| // 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 ( |
| "internal/goarch" |
| "internal/goos" |
| "internal/runtime/atomic" |
| "internal/runtime/math" |
| "internal/runtime/sys" |
| "unsafe" |
| ) |
| |
| const ( |
| maxTinySize = _TinySize |
| tinySizeClass = _TinySizeClass |
| maxSmallSize = _MaxSmallSize |
| |
| pageShift = _PageShift |
| pageSize = _PageSize |
| |
| _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 - goarch.PtrSize/4*goos.IsWindows - 1*goos.IsPlan9 |
| |
| // 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 in iOS <14. |
| // Furthermore, only the top 4 GiB of the address space are |
| // actually available to the application. In iOS >=14, more |
| // of the address space is available, and the OS can now |
| // provide addresses outside of those 33 bits. Pick 40 bits |
| // as a reasonable balance between address space usage by the |
| // page allocator, and flexibility for what mmap'd regions |
| // we'll accept for the heap. We can't just move to the full |
| // 48 bits because this uses too much address space for older |
| // iOS versions. |
| // TODO(mknyszek): Once iOS <14 is deprecated, promote ios/arm64 |
| // to a 48-bit address space like every other arm64 platform. |
| // |
| // WebAssembly currently has a limit of 4GB linear memory. |
| heapAddrBits = (_64bit*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64))*48 + (1-_64bit+goarch.IsWasm)*(32-(goarch.IsMips+goarch.IsMipsle)) + 40*goos.IsIos*goarch.IsArm64 |
| |
| // 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) |
| // ios/arm64 40 4MB 1 256K (2MB) |
| // */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 |
| |
| heapArenaWords = heapArenaBytes / goarch.PtrSize |
| |
| // 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-goos.IsWindows)*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64)) + (2+20)*(_64bit*goos.IsWindows) + (2+20)*(1-_64bit) + (2+20)*goarch.IsWasm + (2+20)*goos.IsIos*goarch.IsArm64 |
| |
| // heapArenaBitmapWords is the size of each heap arena's bitmap in uintptrs. |
| heapArenaBitmapWords = heapArenaWords / (8 * goarch.PtrSize) |
| |
| 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 * goos.IsWindows) |
| |
| // 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. Otherwise, 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*goarch.IsAmd64 + 0x0a00000000000000*goos.IsAix |
| // 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 |
| |
| // minHeapForMetadataHugePages sets a threshold on when certain kinds of |
| // heap metadata, currently the arenas map L2 entries and page alloc bitmap |
| // mappings, are allowed to be backed by huge pages. If the heap goal ever |
| // exceeds this threshold, then huge pages are enabled. |
| // |
| // These numbers are chosen with the assumption that huge pages are on the |
| // order of a few MiB in size. |
| // |
| // The kind of metadata this applies to has a very low overhead when compared |
| // to address space used, but their constant overheads for small heaps would |
| // be very high if they were to be backed by huge pages (e.g. a few MiB makes |
| // a huge difference for an 8 MiB heap, but barely any difference for a 1 GiB |
| // heap). The benefit of huge pages is also not worth it for small heaps, |
| // because only a very, very small part of the metadata is used for small heaps. |
| // |
| // N.B. If the heap goal exceeds the threshold then shrinks to a very small size |
| // again, then huge pages will still be enabled for this mapping. The reason is that |
| // there's no point unless we're also returning the physical memory for these |
| // metadata mappings back to the OS. That would be quite complex to do in general |
| // as the heap is likely fragmented after a reduction in heap size. |
| minHeapForMetadataHugePages = 1 << 30 |
| ) |
| |
| // 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 |
| ) |
| |
| func mallocinit() { |
| if class_to_size[_TinySizeClass] != _TinySize { |
| throw("bad TinySizeClass") |
| } |
| |
| if heapArenaBitmapWords&(heapArenaBitmapWords-1) != 0 { |
| // heapBits expects modular arithmetic on bitmap |
| // addresses to work. |
| throw("heapArenaBitmapWords not a power of 2") |
| } |
| |
| // 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") |
| } |
| // Check that the minimum size (exclusive) for a malloc header is also |
| // a size class boundary. This is important to making sure checks align |
| // across different parts of the runtime. |
| minSizeForMallocHeaderIsSizeClass := false |
| for i := 0; i < len(class_to_size); i++ { |
| if minSizeForMallocHeader == uintptr(class_to_size[i]) { |
| minSizeForMallocHeaderIsSizeClass = true |
| break |
| } |
| } |
| if !minSizeForMallocHeaderIsSizeClass { |
| throw("min size of malloc header is not a size class boundary") |
| } |
| // Check that the pointer bitmap for all small sizes without a malloc header |
| // fits in a word. |
| if minSizeForMallocHeader/goarch.PtrSize > 8*goarch.PtrSize { |
| throw("max pointer/scan bitmap size for headerless objects is too large") |
| } |
| |
| if minTagBits > taggedPointerBits { |
| throw("taggedPointerbits too small") |
| } |
| |
| // Initialize the heap. |
| mheap_.init() |
| mcache0 = allocmcache() |
| lockInit(&gcBitsArenas.lock, lockRankGcBitsArenas) |
| lockInit(&profInsertLock, lockRankProfInsert) |
| lockInit(&profBlockLock, lockRankProfBlock) |
| lockInit(&profMemActiveLock, lockRankProfMemActive) |
| for i := range profMemFutureLock { |
| lockInit(&profMemFutureLock[i], lockRankProfMemFuture) |
| } |
| lockInit(&globalAlloc.mutex, lockRankGlobalAlloc) |
| |
| // Create initial arena growth hints. |
| if goarch.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. |
| // |
| // Space mapped for user arenas comes immediately after the range |
| // originally reserved for the regular heap when race mode is not |
| // enabled because user arena chunks can never be used for regular heap |
| // allocations and we want to avoid fragmenting the address space. |
| // |
| // In race mode we have no choice but to just use the same hints because |
| // the race detector requires that the heap be mapped contiguously. |
| 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) |
| } |
| // Switch to generating hints for user arenas if we've gone |
| // through about half the hints. In race mode, take only about |
| // a quarter; we don't have very much space to work with. |
| hintList := &mheap_.arenaHints |
| if (!raceenabled && i > 0x3f) || (raceenabled && i > 0x5f) { |
| hintList = &mheap_.userArena.arenaHints |
| } |
| hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc()) |
| hint.addr = p |
| hint.next, *hintList = *hintList, 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, true) |
| } |
| |
| // 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, false) |
| p = mheap_.arena.end // For hint below |
| break |
| } |
| } |
| hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc()) |
| hint.addr = p |
| hint.next, mheap_.arenaHints = mheap_.arenaHints, hint |
| |
| // Place the hint for user arenas just after the large reservation. |
| // |
| // While this potentially competes with the hint above, in practice we probably |
| // aren't going to be getting this far anyway on 32-bit platforms. |
| userArenaHint := (*arenaHint)(mheap_.arenaHintAlloc.alloc()) |
| userArenaHint.addr = p |
| userArenaHint.next, mheap_.userArena.arenaHints = mheap_.userArena.arenaHints, userArenaHint |
| } |
| // Initialize the memory limit here because the allocator is going to look at it |
| // but we haven't called gcinit yet and we're definitely going to allocate memory before then. |
| gcController.memoryLimit.Store(maxInt64) |
| } |
| |
| // 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. |
| // |
| // hintList is a list of hint addresses for where to allocate new |
| // heap arenas. It must be non-nil. |
| // |
| // register indicates whether the heap arena should be registered |
| // in allArenas. |
| // |
| // sysAlloc returns a memory region in the Reserved state. This region must |
| // be transitioned to Prepared and then Ready before use. |
| // |
| // h must be locked. |
| func (h *mheap) sysAlloc(n uintptr, hintList **arenaHint, register bool) (v unsafe.Pointer, size uintptr) { |
| assertLockHeld(&h.lock) |
| |
| n = alignUp(n, heapArenaBytes) |
| |
| if hintList == &h.arenaHints { |
| // First, try the arena pre-reservation. |
| // Newly-used mappings are considered released. |
| // |
| // Only do this if we're using the regular heap arena hints. |
| // This behavior is only for the heap. |
| v = h.arena.alloc(n, heapArenaBytes, &gcController.heapReleased) |
| if v != nil { |
| size = n |
| goto mapped |
| } |
| } |
| |
| // Try to grow the heap at a hint address. |
| for *hintList != nil { |
| hint := *hintList |
| 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 { |
| sysFreeOS(v, n) |
| } |
| *hintList = 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") |
| } |
| |
| 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. |
| // |
| // Use sysAllocOS instead of sysAlloc or persistentalloc because there's no |
| // statistic we can comfortably account for this space in. With this structure, |
| // we rely on demand paging to avoid large overheads, but tracking which memory |
| // is paged in is too expensive. Trying to account for the whole region means |
| // that it will appear like an enormous memory overhead in statistics, even though |
| // it is not. |
| l2 = (*[1 << arenaL2Bits]*heapArena)(sysAllocOS(unsafe.Sizeof(*l2))) |
| if l2 == nil { |
| throw("out of memory allocating heap arena map") |
| } |
| if h.arenasHugePages { |
| sysHugePage(unsafe.Pointer(l2), unsafe.Sizeof(*l2)) |
| } else { |
| sysNoHugePage(unsafe.Pointer(l2), unsafe.Sizeof(*l2)) |
| } |
| 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), goarch.PtrSize, &memstats.gcMiscSys)) |
| if r == nil { |
| r = (*heapArena)(persistentalloc(unsafe.Sizeof(*r), goarch.PtrSize, &memstats.gcMiscSys)) |
| if r == nil { |
| throw("out of memory allocating heap arena metadata") |
| } |
| } |
| |
| // Register the arena in allArenas if requested. |
| if register { |
| if len(h.allArenas) == cap(h.allArenas) { |
| size := 2 * uintptr(cap(h.allArenas)) * goarch.PtrSize |
| if size == 0 { |
| size = physPageSize |
| } |
| newArray := (*notInHeap)(persistentalloc(size, goarch.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 / goarch.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: |
| 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. |
| sysFreeOS(unsafe.Pointer(p), size+align) |
| p = alignUp(p, align) |
| p2 := sysReserve(unsafe.Pointer(p), size) |
| if p != uintptr(p2) { |
| // Must have raced. Try again. |
| sysFreeOS(p2, size) |
| 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) |
| sysFreeOS(unsafe.Pointer(p), pAligned-p) |
| end := pAligned + size |
| endLen := (p + size + align) - end |
| if endLen > 0 { |
| sysFreeOS(unsafe.Pointer(end), endLen) |
| } |
| return unsafe.Pointer(pAligned), size |
| } |
| } |
| |
| // enableMetadataHugePages enables huge pages for various sources of heap metadata. |
| // |
| // A note on latency: for sufficiently small heaps (<10s of GiB) this function will take constant |
| // time, but may take time proportional to the size of the mapped heap beyond that. |
| // |
| // This function is idempotent. |
| // |
| // The heap lock must not be held over this operation, since it will briefly acquire |
| // the heap lock. |
| // |
| // Must be called on the system stack because it acquires the heap lock. |
| // |
| //go:systemstack |
| func (h *mheap) enableMetadataHugePages() { |
| // Enable huge pages for page structure. |
| h.pages.enableChunkHugePages() |
| |
| // Grab the lock and set arenasHugePages if it's not. |
| // |
| // Once arenasHugePages is set, all new L2 entries will be eligible for |
| // huge pages. We'll set all the old entries after we release the lock. |
| lock(&h.lock) |
| if h.arenasHugePages { |
| unlock(&h.lock) |
| return |
| } |
| h.arenasHugePages = true |
| unlock(&h.lock) |
| |
| // N.B. The arenas L1 map is quite small on all platforms, so it's fine to |
| // just iterate over the whole thing. |
| for i := range h.arenas { |
| l2 := (*[1 << arenaL2Bits]*heapArena)(atomic.Loadp(unsafe.Pointer(&h.arenas[i]))) |
| if l2 == nil { |
| continue |
| } |
| sysHugePage(unsafe.Pointer(l2), unsafe.Sizeof(*l2)) |
| } |
| } |
| |
| // 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.TrailingZeros64(s.allocCache) // Is there a free object in the allocCache? |
| if theBit < 64 { |
| result := s.freeindex + uint16(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(uintptr(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 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(uintptr(freeIndex)*s.elemsize + s.base()) |
| s.allocCount++ |
| if 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. |
| // |
| // mallocgc should be an internal detail, |
| // but widely used packages access it using linkname. |
| // Notable members of the hall of shame include: |
| // - github.com/bytedance/gopkg |
| // - github.com/bytedance/sonic |
| // - github.com/cloudwego/frugal |
| // - github.com/cockroachdb/cockroach |
| // - github.com/cockroachdb/pebble |
| // - github.com/ugorji/go/codec |
| // |
| // Do not remove or change the type signature. |
| // See go.dev/issue/67401. |
| // |
| //go:linkname mallocgc |
| 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) |
| } |
| |
| // It's possible for any malloc to trigger sweeping, which may in |
| // turn queue finalizers. Record this dynamic lock edge. |
| lockRankMayQueueFinalizer() |
| |
| userSize := size |
| if asanenabled { |
| // Refer to ASAN runtime library, the malloc() function allocates extra memory, |
| // the redzone, around the user requested memory region. And the redzones are marked |
| // as unaddressable. We perform the same operations in Go to detect the overflows or |
| // underflows. |
| size += computeRZlog(size) |
| } |
| |
| 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 goroutine. |
| inittrace.allocs += 1 |
| } |
| } |
| |
| // assistG is the G to charge for this allocation, or nil if |
| // GC is not currently active. |
| assistG := deductAssistCredit(size) |
| |
| // 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 := userSize |
| c := getMCache(mp) |
| if c == nil { |
| throw("mallocgc called without a P or outside bootstrapping") |
| } |
| var span *mspan |
| var header **_type |
| var x unsafe.Pointer |
| noscan := typ == nil || !typ.Pointers() |
| // In some cases block zeroing can profitably (for latency reduction purposes) |
| // be delayed till preemption is possible; delayedZeroing tracks that state. |
| delayedZeroing := false |
| // Determine if it's a 'small' object that goes into a size-classed span. |
| // |
| // Note: This comparison looks a little strange, but it exists to smooth out |
| // the crossover between the largest size class and large objects that have |
| // their own spans. The small window of object sizes between maxSmallSize-mallocHeaderSize |
| // and maxSmallSize will be considered large, even though they might fit in |
| // a size class. In practice this is completely fine, since the largest small |
| // size class has a single object in it already, precisely to make the transition |
| // to large objects smooth. |
| if size <= maxSmallSize-mallocHeaderSize { |
| 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 goarch.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 !raceenabled && (size < c.tinyoffset || c.tiny == 0) { |
| // Note: disabled when race detector is on, see comment near end of this function. |
| c.tiny = uintptr(x) |
| c.tinyoffset = size |
| } |
| size = maxTinySize |
| } else { |
| hasHeader := !noscan && !heapBitsInSpan(size) |
| if hasHeader { |
| size += mallocHeaderSize |
| } |
| 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(x, size) |
| } |
| if hasHeader { |
| header = (**_type)(x) |
| x = add(x, mallocHeaderSize) |
| size -= mallocHeaderSize |
| } |
| } |
| } else { |
| shouldhelpgc = true |
| // For large allocations, keep track of zeroed state so that |
| // bulk zeroing can be happen later in a preemptible context. |
| span = c.allocLarge(size, noscan) |
| span.freeindex = 1 |
| span.allocCount = 1 |
| size = span.elemsize |
| x = unsafe.Pointer(span.base()) |
| if needzero && span.needzero != 0 { |
| delayedZeroing = true |
| } |
| if !noscan { |
| // Tell the GC not to look at this yet. |
| span.largeType = nil |
| header = &span.largeType |
| } |
| } |
| if !noscan && !delayedZeroing { |
| c.scanAlloc += heapSetType(uintptr(x), dataSize, typ, header, span) |
| } |
| |
| // 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() |
| // As x and the heap bits are initialized, update |
| // freeIndexForScan now so x is seen by the GC |
| // (including conservative scan) as an allocated object. |
| // While this pointer can't escape into user code as a |
| // _live_ pointer until we return, conservative scanning |
| // may find a dead pointer that happens to point into this |
| // object. Delaying this update until now ensures that |
| // conservative scanning considers this pointer dead until |
| // this point. |
| span.freeIndexForScan = span.freeindex |
| |
| // 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)) |
| } |
| |
| if raceenabled { |
| racemalloc(x, size) |
| } |
| |
| if msanenabled { |
| msanmalloc(x, size) |
| } |
| |
| if asanenabled { |
| // We should only read/write the memory with the size asked by the user. |
| // The rest of the allocated memory should be poisoned, so that we can report |
| // errors when accessing poisoned memory. |
| // The allocated memory is larger than required userSize, it will also include |
| // redzone and some other padding bytes. |
| rzBeg := unsafe.Add(x, userSize) |
| asanpoison(rzBeg, size-userSize) |
| asanunpoison(x, userSize) |
| } |
| |
| // TODO(mknyszek): We should really count the header as part |
| // of gc_sys or something. The code below just pretends it is |
| // internal fragmentation and matches the GC's accounting by |
| // using the whole allocation slot. |
| fullSize := span.elemsize |
| if rate := MemProfileRate; rate > 0 { |
| // Note cache c only valid while m acquired; see #47302 |
| // |
| // N.B. Use the full size because that matches how the GC |
| // will update the mem profile on the "free" side. |
| if rate != 1 && fullSize < c.nextSample { |
| c.nextSample -= fullSize |
| } else { |
| profilealloc(mp, x, fullSize) |
| } |
| } |
| mp.mallocing = 0 |
| releasem(mp) |
| |
| // Objects can be zeroed late in a context where preemption can occur. |
| // If the object contains pointers, its pointer data must be cleared |
| // or otherwise indicate that the GC shouldn't scan it. |
| // x will keep the memory alive. |
| if delayedZeroing { |
| // N.B. size == fullSize always in this case. |
| memclrNoHeapPointersChunked(size, x) // This is a possible preemption point: see #47302 |
| |
| // Finish storing the type information for this case. |
| if !noscan { |
| mp := acquirem() |
| getMCache(mp).scanAlloc += heapSetType(uintptr(x), dataSize, typ, header, span) |
| |
| // Publish the type information with the zeroed memory. |
| publicationBarrier() |
| releasem(mp) |
| } |
| } |
| |
| if debug.malloc { |
| if inittrace.active && inittrace.id == getg().goid { |
| // Init functions are executed sequentially in a single goroutine. |
| inittrace.bytes += uint64(fullSize) |
| } |
| |
| if traceAllocFreeEnabled() { |
| trace := traceAcquire() |
| if trace.ok() { |
| trace.HeapObjectAlloc(uintptr(x), typ) |
| traceRelease(trace) |
| } |
| } |
| } |
| |
| if assistG != nil { |
| // Account for internal fragmentation in the assist |
| // debt now that we know it. |
| // |
| // N.B. Use the full size because that's how the rest |
| // of the GC accounts for bytes marked. |
| assistG.gcAssistBytes -= int64(fullSize - dataSize) |
| } |
| |
| if shouldhelpgc { |
| if t := (gcTrigger{kind: gcTriggerHeap}); t.test() { |
| gcStart(t) |
| } |
| } |
| |
| if raceenabled && noscan && dataSize < maxTinySize { |
| // Pad tinysize allocations so they are aligned with the end |
| // of the tinyalloc region. This ensures that any arithmetic |
| // that goes off the top end of the object will be detectable |
| // by checkptr (issue 38872). |
| // Note that we disable tinyalloc when raceenabled for this to work. |
| // TODO: This padding is only performed when the race detector |
| // is enabled. It would be nice to enable it if any package |
| // was compiled with checkptr, but there's no easy way to |
| // detect that (especially at compile time). |
| // TODO: enable this padding for all allocations, not just |
| // tinyalloc ones. It's tricky because of pointer maps. |
| // Maybe just all noscan objects? |
| x = add(x, size-dataSize) |
| } |
| |
| return x |
| } |
| |
| // deductAssistCredit reduces the current G's assist credit |
| // by size bytes, and assists the GC if necessary. |
| // |
| // Caller must be preemptible. |
| // |
| // Returns the G for which the assist credit was accounted. |
| func deductAssistCredit(size uintptr) *g { |
| 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) |
| } |
| } |
| return assistG |
| } |
| |
| // memclrNoHeapPointersChunked repeatedly calls memclrNoHeapPointers |
| // on chunks of the buffer to be zeroed, with opportunities for preemption |
| // along the way. memclrNoHeapPointers contains no safepoints and also |
| // cannot be preemptively scheduled, so this provides a still-efficient |
| // block copy that can also be preempted on a reasonable granularity. |
| // |
| // Use this with care; if the data being cleared is tagged to contain |
| // pointers, this allows the GC to run before it is all cleared. |
| func memclrNoHeapPointersChunked(size uintptr, x unsafe.Pointer) { |
| v := uintptr(x) |
| // got this from benchmarking. 128k is too small, 512k is too large. |
| const chunkBytes = 256 * 1024 |
| vsize := v + size |
| for voff := v; voff < vsize; voff = voff + chunkBytes { |
| if getg().preempt { |
| // may hold locks, e.g., profiling |
| goschedguarded() |
| } |
| // clear min(avail, lump) bytes |
| n := vsize - voff |
| if n > chunkBytes { |
| n = chunkBytes |
| } |
| memclrNoHeapPointers(unsafe.Pointer(voff), n) |
| } |
| } |
| |
| // 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) |
| } |
| |
| // reflect_unsafe_New is meant for package reflect, |
| // but widely used packages access it using linkname. |
| // Notable members of the hall of shame include: |
| // - gitee.com/quant1x/gox |
| // - github.com/goccy/json |
| // - github.com/modern-go/reflect2 |
| // - github.com/v2pro/plz |
| // |
| // Do not remove or change the type signature. |
| // See go.dev/issue/67401. |
| // |
| //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. |
| // |
| // newarray should be an internal detail, |
| // but widely used packages access it using linkname. |
| // Notable members of the hall of shame include: |
| // - github.com/RomiChan/protobuf |
| // - github.com/segmentio/encoding |
| // - github.com/ugorji/go/codec |
| // |
| // Do not remove or change the type signature. |
| // See go.dev/issue/67401. |
| // |
| //go:linkname newarray |
| 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) |
| } |
| |
| // reflect_unsafe_NewArray is meant for package reflect, |
| // but widely used packages access it using linkname. |
| // Notable members of the hall of shame include: |
| // - gitee.com/quant1x/gox |
| // - github.com/bytedance/sonic |
| // - github.com/goccy/json |
| // - github.com/modern-go/reflect2 |
| // - github.com/segmentio/encoding |
| // - github.com/segmentio/kafka-go |
| // - github.com/v2pro/plz |
| // |
| // Do not remove or change the type signature. |
| // See go.dev/issue/67401. |
| // |
| //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(mp) |
| if c == nil { |
| throw("profilealloc called without a P or outside bootstrapping") |
| } |
| c.nextSample = nextSample() |
| mProf_Malloc(mp, 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 gp := getg(); gp == gp.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 := cheaprandn(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(cheaprandn(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. |
| // sysStat must be non-nil. |
| // |
| // Consider marking persistentalloc'd types not in heap by embedding |
| // internal/runtime/sys.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(goarch.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 optionally 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 |
| |
| mapMemory bool // transition memory from Reserved to Ready if true |
| } |
| |
| func (l *linearAlloc) init(base, size uintptr, mapMemory bool) { |
| 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 |
| l.mapMemory = mapMemory |
| } |
| |
| 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 { |
| if l.mapMemory { |
| // Transition from Reserved to Prepared to Ready. |
| n := pEnd - l.mapped |
| sysMap(unsafe.Pointer(l.mapped), n, sysStat) |
| sysUsed(unsafe.Pointer(l.mapped), n, n) |
| } |
| 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 which embed |
| // internal/runtime/sys.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? |
| type notInHeap struct{ _ sys.NotInHeap } |
| |
| func (p *notInHeap) add(bytes uintptr) *notInHeap { |
| return (*notInHeap)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + bytes)) |
| } |
| |
| // computeRZlog computes the size of the redzone. |
| // Refer to the implementation of the compiler-rt. |
| func computeRZlog(userSize uintptr) uintptr { |
| switch { |
| case userSize <= (64 - 16): |
| return 16 << 0 |
| case userSize <= (128 - 32): |
| return 16 << 1 |
| case userSize <= (512 - 64): |
| return 16 << 2 |
| case userSize <= (4096 - 128): |
| return 16 << 3 |
| case userSize <= (1<<14)-256: |
| return 16 << 4 |
| case userSize <= (1<<15)-512: |
| return 16 << 5 |
| case userSize <= (1<<16)-1024: |
| return 16 << 6 |
| default: |
| return 16 << 7 |
| } |
| } |