[dev.garbage] all: merge dev.cc into dev.garbage

[gostls13.git] / src / runtime / malloc2.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package runtime

import "unsafe"

// Memory allocator, based on tcmalloc.
// 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 100 size classes, each of which
// has its own free list 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 free list
// allocators.
//
// The allocator's data structures are:
//
//      FixAlloc: a free-list allocator for fixed-size objects,
//              used to manage storage used by the allocator.
//      MHeap: the malloc heap, managed at page (4096-byte) granularity.
//      MSpan: a run of pages managed by the MHeap.
//      MCentral: a shared free list for a given size class.
//      MCache: a per-thread (in Go, per-P) cache for small objects.
//      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 MCache free list.
//         If the list is not empty, allocate an object from it.
//         This can all be done without acquiring a lock.
//
//      2. If the MCache free list is empty, replenish it by
//         taking a bunch of objects from the MCentral free list.
//         Moving a bunch amortizes the cost of acquiring the MCentral lock.
//
//      3. If the MCentral free list is empty, replenish it by
//         allocating a run of pages from the MHeap and then
//         chopping that memory into a objects of the given size.
//         Allocating many objects amortizes the cost of locking
//         the heap.
//
//      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.
//
// Freeing a small object proceeds up the same hierarchy:
//
//      1. Look up the size class for the object and add it to
//         the MCache free list.
//
//      2. If the MCache free list is too long or the MCache has
//         too much memory, return some to the MCentral free lists.
//
//      3. If all the objects in a given span have returned to
//         the MCentral list, return that span to the page heap.
//
//      4. If the heap has too much memory, return some to the
//         operating system.
//
//      TODO(rsc): Step 4 is not implemented.
//
// Allocating and freeing a large object uses the page heap
// directly, bypassing the MCache and MCentral free lists.
//
// The small objects on the MCache and MCentral free lists
// may or may not be zeroed.  They are zeroed if and only if
// the second word of the object is zero.  A span in the
// page heap is zeroed unless s->needzero is set. When a span
// is allocated to break into small objects, it is zeroed if needed
// and s->needzero is set. There are two main benefits to delaying the
// zeroing this way:
//
//      1. stack frames allocated from the small object lists
//         or the page heap can avoid zeroing altogether.
//      2. the cost of zeroing when reusing a small object is
//         charged to the mutator, not the garbage collector.
//
// This C code was written with an eye toward translating to Go
// in the future.  Methods have the form Type_Method(Type *t, ...).

const (
        _PageShift = 13
        _PageSize  = 1 << _PageShift
        _PageMask  = _PageSize - 1
)

const (
        // _64bit = 1 on 64-bit systems, 0 on 32-bit systems
        _64bit = 1 << (^uintptr(0) >> 63) / 2

        // Computed constant.  The definition of MaxSmallSize and the
        // algorithm in msize.c produce some number of different allocation
        // size classes.  NumSizeClasses is that number.  It's needed here
        // because there are static arrays of this length; when msize runs its
        // size choosing algorithm it double-checks that NumSizeClasses agrees.
        _NumSizeClasses = 67

        // Tunable constants.
        _MaxSmallSize = 32 << 10

        // Tiny allocator parameters, see "Tiny allocator" comment in malloc.goc.
        _TinySize      = 16
        _TinySizeClass = 2

        _FixAllocChunk  = 16 << 10               // Chunk size for FixAlloc
        _MaxMHeapList   = 1 << (20 - _PageShift) // Maximum page length for fixed-size list in MHeap.
        _HeapAllocChunk = 1 << 20                // Chunk size for heap growth

        // 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.
        _NumStackOrders = 3

        // Number of bits in page to span calculations (4k pages).
        // On Windows 64-bit we limit the arena to 32GB or 35 bits.
        // Windows counts memory used by page table into committed memory
        // of the process, so we can't reserve too much memory.
        // See http://golang.org/issue/5402 and http://golang.org/issue/5236.
        // On other 64-bit platforms, we limit the arena to 128GB, or 37 bits.
        // On 32-bit, we don't bother limiting anything, so we use the full 32-bit address.
        _MHeapMap_TotalBits = (_64bit*_Windows)*35 + (_64bit*(1-_Windows))*37 + (1-_64bit)*32
        _MHeapMap_Bits      = _MHeapMap_TotalBits - _PageShift

        _MaxMem = uintptr(1<<_MHeapMap_TotalBits - 1)

        // 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
)

// A generic linked list of blocks.  (Typically the block is bigger than sizeof(MLink).)
type mlink struct {
        next *mlink
}

// sysAlloc obtains a large chunk of zeroed memory from the
// operating system, typically on the order of a hundred kilobytes
// or a megabyte.
// NOTE: sysAlloc returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysUnused notifies the operating system that the contents
// of the memory region are no longer needed and can be reused
// for other purposes.
// SysUsed notifies the operating system that the contents
// of the memory region are needed again.
//
// SysFree returns it unconditionally; this is only used if
// an out-of-memory error has been detected midway through
// an allocation.  It is okay if SysFree is a no-op.
//
// SysReserve reserves address space without allocating memory.
// If the pointer passed to it is non-nil, the caller wants the
// reservation there, but SysReserve can still choose another
// location if that one is unavailable.  On some systems and in some
// cases SysReserve will simply check that the address space is
// available and not actually reserve it.  If SysReserve returns
// non-nil, it sets *reserved to true if the address space is
// reserved, false if it has merely been checked.
// NOTE: SysReserve returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysMap maps previously reserved address space for use.
// The reserved argument is true if the address space was really
// reserved, not merely checked.
//
// SysFault marks a (already sysAlloc'd) region to fault
// if accessed.  Used only for debugging the runtime.

// FixAlloc is a simple free-list allocator for fixed size objects.
// Malloc uses a FixAlloc wrapped around sysAlloc to manages its
// MCache and MSpan objects.
//
// Memory returned by FixAlloc_Alloc is not zeroed.
// The caller is responsible for locking around FixAlloc calls.
// Callers can keep state in the object but the first word is
// smashed by freeing and reallocating.
type fixalloc struct {
        size   uintptr
        first  unsafe.Pointer // go func(unsafe.pointer, unsafe.pointer); f(arg, p) called first time p is returned
        arg    unsafe.Pointer
        list   *mlink
        chunk  *byte
        nchunk uint32
        inuse  uintptr // in-use bytes now
        stat   *uint64
}

// Statistics.
// Shared with Go: if you edit this structure, also edit type MemStats in mem.go.
type mstats struct {
        // General statistics.
        alloc       uint64 // bytes allocated and still in use
        total_alloc uint64 // bytes allocated (even if freed)
        sys         uint64 // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
        nlookup     uint64 // number of pointer lookups
        nmalloc     uint64 // number of mallocs
        nfree       uint64 // number of frees

        // Statistics about malloc heap.
        // protected by mheap.lock
        heap_alloc    uint64 // bytes allocated and still in use
        heap_sys      uint64 // bytes obtained from system
        heap_idle     uint64 // bytes in idle spans
        heap_inuse    uint64 // bytes in non-idle spans
        heap_released uint64 // bytes released to the os
        heap_objects  uint64 // total number of allocated objects

        // Statistics about allocation of low-level fixed-size structures.
        // Protected by FixAlloc locks.
        stacks_inuse uint64 // this number is included in heap_inuse above
        stacks_sys   uint64 // always 0 in mstats
        mspan_inuse  uint64 // mspan structures
        mspan_sys    uint64
        mcache_inuse uint64 // mcache structures
        mcache_sys   uint64
        buckhash_sys uint64 // profiling bucket hash table
        gc_sys       uint64
        other_sys    uint64

        // Statistics about garbage collector.
        // Protected by mheap or stopping the world during GC.
        next_gc        uint64 // next gc (in heap_alloc time)
        last_gc        uint64 // last gc (in absolute time)
        pause_total_ns uint64
        pause_ns       [256]uint64 // circular buffer of recent gc pause lengths
        pause_end      [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970)
        numgc          uint32
        enablegc       bool
        debuggc        bool

        // Statistics about allocation size classes.

        by_size [_NumSizeClasses]struct {
                size    uint32
                nmalloc uint64
                nfree   uint64
        }

        tinyallocs uint64 // number of tiny allocations that didn't cause actual allocation; not exported to go directly
}

var memstats mstats

// Size classes.  Computed and initialized by InitSizes.
//
// SizeToClass(0 <= n <= MaxSmallSize) returns the size class,
//      1 <= sizeclass < NumSizeClasses, for n.
//      Size class 0 is reserved to mean "not small".
//
// class_to_size[i] = largest size in class i
// class_to_allocnpages[i] = number of pages to allocate when
//      making new objects in class i

var class_to_size [_NumSizeClasses]int32
var class_to_allocnpages [_NumSizeClasses]int32
var size_to_class8 [1024/8 + 1]int8
var size_to_class128 [(_MaxSmallSize-1024)/128 + 1]int8

type mcachelist struct {
        list  *mlink
        nlist uint32
}

type stackfreelist struct {
        list *mlink  // linked list of free stacks
        size uintptr // total size of stacks in list
}

// Per-thread (in Go, per-P) cache for small objects.
// No locking needed because it is per-thread (per-P).
type mcache struct {
        // The following members are accessed on every malloc,
        // so they are grouped here for better caching.
        next_sample      int32  // trigger heap sample after allocating this many bytes
        local_cachealloc intptr // bytes allocated (or freed) from cache since last lock of heap
        // Allocator cache for tiny objects w/o pointers.
        // See "Tiny allocator" comment in malloc.goc.
        tiny             *byte
        tinysize         uintptr
        local_tinyallocs uintptr // number of tiny allocs not counted in other stats

        // The rest is not accessed on every malloc.
        alloc [_NumSizeClasses]*mspan // spans to allocate from

        stackcache [_NumStackOrders]stackfreelist

        sudogcache *sudog

        // Local allocator stats, flushed during GC.
        local_nlookup    uintptr                  // number of pointer lookups
        local_largefree  uintptr                  // bytes freed for large objects (>maxsmallsize)
        local_nlargefree uintptr                  // number of frees for large objects (>maxsmallsize)
        local_nsmallfree [_NumSizeClasses]uintptr // number of frees for small objects (<=maxsmallsize)
}

const (
        _KindSpecialFinalizer = 1
        _KindSpecialProfile   = 2
        // Note: The finalizer special must be first because if we're freeing
        // an object, a finalizer special will cause the freeing operation
        // to abort, and we want to keep the other special records around
        // if that happens.
)

type special struct {
        next   *special // linked list in span
        offset uint16   // span offset of object
        kind   byte     // kind of special
}

// The described object has a finalizer set for it.
type specialfinalizer struct {
        special special
        fn      *funcval
        nret    uintptr
        fint    *_type
        ot      *ptrtype
}

// The described object is being heap profiled.
type specialprofile struct {
        special special
        b       *bucket
}

// An MSpan is a run of pages.
const (
        _MSpanInUse = iota // allocated for garbage collected heap
        _MSpanStack        // allocated for use by stack allocator
        _MSpanFree
        _MSpanListHead
        _MSpanDead
)

type mspan struct {
        next     *mspan  // in a span linked list
        prev     *mspan  // in a span linked list
        start    pageID  // starting page number
        npages   uintptr // number of pages in span
        freelist *mlink  // list of free objects
        // sweep generation:
        // if sweepgen == h->sweepgen - 2, the span needs sweeping
        // if sweepgen == h->sweepgen - 1, the span is currently being swept
        // if sweepgen == h->sweepgen, the span is swept and ready to use
        // h->sweepgen is incremented by 2 after every GC
        sweepgen    uint32
        ref         uint16   // capacity - number of objects in freelist
        sizeclass   uint8    // size class
        incache     bool     // being used by an mcache
        state       uint8    // mspaninuse etc
        needzero    uint8    // needs to be zeroed before allocation
        elemsize    uintptr  // computed from sizeclass or from npages
        unusedsince int64    // first time spotted by gc in mspanfree state
        npreleased  uintptr  // number of pages released to the os
        limit       uintptr  // end of data in span
        speciallock mutex    // guards specials list
        specials    *special // linked list of special records sorted by offset.
}

// Every MSpan is in one doubly-linked list,
// either one of the MHeap's free lists or one of the
// MCentral's span lists.  We use empty MSpan structures as list heads.

// Central list of free objects of a given size.
type mcentral struct {
        lock      mutex
        sizeclass int32
        nonempty  mspan // list of spans with a free object
        empty     mspan // list of spans with no free objects (or cached in an mcache)
}

// Main malloc heap.
// The heap itself is the "free[]" and "large" arrays,
// but all the other global data is here too.
type mheap struct {
        lock      mutex
        free      [_MaxMHeapList]mspan // free lists of given length
        freelarge mspan                // free lists length >= _MaxMHeapList
        busy      [_MaxMHeapList]mspan // busy lists of large objects of given length
        busylarge mspan                // busy lists of large objects length >= _MaxMHeapList
        allspans  **mspan              // all spans out there
        gcspans   **mspan              // copy of allspans referenced by gc marker or sweeper
        nspan     uint32
        sweepgen  uint32 // sweep generation, see comment in mspan
        sweepdone uint32 // all spans are swept

        // span lookup
        spans        **mspan
        spans_mapped uintptr

        // range of addresses we might see in the heap
        bitmap         uintptr
        bitmap_mapped  uintptr
        arena_start    uintptr
        arena_used     uintptr
        arena_end      uintptr
        arena_reserved bool

        // central free lists for small size classes.
        // the padding makes sure that the MCentrals are
        // spaced CacheLineSize bytes apart, so that each MCentral.lock
        // gets its own cache line.
        central [_NumSizeClasses]struct {
                mcentral mcentral
                pad      [_CacheLineSize]byte
        }

        spanalloc             fixalloc // allocator for span*
        cachealloc            fixalloc // allocator for mcache*
        specialfinalizeralloc fixalloc // allocator for specialfinalizer*
        specialprofilealloc   fixalloc // allocator for specialprofile*
        speciallock           mutex    // lock for sepcial record allocators.

        // Malloc stats.
        largefree  uint64                  // bytes freed for large objects (>maxsmallsize)
        nlargefree uint64                  // number of frees for large objects (>maxsmallsize)
        nsmallfree [_NumSizeClasses]uint64 // number of frees for small objects (<=maxsmallsize)
}

var mheap_ mheap

const (
        // flags to malloc
        _FlagNoScan = 1 << 0 // GC doesn't have to scan object
        _FlagNoZero = 1 << 1 // don't zero memory
)

// NOTE: Layout known to queuefinalizer.
type finalizer struct {
        fn   *funcval       // function to call
        arg  unsafe.Pointer // ptr to object
        nret uintptr        // bytes of return values from fn
        fint *_type         // type of first argument of fn
        ot   *ptrtype       // type of ptr to object
}

type finblock struct {
        alllink *finblock
        next    *finblock
        cnt     int32
        cap     int32
        fin     [1]finalizer
}

// Information from the compiler about the layout of stack frames.
type bitvector struct {
        n        int32 // # of bits
        bytedata *uint8
}

type stackmap struct {
        n        int32   // number of bitmaps
        nbit     int32   // number of bits in each bitmap
        bytedata [0]byte // bitmaps, each starting on a 32-bit boundary
}

// Returns pointer map data for the given stackmap index
// (the index is encoded in PCDATA_StackMapIndex).

// defined in mgc0.go