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Diffstat (limited to 'src/runtime/malloc.go')
| -rw-r--r-- | src/runtime/malloc.go | 1452 |
1 files changed, 1452 insertions, 0 deletions
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go new file mode 100644 index 0000000..f20ded5 --- /dev/null +++ b/src/runtime/malloc.go @@ -0,0 +1,1452 @@ +// 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 in-use 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's +// pages are returned to the mheap and the mspan is now dead. +// +// Allocating and freeing a large object uses the mheap +// directly, bypassing the mcache and mcentral. +// +// If mspan.needzero is false, then free object slots in the mspan are +// already zeroed. Otherwise 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/math" + "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 + + 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 + + // 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 most 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. On Linux, Go leans on stricter 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. + // + // On ios/arm64, although 64-bit pointers are presumably + // available, pointers are truncated to 33 bits. Furthermore, + // only the top 4 GiB of the address space are actually available + // to the application, but we allow the whole 33 bits anyway for + // simplicity. + // TODO(mknyszek): Consider limiting it to 32 bits and using + // arenaBaseOffset to offset into the top 4 GiB. + // + // WebAssembly currently has a limit of 4GB linear memory. + heapAddrBits = (_64bit*(1-sys.GoarchWasm)*(1-sys.GoosIos*sys.GoarchArm64))*48 + (1-_64bit+sys.GoarchWasm)*(32-(sys.GoarchMips+sys.GoarchMipsle)) + 33*sys.GoosIos*sys.GoarchArm64 + + // 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 << addr bits) = arena size * L1 entries * L2 entries + // + // Currently, we balance these as follows: + // + // Platform Addr bits Arena size L1 entries L2 entries + // -------------- --------- ---------- ---------- ----------- + // */64-bit 48 64MB 1 4M (32MB) + // windows/64-bit 48 4MB 64 1M (8MB) + // */32-bit 32 4MB 1 1024 (4KB) + // */mips(le) 31 4MB 1 512 (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)*(1-sys.GoarchWasm)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm + + // 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 aix/ppc64, this offset allows to keep the heapAddrBits to + // 48. Otherwize, it would be 60 in order to handle mmap addresses + // (in range 0x0a00000000000000 - 0x0afffffffffffff). But in this + // case, the memory reserved in (s *pageAlloc).init for chunks + // is causing important slowdowns. + // + // On other platforms, the user address space is contiguous + // and starts at 0, so no offset is necessary. + arenaBaseOffset = 0xffff800000000000*sys.GoarchAmd64 + 0x0a00000000000000*sys.GoosAix + // A typed version of this constant that will make it into DWARF (for viewcore). + arenaBaseOffsetUintptr = uintptr(arenaBaseOffset) + + // 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 + +// physHugePageSize is the size in bytes of the OS's default physical huge +// page size whose allocation is opaque to the application. It is assumed +// and verified to be a power of two. +// +// If set, this must be set by the OS init code (typically in osinit) before +// mallocinit. However, setting it at all is optional, and leaving the default +// value is always safe (though potentially less efficient). +// +// Since physHugePageSize is always assumed to be a power of two, +// physHugePageShift is defined as physHugePageSize == 1 << physHugePageShift. +// The purpose of physHugePageShift is to avoid doing divisions in +// performance critical functions. +var ( + physHugePageSize uintptr + physHugePageShift uint +) + +// OS memory management abstraction layer +// +// Regions of the address space managed by the runtime may be in one of four +// states at any given time: +// 1) None - Unreserved and unmapped, the default state of any region. +// 2) Reserved - Owned by the runtime, but accessing it would cause a fault. +// Does not count against the process' memory footprint. +// 3) Prepared - Reserved, intended not to be backed by physical memory (though +// an OS may implement this lazily). Can transition efficiently to +// Ready. Accessing memory in such a region is undefined (may +// fault, may give back unexpected zeroes, etc.). +// 4) Ready - may be accessed safely. +// +// This set of states is more than is strictly necessary to support all the +// currently supported platforms. One could get by with just None, Reserved, and +// Ready. However, the Prepared state gives us flexibility for performance +// purposes. For example, on POSIX-y operating systems, Reserved is usually a +// private anonymous mmap'd region with PROT_NONE set, and to transition +// to Ready would require setting PROT_READ|PROT_WRITE. However the +// underspecification of Prepared lets us use just MADV_FREE to transition from +// Ready to Prepared. Thus with the Prepared state we can set the permission +// bits just once early on, we can efficiently tell the OS that it's free to +// take pages away from us when we don't strictly need them. +// +// For each OS there is a common set of helpers defined that transition +// memory regions between these states. The helpers are as follows: +// +// sysAlloc transitions an OS-chosen region of memory from None to Ready. +// More specifically, it obtains a large chunk of zeroed memory from the +// operating system, typically on the order of a hundred kilobytes +// or a megabyte. This memory is always immediately available for use. +// +// sysFree transitions a memory region from any state to None. Therefore, it +// returns memory unconditionally. It is used if an out-of-memory error has been +// detected midway through an allocation or to carve out an aligned section of +// the address space. It is okay if sysFree is a no-op only if sysReserve always +// returns a memory region aligned to the heap allocator's alignment +// restrictions. +// +// sysReserve transitions a memory region from None to Reserved. It reserves +// address space in such a way that it would cause a fatal fault upon access +// (either via permissions or not committing the memory). Such a reservation is +// thus never backed by physical 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 sysReserve. +// +// sysMap transitions a memory region from Reserved to Prepared. It ensures the +// memory region can be efficiently transitioned to Ready. +// +// sysUsed transitions a memory region from Prepared to Ready. It notifies the +// operating system that the memory region is needed and ensures that the region +// may be safely accessed. This is typically a no-op on systems that don't have +// an explicit commit step and hard over-commit limits, but is critical on +// Windows, for example. +// +// sysUnused transitions a memory region from Ready to Prepared. It notifies the +// operating system that the physical pages backing this memory region are no +// longer needed and can be reused for other purposes. The contents of a +// sysUnused memory region are considered forfeit and the region must not be +// accessed again until sysUsed is called. +// +// sysFault transitions a memory region from Ready or Prepared to Reserved. It +// marks a region such that it will always 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 > maxPhysPageSize { + print("system page size (", physPageSize, ") is larger than maximum page size (", maxPhysPageSize, ")\n") + throw("bad 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") + } + if physHugePageSize&(physHugePageSize-1) != 0 { + print("system huge page size (", physHugePageSize, ") must be a power of 2\n") + throw("bad system huge page size") + } + if physHugePageSize > maxPhysHugePageSize { + // physHugePageSize is greater than the maximum supported huge page size. + // Don't throw here, like in the other cases, since a system configured + // in this way isn't wrong, we just don't have the code to support them. + // Instead, silently set the huge page size to zero. + physHugePageSize = 0 + } + if physHugePageSize != 0 { + // Since physHugePageSize is a power of 2, it suffices to increase + // physHugePageShift until 1<<physHugePageShift == physHugePageSize. + for 1<<physHugePageShift != physHugePageSize { + physHugePageShift++ + } + } + if pagesPerArena%pagesPerSpanRoot != 0 { + print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerSpanRoot (", pagesPerSpanRoot, ")\n") + throw("bad pagesPerSpanRoot") + } + if pagesPerArena%pagesPerReclaimerChunk != 0 { + print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerReclaimerChunk (", pagesPerReclaimerChunk, ")\n") + throw("bad pagesPerReclaimerChunk") + } + + // Initialize the heap. + mheap_.init() + mcache0 = allocmcache() + lockInit(&gcBitsArenas.lock, lockRankGcBitsArenas) + lockInit(&proflock, lockRankProf) + lockInit(&globalAlloc.mutex, lockRankGlobalAlloc) + + // 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 ios/arm64, the address space is even smaller. + // + // On AIX, mmaps starts at 0x0A00000000000000 for 64-bit. + // processes. + for i := 0x7f; i >= 0; i-- { + var p uintptr + switch { + case raceenabled: + // The TSAN runtime requires the heap + // to be in the range [0x00c000000000, + // 0x00e000000000). + p = uintptr(i)<<32 | uintptrMask&(0x00c0<<32) + if p >= uintptrMask&0x00e000000000 { + continue + } + case GOARCH == "arm64" && GOOS == "ios": + p = uintptr(i)<<40 | uintptrMask&(0x0013<<28) + case GOARCH == "arm64": + p = uintptr(i)<<40 | uintptrMask&(0x0040<<32) + case GOOS == "aix": + if i == 0 { + // We don't use addresses directly after 0x0A00000000000000 + // to avoid collisions with others mmaps done by non-go programs. + continue + } + p = uintptr(i)<<40 | uintptrMask&(0xa0<<52) + 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 = (1 << arenaBits) * unsafe.Sizeof(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 = alignUp(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 = mheap_.arena.end // 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. +// +// sysAlloc returns a memory region in the Prepared state. This region must +// be transitioned to Ready before use. +// +// h must be locked. +func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) { + assertLockHeld(&h.lock) + + n = alignUp(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 simplify 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") + } + + // Transition from Reserved to Prepared. + 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.gcMiscSys)) + if r == nil { + r = (*heapArena)(persistentalloc(unsafe.Sizeof(*r), sys.PtrSize, &memstats.gcMiscSys)) + if r == nil { + throw("out of memory allocating heap arena metadata") + } + } + + // Add the arena to the arenas list. + if len(h.allArenas) == cap(h.allArenas) { + size := 2 * uintptr(cap(h.allArenas)) * sys.PtrSize + if size == 0 { + size = physPageSize + } + newArray := (*notInHeap)(persistentalloc(size, sys.PtrSize, &memstats.gcMiscSys)) + if newArray == nil { + throw("out of memory allocating allArenas") + } + oldSlice := h.allArenas + *(*notInHeapSlice)(unsafe.Pointer(&h.allArenas)) = notInHeapSlice{newArray, len(h.allArenas), int(size / sys.PtrSize)} + copy(h.allArenas, oldSlice) + // Do not free the old backing array because + // there may be concurrent readers. Since we + // double the array each time, this can lead + // to at most 2x waste. + } + h.allArenas = h.allArenas[:len(h.allArenas)+1] + h.allArenas[len(h.allArenas)-1] = ri + + // 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 = alignUp(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 := alignUp(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. +// +// Must run in a non-preemptible context since otherwise the owner of +// c could change. +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") + } + 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.malloc { + if debug.sbrk != 0 { + align := uintptr(16) + if typ != nil { + // TODO(austin): This should be just + // align = uintptr(typ.align) + // but that's only 4 on 32-bit platforms, + // even if there's a uint64 field in typ (see #599). + // This causes 64-bit atomic accesses to panic. + // Hence, we use stricter alignment that matches + // the normal allocator better. + if size&7 == 0 { + align = 8 + } else if size&3 == 0 { + align = 4 + } else if size&1 == 0 { + align = 2 + } else { + align = 1 + } + } + return persistentalloc(size, align, &memstats.other_sys) + } + + if inittrace.active && inittrace.id == getg().goid { + // Init functions are executed sequentially in a single Go routine. + inittrace.allocs += 1 + } + } + + // 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 := getMCache() + if c == nil { + throw("mallocgc called without a P or outside bootstrapping") + } + var span *mspan + var x unsafe.Pointer + noscan := typ == nil || typ.ptrdata == 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 = alignUp(off, 8) + } else if sys.PtrSize == 4 && size == 12 { + // Conservatively align 12-byte objects to 8 bytes on 32-bit + // systems so that objects whose first field is a 64-bit + // value is aligned to 8 bytes and does not cause a fault on + // atomic access. See issue 37262. + // TODO(mknyszek): Remove this workaround if/when issue 36606 + // is resolved. + off = alignUp(off, 8) + } else if size&3 == 0 { + off = alignUp(off, 4) + } else if size&1 == 0 { + off = alignUp(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.tinyAllocs++ + mp.mallocing = 0 + releasem(mp) + return x + } + // Allocate a new maxTinySize block. + span = c.alloc[tinySpanClass] + v := nextFreeFast(span) + if v == 0 { + v, span, 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[divRoundUp(size, smallSizeDiv)] + } else { + sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, 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 { + shouldhelpgc = true + span = c.allocLarge(size, needzero, noscan) + span.freeindex = 1 + span.allocCount = 1 + x = unsafe.Pointer(span.base()) + size = span.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.scanAlloc += 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(span, uintptr(x), size, scanSize) + } + + if raceenabled { + racemalloc(x, size) + } + + if msanenabled { + msanmalloc(x, size) + } + + mp.mallocing = 0 + releasem(mp) + + if debug.malloc { + if debug.allocfreetrace != 0 { + tracealloc(x, size, typ) + } + + if inittrace.active && inittrace.id == getg().goid { + // Init functions are executed sequentially in a single Go routine. + inittrace.bytes += uint64(size) + } + } + + if rate := MemProfileRate; rate > 0 { + if rate != 1 && size < c.nextSample { + c.nextSample -= 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(t) + } + } + + return x +} + +// 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) +} + +//go:linkname reflectlite_unsafe_New internal/reflectlite.unsafe_New +func reflectlite_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) + } + mem, overflow := math.MulUintptr(typ.size, uintptr(n)) + if overflow || mem > maxAlloc || n < 0 { + panic(plainError("runtime: allocation size out of range")) + } + return mallocgc(mem, 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) { + c := getMCache() + if c == nil { + throw("profilealloc called without a P or outside bootstrapping") + } + c.nextSample = 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() uintptr { + if MemProfileRate == 1 { + // Callers assign our return value to + // mcache.next_sample, but next_sample is not used + // when the rate is 1. So avoid the math below and + // just return something. + return 0 + } + if GOOS == "plan9" { + // Plan 9 doesn't support floating point in note handler. + if g := getg(); g == g.m.gsignal { + return nextSampleNoFP() + } + } + + return uintptr(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() uintptr { + // Set first allocation sample size. + rate := MemProfileRate + if rate > 0x3fffffff { // make 2*rate not overflow + rate = 0x3fffffff + } + if rate != 0 { + return uintptr(fastrand() % uint32(2*rate)) + } + return 0 +} + +type persistentAlloc struct { + base *notInHeap + off uintptr +} + +var globalAlloc struct { + mutex + persistentAlloc +} + +// persistentChunkSize is the number of bytes we allocate when we grow +// a persistentAlloc. +const persistentChunkSize = 256 << 10 + +// persistentChunks is a list of all the persistent chunks we have +// allocated. The list is maintained through the first word in the +// persistent chunk. This is updated atomically. +var persistentChunks *notInHeap + +// 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 *sysMemStat) 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 *sysMemStat) *notInHeap { + const ( + 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 = alignUp(persistent.off, align) + if persistent.off+size > persistentChunkSize || persistent.base == nil { + persistent.base = (*notInHeap)(sysAlloc(persistentChunkSize, &memstats.other_sys)) + if persistent.base == nil { + if persistent == &globalAlloc.persistentAlloc { + unlock(&globalAlloc.mutex) + } + throw("runtime: cannot allocate memory") + } + + // Add the new chunk to the persistentChunks list. + for { + chunks := uintptr(unsafe.Pointer(persistentChunks)) + *(*uintptr)(unsafe.Pointer(persistent.base)) = chunks + if atomic.Casuintptr((*uintptr)(unsafe.Pointer(&persistentChunks)), chunks, uintptr(unsafe.Pointer(persistent.base))) { + break + } + } + persistent.off = alignUp(sys.PtrSize, align) + } + p := persistent.base.add(persistent.off) + persistent.off += size + releasem(mp) + if persistent == &globalAlloc.persistentAlloc { + unlock(&globalAlloc.mutex) + } + + if sysStat != &memstats.other_sys { + sysStat.add(int64(size)) + memstats.other_sys.add(-int64(size)) + } + return p +} + +// inPersistentAlloc reports whether p points to memory allocated by +// persistentalloc. This must be nosplit because it is called by the +// cgo checker code, which is called by the write barrier code. +//go:nosplit +func inPersistentAlloc(p uintptr) bool { + chunk := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&persistentChunks))) + for chunk != 0 { + if p >= chunk && p < chunk+persistentChunkSize { + return true + } + chunk = *(*uintptr)(unsafe.Pointer(chunk)) + } + return false +} + +// linearAlloc is a simple linear allocator that pre-reserves a region +// of memory and then maps that region into the Ready state 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) { + if base+size < base { + // Chop off the last byte. The runtime isn't prepared + // to deal with situations where the bounds could overflow. + // Leave that memory reserved, though, so we don't map it + // later. + size -= 1 + } + l.next, l.mapped = base, base + l.end = base + size +} + +func (l *linearAlloc) alloc(size, align uintptr, sysStat *sysMemStat) unsafe.Pointer { + p := alignUp(l.next, align) + if p+size > l.end { + return nil + } + l.next = p + size + if pEnd := alignUp(l.next-1, physPageSize); pEnd > l.mapped { + // Transition from Reserved to Prepared to Ready. + sysMap(unsafe.Pointer(l.mapped), pEnd-l.mapped, sysStat) + sysUsed(unsafe.Pointer(l.mapped), pEnd-l.mapped) + 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)) +} |