2011-10-08 Paul Thomas <pault@gcc.gnu.org>

[official-gcc.git] / libgo / runtime / malloc.h

// 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.

// 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-M) 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.  The spans in the
// page heap are always zeroed.  When a span full of objects
// is returned to the page heap, the objects that need to be
// are zeroed first.  There are two main benefits to delaying the
// zeroing this way:
//
//      1. stack frames allocated from the small object lists
//         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, ...).

typedef struct MCentral MCentral;
typedef struct MHeap    MHeap;
typedef struct MSpan    MSpan;
typedef struct MStats   MStats;
typedef struct MLink    MLink;

enum
{
        PageShift       = 12,
        PageSize        = 1<<PageShift,
        PageMask        = PageSize - 1,
};
typedef uintptr PageID;         // address >> PageShift

enum
{
        // 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 = 61,

        // Tunable constants.
        MaxSmallSize = 32<<10,

        FixAllocChunk = 128<<10,        // Chunk size for FixAlloc
        MaxMCacheListLen = 256,         // Maximum objects on MCacheList
        MaxMCacheSize = 2<<20,          // Maximum bytes in one MCache
        MaxMHeapList = 1<<(20 - PageShift),     // Maximum page length for fixed-size list in MHeap.
        HeapAllocChunk = 1<<20,         // Chunk size for heap growth

        // Number of bits in page to span calculations (4k pages).
        // On 64-bit, we limit the arena to 16G, so 22 bits suffices.
        // On 32-bit, we don't bother limiting anything: 20 bits for 4G.
#if __SIZEOF_POINTER__ == 8
        MHeapMap_Bits = 22,
#else
        MHeapMap_Bits = 20,
#endif
};

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

// SysAlloc obtains a large chunk of zeroed memory from the
// operating system, typically on the order of a hundred kilobytes
// or a megabyte.  If the pointer argument is non-nil, the caller
// wants a mapping there or nowhere.
//
// SysUnused notifies the operating system that the contents
// of the memory region are no longer needed and can be reused
// for other purposes.  The program reserves the right to start
// accessing those pages in the future.
//
// 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.
//
// SysMap maps previously reserved address space for use.

void*   runtime_SysAlloc(uintptr nbytes);
void    runtime_SysFree(void *v, uintptr nbytes);
void    runtime_SysUnused(void *v, uintptr nbytes);
void    runtime_SysMap(void *v, uintptr nbytes);
void*   runtime_SysReserve(void *v, uintptr nbytes);

// 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.
struct FixAlloc
{
        uintptr size;
        void *(*alloc)(uintptr);
        void (*first)(void *arg, byte *p);      // called first time p is returned
        void *arg;
        MLink *list;
        byte *chunk;
        uint32 nchunk;
        uintptr inuse;  // in-use bytes now
        uintptr sys;    // bytes obtained from system
};

void    runtime_FixAlloc_Init(FixAlloc *f, uintptr size, void *(*alloc)(uintptr), void (*first)(void*, byte*), void *arg);
void*   runtime_FixAlloc_Alloc(FixAlloc *f);
void    runtime_FixAlloc_Free(FixAlloc *f, void *p);


// Statistics.
// Shared with Go: if you edit this structure, also edit extern.go.
struct MStats
{
        // General statistics.
        uint64  alloc;          // bytes allocated and still in use
        uint64  total_alloc;    // bytes allocated (even if freed)
        uint64  sys;            // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
        uint64  nlookup;        // number of pointer lookups
        uint64  nmalloc;        // number of mallocs
        uint64  nfree;  // number of frees
        
        // Statistics about malloc heap.
        // protected by mheap.Lock
        uint64  heap_alloc;     // bytes allocated and still in use
        uint64  heap_sys;       // bytes obtained from system
        uint64  heap_idle;      // bytes in idle spans
        uint64  heap_inuse;     // bytes in non-idle spans
        uint64  heap_objects;   // total number of allocated objects

        // Statistics about allocation of low-level fixed-size structures.
        // Protected by FixAlloc locks.
        uint64  stacks_inuse;   // bootstrap stacks
        uint64  stacks_sys;
        uint64  mspan_inuse;    // MSpan structures
        uint64  mspan_sys;
        uint64  mcache_inuse;   // MCache structures
        uint64  mcache_sys;
        uint64  buckhash_sys;   // profiling bucket hash table
        
        // Statistics about garbage collector.
        // Protected by stopping the world during GC.
        uint64  next_gc;        // next GC (in heap_alloc time)
        uint64  pause_total_ns;
        uint64  pause_ns[256];
        uint32  numgc;
        bool    enablegc;
        bool    debuggc;
        
        // Statistics about allocation size classes.
        struct {
                uint32 size;
                uint64 nmalloc;
                uint64 nfree;
        } by_size[NumSizeClasses];
};

extern MStats mstats
  __asm__ ("libgo_runtime.runtime.MemStats");


// 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
// class_to_transfercount[i] = number of objects to move when
//      taking a bunch of objects out of the central lists
//      and putting them in the thread free list.

int32   runtime_SizeToClass(int32);
extern  int32   runtime_class_to_size[NumSizeClasses];
extern  int32   runtime_class_to_allocnpages[NumSizeClasses];
extern  int32   runtime_class_to_transfercount[NumSizeClasses];
extern  void    runtime_InitSizes(void);


// Per-thread (in Go, per-M) cache for small objects.
// No locking needed because it is per-thread (per-M).
typedef struct MCacheList MCacheList;
struct MCacheList
{
        MLink *list;
        uint32 nlist;
        uint32 nlistmin;
};

struct MCache
{
        MCacheList list[NumSizeClasses];
        uint64 size;
        int64 local_cachealloc; // bytes allocated (or freed) from cache since last lock of heap
        int64 local_objects;    // objects allocated (or freed) from cache since last lock of heap
        int64 local_alloc;      // bytes allocated (or freed) since last lock of heap
        int64 local_total_alloc;        // bytes allocated (even if freed) since last lock of heap
        int64 local_nmalloc;    // number of mallocs since last lock of heap
        int64 local_nfree;      // number of frees since last lock of heap
        int64 local_nlookup;    // number of pointer lookups since last lock of heap
        int32 next_sample;      // trigger heap sample after allocating this many bytes
        // Statistics about allocation size classes since last lock of heap
        struct {
                int64 nmalloc;
                int64 nfree;
        } local_by_size[NumSizeClasses];
        
};

void*   runtime_MCache_Alloc(MCache *c, int32 sizeclass, uintptr size, int32 zeroed);
void    runtime_MCache_Free(MCache *c, void *p, int32 sizeclass, uintptr size);
void    runtime_MCache_ReleaseAll(MCache *c);

// An MSpan is a run of pages.
enum
{
        MSpanInUse = 0,
        MSpanFree,
        MSpanListHead,
        MSpanDead,
};
struct MSpan
{
        MSpan   *next;          // in a span linked list
        MSpan   *prev;          // in a span linked list
        MSpan   *allnext;               // in the list of all spans
        PageID  start;          // starting page number
        uintptr npages;         // number of pages in span
        MLink   *freelist;      // list of free objects
        uint32  ref;            // number of allocated objects in this span
        uint32  sizeclass;      // size class
        uint32  state;          // MSpanInUse etc
        byte    *limit; // end of data in span
};

void    runtime_MSpan_Init(MSpan *span, PageID start, uintptr npages);

// 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.
void    runtime_MSpanList_Init(MSpan *list);
bool    runtime_MSpanList_IsEmpty(MSpan *list);
void    runtime_MSpanList_Insert(MSpan *list, MSpan *span);
void    runtime_MSpanList_Remove(MSpan *span);  // from whatever list it is in


// Central list of free objects of a given size.
struct MCentral
{
        Lock;
        int32 sizeclass;
        MSpan nonempty;
        MSpan empty;
        int32 nfree;
};

void    runtime_MCentral_Init(MCentral *c, int32 sizeclass);
int32   runtime_MCentral_AllocList(MCentral *c, int32 n, MLink **first);
void    runtime_MCentral_FreeList(MCentral *c, int32 n, MLink *first);

// Main malloc heap.
// The heap itself is the "free[]" and "large" arrays,
// but all the other global data is here too.
struct MHeap
{
        Lock;
        MSpan free[MaxMHeapList];       // free lists of given length
        MSpan large;                    // free lists length >= MaxMHeapList
        MSpan *allspans;

        // span lookup
        MSpan *map[1<<MHeapMap_Bits];

        // range of addresses we might see in the heap
        byte *bitmap;
        uintptr bitmap_mapped;
        byte *arena_start;
        byte *arena_used;
        byte *arena_end;
        
        // central free lists for small size classes.
        // the union makes sure that the MCentrals are
        // spaced 64 bytes apart, so that each MCentral.Lock
        // gets its own cache line.
        union {
                MCentral;
                byte pad[64];
        } central[NumSizeClasses];

        FixAlloc spanalloc;     // allocator for Span*
        FixAlloc cachealloc;    // allocator for MCache*
};
extern MHeap runtime_mheap;

void    runtime_MHeap_Init(MHeap *h, void *(*allocator)(uintptr));
MSpan*  runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, int32 acct);
void    runtime_MHeap_Free(MHeap *h, MSpan *s, int32 acct);
MSpan*  runtime_MHeap_Lookup(MHeap *h, void *v);
MSpan*  runtime_MHeap_LookupMaybe(MHeap *h, void *v);
void    runtime_MGetSizeClassInfo(int32 sizeclass, uintptr *size, int32 *npages, int32 *nobj);
void*   runtime_MHeap_SysAlloc(MHeap *h, uintptr n);
void    runtime_MHeap_MapBits(MHeap *h);

void*   runtime_mallocgc(uintptr size, uint32 flag, int32 dogc, int32 zeroed);
int32   runtime_mlookup(void *v, byte **base, uintptr *size, MSpan **s);
void    runtime_gc(int32 force);
void    runtime_markallocated(void *v, uintptr n, bool noptr);
void    runtime_checkallocated(void *v, uintptr n);
void    runtime_markfreed(void *v, uintptr n);
void    runtime_checkfreed(void *v, uintptr n);
int32   runtime_checking;
void    runtime_markspan(void *v, uintptr size, uintptr n, bool leftover);
void    runtime_unmarkspan(void *v, uintptr size);
bool    runtime_blockspecial(void*);
void    runtime_setblockspecial(void*);
void    runtime_purgecachedstats(M*);

enum
{
        // flags to malloc
        FlagNoPointers = 1<<0,  // no pointers here
        FlagNoProfiling = 1<<1, // must not profile
        FlagNoGC = 1<<2,        // must not free or scan for pointers
};

void    runtime_Mprof_Init(void);
void    runtime_MProf_Malloc(void*, uintptr);
void    runtime_MProf_Free(void*, uintptr);
void    runtime_MProf_Mark(void (*scan)(byte *, int64));

// Malloc profiling settings.
// Must match definition in extern.go.
enum {
        MProf_None = 0,
        MProf_Sample = 1,
        MProf_All = 2,
};
extern int32 runtime_malloc_profile;

typedef struct Finalizer Finalizer;
struct Finalizer
{
        Finalizer *next;        // for use by caller of getfinalizer
        void (*fn)(void*);
        void *arg;
        const struct __go_func_type *ft;
};

Finalizer*      runtime_getfinalizer(void*, bool);