // ff (likely a common byte) as possible. If that fails, we try other 0xXXc0 |
| // addresses. An earlier attempt to use 0x11f8 caused out of memory errors |
| // on OS X during thread allocations. 0x00c0 causes conflicts with |
| // AddressSanitizer which reserves all memory up to 0x0100. |
| // These choices reduce the odds of a conservative garbage collector |
| // not collecting memory because some non-pointer block of memory |
| // had a bit pattern that matched a memory address. |
| // |
| // However, on arm64, we ignore all this advice above and slam the |
| // allocation at 0x40 << 32 because when using 4k pages with 3-level |
| // translation buffers, the user address space is limited to 39 bits |
| // On darwin/arm64, the address space is even smaller. |
| for i := 0x7f; i >= 0; i-- { |
| var p uintptr |
| switch { |
| case GOARCH == "arm64" && GOOS == "darwin": |
| p = uintptr(i)<<40 | uintptrMask&(0x0013<<28) |
| case GOARCH == "arm64": |
| p = uintptr(i)<<40 | uintptrMask&(0x0040<<32) |
| default: |
| p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32) |
| } |
| hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc()) |
| hint.addr = p |
| hint.next, mheap_.arenaHints = mheap_.arenaHints, hint |
| } |
| } else { |
| // On a 32-bit machine, we're much more concerned |
| // about keeping the usable heap contiguous. |
| // Hence: |
| // |
| // 1. We reserve space for all heapArenas up front so |
| // they don't get interleaved with the heap. They're |
| // ~258MB, so this isn't too bad. (We could reserve a |
| // smaller amount of space up front if this is a |
| // problem.) |
| // |
| // 2. We hint the heap to start right above the end of |
| // the binary so we have the best chance of keeping it |
| // contiguous. |
| // |
| // 3. We try to stake out a reasonably large initial |
| // heap reservation. |
| |
| const arenaMetaSize = unsafe.Sizeof([1 << arenaBits]heapArena{}) |
| meta := uintptr(sysReserve(nil, arenaMetaSize)) |
| if meta != 0 { |
| mheap_.heapArenaAlloc.init(meta, arenaMetaSize) |
| } |
| |
| // We want to start the arena low, but if we're linked |
| // against C code, it's possible global constructors |
| // have called malloc and adjusted the process' brk. |
| // Query the brk so we can avoid trying to map the |
| // region over it (which will cause the kernel to put |
| // the region somewhere else, likely at a high |
| // address). |
| procBrk := sbrk0() |
| |
| // If we ask for the end of the data segment but the |
| // operating system requires a little more space |
| // before we can start allocating, it will give out a |
| // slightly higher pointer. Except QEMU, which is |
| // buggy, as usual: it won't adjust the pointer |
| // upward. So adjust it upward a little bit ourselves: |
| // 1/4 MB to get away from the running binary image. |
| p := firstmoduledata.end |
| if p < procBrk { |
| p = procBrk |
| } |
| if mheap_.heapArenaAlloc.next <= p && p < mheap_.heapArenaAlloc.end { |
| p = mheap_.heapArenaAlloc.end |
| } |
| p = round(p+(256<<10), heapArenaBytes) |
| // Because we're worried about fragmentation on |
| // 32-bit, we try to make a large initial reservation. |
| arenaSizes := []uintptr{ |
| 512 << 20, |
| 256 << 20, |
| 128 << 20, |
| } |
| for _, arenaSize := range arenaSizes { |
| a, size := sysReserveAligned(unsafe.Pointer(p), arenaSize, heapArenaBytes) |
| if a != nil { |
| mheap_.arena.init(uintptr(a), size) |
| p = uintptr(a) + size // For hint below |
| break |
| } |
| } |
| hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc()) |
| hint.addr = p |
| hint.next, mheap_.arenaHints = mheap_.arenaHints, hint |
| } |
| } |
| |
| // sysAlloc allocates heap arena space for at least n bytes. The |
| // returned pointer is always heapArenaBytes-aligned and backed by |
| // h.arenas metadata. The returned size is always a multiple of |
| // heapArenaBytes. sysAlloc returns nil on failure. |
| // There is no corresponding free function. |
| // |
| // h must be locked. |
| func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) { |
| n = round(n, heapArenaBytes) |
| |
| // First, try the arena pre-reservation. |
| v = h.arena.alloc(n, heapArenaBytes, &memstats.heap_sys) |
| if v != nil { |
| size = n |
| goto mapped |
| } |
| |
| // Try to grow the heap at a hint address. |
| for h.arenaHints != nil { |
| hint := h.arenaHints |
| p := hint.addr |
| if hint.down { |
| p -= n |
| } |
| if p+n < p { |
| // We can't use this, so don't ask. |
| v = nil |
| } else if arenaIndex(p+n-1) >= 1<<arenaBits { |
| // Outside addressable heap. Can't use. |
| v = nil |
| } else { |
| v = sysReserve(unsafe.Pointer(p), n) |
| } |
| if p == uintptr(v) { |
| // Success. Update the hint. |
| if !hint.down { |
| p += n |
| } |
| hint.addr = p |
| size = n |
| break |
| } |
| // Failed. Discard this hint and try the next. |
| // |
| // TODO: This would be cleaner if sysReserve could be |
| // told to only return the requested address. In |
| // particular, this is already how Windows behaves, so |
| // it would simply things there. |
| if v != nil { |
| sysFree(v, n, nil) |
| } |
| h.arenaHints = hint.next |
| h.arenaHintAlloc.free(unsafe.Pointer(hint)) |
| } |
| |
| if size == 0 { |
| if raceenabled { |
| // The race detector assumes the heap lives in |
| // [0x00c000000000, 0x00e000000000), but we |
| // just ran out of hints in this region. Give |
| // a nice failure. |
| throw("too many address space collisions for -race mode") |
| } |
| |
| // All of the hints failed, so we'll take any |
| // (sufficiently aligned) address the kernel will give |
| // us. |
| v, size = sysReserveAligned(nil, n, heapArenaBytes) |
| if v == nil { |
| return nil, 0 |
| } |
| |
| // Create new hints for extending this region. |
| hint := (*arenaHint)(h.arenaHintAlloc.alloc()) |
| hint.addr, hint.down = uintptr(v), true |
| hint.next, mheap_.arenaHints = mheap_.arenaHints, hint |
| hint = (*arenaHint)(h.arenaHintAlloc.alloc()) |
| hint.addr = uintptr(v) + size |
| hint.next, mheap_.arenaHints = mheap_.arenaHints, hint |
| } |
| |
| // Check for bad pointers or pointers we can't use. |
| { |
| var bad string |
| p := uintptr(v) |
| if p+size < p { |
| bad = "region exceeds uintptr range" |
| } else if arenaIndex(p) >= 1<<arenaBits { |
| bad = "base outside usable address space" |
| } else if arenaIndex(p+size-1) >= 1<<arenaBits { |
| bad = "end outside usable address space" |
| } |
| if bad != "" { |
| // This should be impossible on most architectures, |
| // but it would be really confusing to debug. |
| print("runtime: memory allocated by OS [", hex(p), ", ", hex(p+size), ") not in usable address space: ", bad, "\n") |
| throw("memory reservation exceeds address space limit") |
| } |
| } |
| |
| if uintptr(v)&(heapArenaBytes-1) != 0 { |
| throw("misrounded allocation in sysAlloc") |
| } |
| |
| // Back the reservation. |
| sysMap(v, size, &memstats.heap_sys) |
| |
| mapped: |
| // Create arena metadata. |
| for ri := arenaIndex(uintptr(v)); ri <= arenaIndex(uintptr(v)+size-1); ri++ { |
| l2 := h.arenas[ri.l1()] |
| if l2 == nil { |
| // Allocate an L2 arena map. |
| l2 = (*[1 << arenaL2Bits]*heapArena)(persistentalloc(unsafe.Sizeof(*l2), sys.PtrSize, nil)) |
| if l2 == nil { |
| throw("out of memory allocating heap arena map") |
| } |
| atomic.StorepNoWB(unsafe.Pointer(&h.arenas[ri.l1()]), unsafe.Pointer(l2)) |
| } |
| |
| if l2[ri.l2()] != nil { |
| throw("arena already initialized") |
| } |
| var r *heapArena |
| r = (*heapArena)(h.heapArenaAlloc.alloc(unsafe.Sizeof(*r), sys.PtrSize, &memstats.gc_sys)) |
| if r == nil { |
| r = (*heapArena)(persistentalloc(unsafe.Sizeof(*r), sys.PtrSize, &memstats.gc_sys)) |
| if r == nil { |
| throw("out of memory allocating heap arena metadata") |
| } |
| } |
| |
| // Store atomically just in case an object from the |
| // new heap arena becomes visible before the heap lock |
| // is released (which shouldn't happen, but there's |
| // little downside to this). |
| atomic.StorepNoWB(unsafe.Pointer(&l2[ri.l2()]), unsafe.Pointer(r)) |
| } |
| |
| // Tell the race detector about the new heap memory. |
| if raceenabled { |
| racemapshadow(v, size) |
| } |
| |
| return |
| } |
| |
| // sysReserveAligned is like sysReserve, but the returned pointer is |
| // aligned to align bytes. It may reserve either n or n+align bytes, |
| // so it returns the size that was reserved. |
| func sysReserveAligned(v unsafe.Pointer, size, align uintptr) (unsafe.Pointer, uintptr) { |
| // Since the alignment is rather large in uses of this |
| // function, we're not likely to get it by chance, so we ask |
| // for a larger region and remove the parts we don't need. |
| retries := 0 |
| retry: |
| p := uintptr(sysReserve(v, size+align)) |
| switch { |
| case p == 0: |
| return nil, 0 |
| case p&(align-1) == 0: |
| // We got lucky and got an aligned region, so we can |
| // use the whole thing. |
| return unsafe.Pointer(p), size + align |
| case GOOS == "windows": |
| // On Windows we can't release pieces of a |
| // reservation, so we release the whole thing and |
| // re-reserve the aligned sub-region. This may race, |
| // so we may have to try again. |
| sysFree(unsafe.Pointer(p), size+align, nil) |
| p = round(p, align) |
| p2 := sysReserve(unsafe.Pointer(p), size) |
| if p != uintptr(p2) { |
| // Must have raced. Try again. |
| sysFree(p2, size, nil) |
| if retries++; retries == 100 { |
| throw("failed to allocate aligned heap memory; too many retries") |
| } |
| goto retry |
| } |
| // Success. |
| return p2, size |
| default: |
| // Trim off the unaligned parts. |
| pAligned := round(p, align) |
| sysFree(unsafe.Pointer(p), pAligned-p, nil) |
| end := pAligned + size |
| endLen := (p + size + align) - end |
| if endLen > 0 { |
| sysFree(unsafe.Pointer(end), endLen, nil) |
| } |
| return unsafe.Pointer(pAligned), size |
| } |
| } |
| |
| // base address for all 0-byte allocations |
| var zerobase uintptr |
| |
| // nextFreeFast returns the next free object if one is quickly available. |
| // Otherwise it returns 0. |
| func nextFreeFast(s *mspan) gclinkptr { |
| theBit := sys.Ctz64(s.allocCache) // Is there a free object in the allocCache? |
| if theBit < 64 { |
| result := s.freeindex + uintptr(theBit) |
| if result < s.nelems { |
| freeidx := result + 1 |
| if freeidx%64 == 0 && freeidx != s.nelems { |
| return 0 |
| } |
| s.allocCache >>= uint(theBit + 1) |
| s.freeindex = freeidx |
| s.allocCount++ |
| return gclinkptr(result*s.elemsize + s.base()) |
| } |
| } |
| return 0 |
| } |
| |
| // nextFree returns the next free object from the cached span if one is available. |
| // Otherwise it refills the cache with a span with an available object and |
| // returns that object along with a flag indicating that this was a heavy |
| // weight allocation. If it is a heavy weight allocation the caller must |
| // determine whether a new GC cycle needs to be started or if the GC is active |
| // whether this goroutine needs to assist the GC. |
| func (c *mcache) nextFree(spc spanClass) (v gclinkptr, s *mspan, shouldhelpgc bool) { |
| s = c.alloc[spc] |
| shouldhelpgc = false |
| freeIndex := s.nextFreeIndex() |
| if freeIndex == s.nelems { |
| // The span is full. |
| if uintptr(s.allocCount) != s.nelems { |
| println("runtime: s.allocCount=", s.allocCount, "s.nelems=", s.nelems) |
| throw("s.allocCount != s.nelems && freeIndex == s.nelems") |
| } |
| systemstack(func() { |
| c.refill(spc) |
| }) |
| shouldhelpgc = true |
| s = c.alloc[spc] |
| |
| freeIndex = s.nextFreeIndex() |
| } |
| |
| if freeIndex >= s.nelems { |
| throw("freeIndex is not valid") |
| } |
| |
| v = gclinkptr(freeIndex*s.elemsize + s.base()) |
| s.allocCount++ |
| if uintptr(s.allocCount) > s.nelems { |
| println("s.allocCount=", s.allocCount, "s.nelems=", s.nelems) |
| throw("s.allocCount > s.nelems") |
| } |
| return |
| } |
| |
| // Allocate an object of size bytes. |
| // Small objects are allocated from the per-P cache's free lists. |
| // Large objects (> 32 kB) are allocated straight from the heap. |
| func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer { |
| if gcphase == _GCmarktermination { |
| throw("mallocgc called with gcphase == _GCmarktermination") |
| } |
| |
| if size == 0 { |
| return unsafe.Pointer(&zerobase) |
| } |
| |
| if debug.sbrk != 0 { |
| align := uintptr(16) |
| if typ != nil { |
| align = uintptr(typ.align) |
| } |
| return persistentalloc(size, align, &memstats.other_sys) |
| } |
| |
| // assistG is the G to charge for this allocation, or nil if |
| // GC is not currently active. |
| var assistG *g |
| if gcBlackenEnabled != 0 { |
| // Charge the current user G for this allocation. |
| assistG = getg() |
| if assistG.m.curg != nil { |
| assistG = assistG.m.curg |
| } |
| // Charge the allocation against the G. We'll account |
| // for internal fragmentation at the end of mallocgc. |
| assistG.gcAssistBytes -= int64(size) |
| |
| if assistG.gcAssistBytes < 0 { |
| // This G is in debt. Assist the GC to correct |
| // this before allocating. This must happen |
| // before disabling preemption. |
| gcAssistAlloc(assistG) |
| } |
| } |
| |
| // Set mp.mallocing to keep from being preempted by GC. |
| mp := acquirem() |
| if mp.mallocing != 0 { |
| throw("malloc deadlock") |
| } |
| if mp.gsignal == getg() { |
| throw("malloc during signal") |
| } |
| mp.mallocing = 1 |
| |
| shouldhelpgc := false |
| dataSize := size |
| c := gomcache() |
| var x unsafe.Pointer |
| noscan := typ == nil || typ.kind&kindNoPointers != 0 |
| if size <= maxSmallSize { |
| if noscan && size < maxTinySize { |
| // Tiny allocator. |
| // |
| // Tiny allocator combines several tiny allocation requests |
| // into a single memory block. The resulting memory block |
| // is freed when all subobjects are unreachable. The subobjects |
| // must be noscan (don't have pointers), this ensures that |
| // the amount of potentially wasted memory is bounded. |
| // |
| // Size of the memory block used for combining (maxTinySize) is tunable. |
| // Current setting is 16 bytes, which relates to 2x worst case memory |
| // wastage (when all but one subobjects are unreachable). |
| // 8 bytes would result in no wastage at all, but provides less |
| // opportunities for combining. |
| // 32 bytes provides more opportunities for combining, |
| // but can lead to 4x worst case wastage. |
| // The best case winning is 8x regardless of block size. |
| // |
| // Objects obtained from tiny allocator must not be freed explicitly. |
| // So when an object will be freed explicitly, we ensure that |
| // its size >= maxTinySize. |
| // |
| // SetFinalizer has a special case for objects potentially coming |
| // from tiny allocator, it such case it allows to set finalizers |
| // for an inner byte of a memory block. |
| // |
| // The main targets of tiny allocator are small strings and |
| // standalone escaping variables. On a json benchmark |
| // the allocator reduces number of allocations by ~12% and |
| // reduces heap size by ~20%. |
| off := c.tinyoffset |
| // Align tiny pointer for required (conservative) alignment. |
| if size&7 == 0 { |
| off = round(off, 8) |
| } else if size&3 == 0 { |
| off = round(off, 4) |
| } else if size&1 == 0 { |
| off = round(off, 2) |
| } |
| if off+size <= maxTinySize && c.tiny != 0 { |
| // The object fits into existing tiny block. |
| x = unsafe.Pointer(c.tiny + off) |
| c.tinyoffset = off + size |
| c.local_tinyallocs++ |
| mp.mallocing = 0 |
| releasem(mp) |
| return x |
| } |
| // Allocate a new maxTinySize block. |
| span := c.alloc[tinySpanClass] |
| v := nextFreeFast(span) |
| if v == 0 { |
| v, _, shouldhelpgc = c.nextFree(tinySpanClass) |
| } |
| x = unsafe.Pointer(v) |
| (*[2]uint64)(x)[0] = 0 |
| (*[2]uint64)(x)[1] = 0 |
| // See if we need to replace the existing tiny block with the new one |
| // based on amount of remaining free space. |
| if size < c.tinyoffset || c.tiny == 0 { |
| c.tiny = uintptr(x) |
| c.tinyoffset = size |
| } |
| size = maxTinySize |
| } else { |
| var sizeclass uint8 |
| if size <= smallSizeMax-8 { |
| sizeclass = size_to_class8[(size+smallSizeDiv-1)/smallSizeDiv] |
| } else { |
| sizeclass = size_to_class128[(size-smallSizeMax+largeSizeDiv-1)/largeSizeDiv] |
| } |
| size = uintptr(class_to_size[sizeclass]) |
| spc := makeSpanClass(sizeclass, noscan) |
| span := c.alloc[spc] |
| v := nextFreeFast(span) |
| if v == 0 { |
| v, span, shouldhelpgc = c.nextFree(spc) |
| } |
| x = unsafe.Pointer(v) |
| if needzero && span.needzero != 0 { |
| memclrNoHeapPointers(unsafe.Pointer(v), size) |
| } |
| } |
| } else { |
| var s *mspan |
| shouldhelpgc = true |
| systemstack(func() { |
| s = largeAlloc(size, needzero, noscan) |
| }) |
| s.freeindex = 1 |
| s.allocCount = 1 |
| x = unsafe.Pointer(s.base()) |
| size = s.elemsize |
| } |
| |
| var scanSize uintptr |
| if !noscan { |
| // If allocating a defer+arg block, now that we've picked a malloc size |
| // large enough to hold everything, cut the "asked for" size down to |
| // just the defer header, so that the GC bitmap will record the arg block |
| // as containing nothing at all (as if it were unused space at the end of |
| // a malloc block caused by size rounding). |
| // The defer arg areas are scanned as part of scanstack. |
| if typ == deferType { |
| dataSize = unsafe.Sizeof(_defer{}) |
| } |
| heapBitsSetType(uintptr(x), size, dataSize, typ) |
| if dataSize > typ.size { |
| // Array allocation. If there are any |
| // pointers, GC has to scan to the last |
| // element. |
| if typ.ptrdata != 0 { |
| scanSize = dataSize - typ.size + typ.ptrdata |
| } |
| } else { |
| scanSize = typ.ptrdata |
| } |
| c.local_scan += scanSize |
| } |
| |
| // Ensure that the stores above that initialize x to |
| // type-safe memory and set the heap bits occur before |
| // the caller can make x observable to the garbage |
| // collector. Otherwise, on weakly ordered machines, |
| // the garbage collector could follow a pointer to x, |
| // but see uninitialized memory or stale heap bits. |
| publicationBarrier() |
| |
| // Allocate black during GC. |
| // All slots hold nil so no scanning is needed. |
| // This may be racing with GC so do it atomically if there can be |
| // a race marking the bit. |
| if gcphase != _GCoff { |
| gcmarknewobject(uintptr(x), size, scanSize) |
| } |
| |
| if raceenabled { |
| racemalloc(x, size) |
| } |
| |
| if msanenabled { |
| msanmalloc(x, size) |
| } |
| |
| mp.mallocing = 0 |
| releasem(mp) |
| |
| if debug.allocfreetrace != 0 { |
| tracealloc(x, size, typ) |
| } |
| |
| if rate := MemProfileRate; rate > 0 { |
| if size < uintptr(rate) && int32(size) < c.next_sample { |
| c.next_sample -= int32(size) |
| } else { |
| mp := acquirem() |
| profilealloc(mp, x, size) |
| releasem(mp) |
| } |
| } |
| |
| if assistG != nil { |
| // Account for internal fragmentation in the assist |
| // debt now that we know it. |
| assistG.gcAssistBytes -= int64(size - dataSize) |
| } |
| |
| if shouldhelpgc { |
| if t := (gcTrigger{kind: gcTriggerHeap}); t.test() { |
| gcStart(gcBackgroundMode, t) |
| } |
| } |
| |
| return x |
| } |
| |
| func largeAlloc(size uintptr, needzero bool, noscan bool) *mspan { |
| // print("largeAlloc size=", size, "\n") |
| |
| if size+_PageSize < size { |
| throw("out of memory") |
| } |
| npages := size >> _PageShift |
| if size&_PageMask != 0 { |
| npages++ |
| } |
| |
| // Deduct credit for this span allocation and sweep if |
| // necessary. mHeap_Alloc will also sweep npages, so this only |
| // pays the debt down to npage pages. |
| deductSweepCredit(npages*_PageSize, npages) |
| |
| s := mheap_.alloc(npages, makeSpanClass(0, noscan), true, needzero) |
| if s == nil { |
| throw("out of memory") |
| } |
| s.limit = s.base() + size |
| heapBitsForAddr(s.base()).initSpan(s) |
| return s |
| } |
| |
| // implementation of new builtin |
| // compiler (both frontend and SSA backend) knows the signature |
| // of this function |
| func newobject(typ *_type) unsafe.Pointer { |
| return mallocgc(typ.size, typ, true) |
| } |
| |
| //go:linkname reflect_unsafe_New reflect.unsafe_New |
| func reflect_unsafe_New(typ *_type) unsafe.Pointer { |
| return mallocgc(typ.size, typ, true) |
| } |
| |
| // newarray allocates an array of n elements of type typ. |
| func newarray(typ *_type, n int) unsafe.Pointer { |
| if n == 1 { |
| return mallocgc(typ.size, typ, true) |
| } |
| if n < 0 || uintptr(n) > maxSliceCap(typ.size) { |
| panic(plainError("runtime: allocation size out of range")) |
| } |
| return mallocgc(typ.size*uintptr(n), typ, true) |
| } |
| |
| //go:linkname reflect_unsafe_NewArray reflect.unsafe_NewArray |
| func reflect_unsafe_NewArray(typ *_type, n int) unsafe.Pointer { |
| return newarray(typ, n) |
| } |
| |
| func profilealloc(mp *m, x unsafe.Pointer, size uintptr) { |
| mp.mcache.next_sample = nextSample() |
| mProf_Malloc(x, size) |
| } |
| |
| // nextSample returns the next sampling point for heap profiling. The goal is |
| // to sample allocations on average every MemProfileRate bytes, but with a |
| // completely random distribution over the allocation timeline; this |
| // corresponds to a Poisson process with parameter MemProfileRate. In Poisson |
| // processes, the distance between two samples follows the exponential |
| // distribution (exp(MemProfileRate)), so the best return value is a random |
| // number taken from an exponential distribution whose mean is MemProfileRate. |
| func nextSample() int32 { |
| if GOOS == "plan9" { |
| // Plan 9 doesn't support floating point in note handler. |
| if g := getg(); g == g.m.gsignal { |
| return nextSampleNoFP() |
| } |
| } |
| |
| return fastexprand(MemProfileRate) |
| } |
| |
| // fastexprand returns a random number from an exponential distribution with |
| // the specified mean. |
| func fastexprand(mean int) int32 { |
| // Avoid overflow. Maximum possible step is |
| // -ln(1/(1<<randomBitCount)) * mean, approximately 20 * mean. |
| switch { |
| case mean > 0x7000000: |
| mean = 0x7000000 |
| case mean == 0: |
| return 0 |
| } |
| |
| // Take a random sample of the exponential distribution exp(-mean*x). |
| // The probability distribution function is mean*exp(-mean*x), so the CDF is |
| // p = 1 - exp(-mean*x), so |
| // q = 1 - p == exp(-mean*x) |
| // log_e(q) = -mean*x |
| // -log_e(q)/mean = x |
| // x = -log_e(q) * mean |
| // x = log_2(q) * (-log_e(2)) * mean ; Using log_2 for efficiency |
| const randomBitCount = 26 |
| q := fastrand()%(1<<randomBitCount) + 1 |
| qlog := fastlog2(float64(q)) - randomBitCount |
| if qlog > 0 { |
| qlog = 0 |
| } |
| const minusLog2 = -0.6931471805599453 // -ln(2) |
| return int32(qlog*(minusLog2*float64(mean))) + 1 |
| } |
| |
| // nextSampleNoFP is similar to nextSample, but uses older, |
| // simpler code to avoid floating point. |
| func nextSampleNoFP() int32 { |
| // Set first allocation sample size. |
| rate := MemProfileRate |
| if rate > 0x3fffffff { // make 2*rate not overflow |
| rate = 0x3fffffff |
| } |
| if rate != 0 { |
| return int32(fastrand() % uint32(2*rate)) |
| } |
| return 0 |
| } |
| |
| type persistentAlloc struct { |
| base *notInHeap |
| off uintptr |
| } |
| |
| var globalAlloc struct { |
| mutex |
| persistentAlloc |
| } |
| |
| // Wrapper around sysAlloc that can allocate small chunks. |
| // There is no associated free operation. |
| // Intended for things like function/type/debug-related persistent data. |
| // If align is 0, uses default align (currently 8). |
| // The returned memory will be zeroed. |
| // |
| // Consider marking persistentalloc'd types go:notinheap. |
| func persistentalloc(size, align uintptr, sysStat *uint64) unsafe.Pointer { |
| var p *notInHeap |
| systemstack(func() { |
| p = persistentalloc1(size, align, sysStat) |
| }) |
| return unsafe.Pointer(p) |
| } |
| |
| // Must run on system stack because stack growth can (re)invoke it. |
| // See issue 9174. |
| //go:systemstack |
| func persistentalloc1(size, align uintptr, sysStat *uint64) *notInHeap { |
| const ( |
| chunk = 256 << 10 |
| maxBlock = 64 << 10 // VM reservation granularity is 64K on windows |
| ) |
| |
| if size == 0 { |
| throw("persistentalloc: size == 0") |
| } |
| if align != 0 { |
| if align&(align-1) != 0 { |
| throw("persistentalloc: align is not a power of 2") |
| } |
| if align > _PageSize { |
| throw("persistentalloc: align is too large") |
| } |
| } else { |
| align = 8 |
| } |
| |
| if size >= maxBlock { |
| return (*notInHeap)(sysAlloc(size, sysStat)) |
| } |
| |
| mp := acquirem() |
| var persistent *persistentAlloc |
| if mp != nil && mp.p != 0 { |
| persistent = &mp.p.ptr().palloc |
| } else { |
| lock(&globalAlloc.mutex) |
| persistent = &globalAlloc.persistentAlloc |
| } |
| persistent.off = round(persistent.off, align) |
| if persistent.off+size > chunk || persistent.base == nil { |
| persistent.base = (*notInHeap)(sysAlloc(chunk, &memstats.other_sys)) |
| if persistent.base == nil { |
| if persistent == &globalAlloc.persistentAlloc { |
| unlock(&globalAlloc.mutex) |
| } |
| throw("runtime: cannot allocate memory") |
| } |
| persistent.off = 0 |
| } |
| p := persistent.base.add(persistent.off) |
| persistent.off += size |
| releasem(mp) |
| if persistent == &globalAlloc.persistentAlloc { |
| unlock(&globalAlloc.mutex) |
| } |
| |
| if sysStat != &memstats.other_sys { |
| mSysStatInc(sysStat, size) |
| mSysStatDec(&memstats.other_sys, size) |
| } |
| return p |
| } |
| |
| // linearAlloc is a simple linear allocator that pre-reserves a region |
| // of memory and then maps that region as needed. The caller is |
| // responsible for locking. |
| type linearAlloc struct { |
| next uintptr // next free byte |
| mapped uintptr // one byte past end of mapped space |
| end uintptr // end of reserved space |
| } |
| |
| func (l *linearAlloc) init(base, size uintptr) { |
| l.next, l.mapped = base, base |
| l.end = base + size |
| } |
| |
| func (l *linearAlloc) alloc(size, align uintptr, sysStat *uint64) unsafe.Pointer { |
| p := round(l.next, align) |
| if p+size > l.end { |
| return nil |
| } |
| l.next = p + size |
| if pEnd := round(l.next-1, physPageSize); pEnd > l.mapped { |
| // We need to map more of the reserved space. |
| sysMap(unsafe.Pointer(l.mapped), pEnd-l.mapped, sysStat) |
| l.mapped = pEnd |
| } |
| return unsafe.Pointer(p) |
| } |
| |
| // notInHeap is off-heap memory allocated by a lower-level allocator |
| // like sysAlloc or persistentAlloc. |
| // |
| // In general, it's better to use real types marked as go:notinheap, |
| // but this serves as a generic type for situations where that isn't |
| // possible (like in the allocators). |
| // |
| // TODO: Use this as the return type of sysAlloc, persistentAlloc, etc? |
| // |
| //go:notinheap |
| type notInHeap struct{} |
| |
| func (p *notInHeap) add(bytes uintptr) *notInHeap { |
| return (*notInHeap)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + bytes)) |
| } |