2014-07-29 Ed Smith-Rowland <3dw4rd@verizon.net>

[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-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, ...).

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

enum
{
        PageShift       = 13,
        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 = 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

        // Number of bits in page to span calculations (4k pages).
        // On Windows 64-bit we limit the arena to 32GB or 35 bits (see below for reason).
        // 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.
#if __SIZEOF_POINTER__ == 8
#ifdef GOOS_windows
        // 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.
        MHeapMap_Bits = 35 - PageShift,
#else
        MHeapMap_Bits = 37 - PageShift,
#endif
#else
        MHeapMap_Bits = 32 - PageShift,
#endif

        // 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 8 cpus.
        MaxGcproc = 8,
};

// Maximum memory allocation size, a hint for callers.
// This must be a #define instead of an enum because it
// is so large.
#if __SIZEOF_POINTER__ == 8
#define MaxMem  (1ULL<<(MHeapMap_Bits+PageShift))       /* 128 GB or 32 GB */
#else
#define MaxMem  ((uintptr)-1)
#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.
// 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.

void*   runtime_SysAlloc(uintptr nbytes, uint64 *stat);
void    runtime_SysFree(void *v, uintptr nbytes, uint64 *stat);
void    runtime_SysUnused(void *v, uintptr nbytes);
void    runtime_SysUsed(void *v, uintptr nbytes);
void    runtime_SysMap(void *v, uintptr nbytes, bool reserved, uint64 *stat);
void*   runtime_SysReserve(void *v, uintptr nbytes, bool *reserved);
void    runtime_SysFault(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    (*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
        uint64* stat;
};

void    runtime_FixAlloc_Init(FixAlloc *f, uintptr size, void (*first)(void*, byte*), void *arg, uint64 *stat);
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 type MemStats in mem.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_released;  // bytes released to the OS
        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
        uint64  gc_sys;
        uint64  other_sys;

        // Statistics about garbage collector.
        // Protected by mheap or stopping the world during GC.
        uint64  next_gc;        // next GC (in heap_alloc time)
        uint64  last_gc;        // last GC (in absolute 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__ (GOSYM_PREFIX "runtime.memStats");
void    runtime_updatememstats(GCStats *stats);

// 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

int32   runtime_SizeToClass(int32);
uintptr runtime_roundupsize(uintptr);
extern  int32   runtime_class_to_size[NumSizeClasses];
extern  int32   runtime_class_to_allocnpages[NumSizeClasses];
extern  int8    runtime_size_to_class8[1024/8 + 1];
extern  int8    runtime_size_to_class128[(MaxSmallSize-1024)/128 + 1];
extern  void    runtime_InitSizes(void);


typedef struct MCacheList MCacheList;
struct MCacheList
{
        MLink *list;
        uint32 nlist;
};

// Per-thread (in Go, per-P) cache for small objects.
// No locking needed because it is per-thread (per-P).
struct MCache
{
        // The following members are accessed on every malloc,
        // so they are grouped here for better caching.
        int32 next_sample;              // trigger heap sample after allocating this many bytes
        intptr local_cachealloc;        // 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.
        byte*   tiny;
        uintptr tinysize;
        // The rest is not accessed on every malloc.
        MSpan*  alloc[NumSizeClasses];  // spans to allocate from
        MCacheList free[NumSizeClasses];// lists of explicitly freed objects
        // Local allocator stats, flushed during GC.
        uintptr local_nlookup;          // number of pointer lookups
        uintptr local_largefree;        // bytes freed for large objects (>MaxSmallSize)
        uintptr local_nlargefree;       // number of frees for large objects (>MaxSmallSize)
        uintptr local_nsmallfree[NumSizeClasses];       // number of frees for small objects (<=MaxSmallSize)
};

MSpan*  runtime_MCache_Refill(MCache *c, int32 sizeclass);
void    runtime_MCache_Free(MCache *c, MLink *p, int32 sizeclass, uintptr size);
void    runtime_MCache_ReleaseAll(MCache *c);

// MTypes describes the types of blocks allocated within a span.
// The compression field describes the layout of the data.
//
// MTypes_Empty:
//     All blocks are free, or no type information is available for
//     allocated blocks.
//     The data field has no meaning.
// MTypes_Single:
//     The span contains just one block.
//     The data field holds the type information.
//     The sysalloc field has no meaning.
// MTypes_Words:
//     The span contains multiple blocks.
//     The data field points to an array of type [NumBlocks]uintptr,
//     and each element of the array holds the type of the corresponding
//     block.
// MTypes_Bytes:
//     The span contains at most seven different types of blocks.
//     The data field points to the following structure:
//         struct {
//             type  [8]uintptr       // type[0] is always 0
//             index [NumBlocks]byte
//         }
//     The type of the i-th block is: data.type[data.index[i]]
enum
{
        MTypes_Empty = 0,
        MTypes_Single = 1,
        MTypes_Words = 2,
        MTypes_Bytes = 3,
};
struct MTypes
{
        byte    compression;    // one of MTypes_*
        uintptr data;
};

enum
{
        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.
};

typedef struct Special Special;
struct Special
{
        Special*        next;   // linked list in span
        uint16          offset; // span offset of object
        byte            kind;   // kind of Special
};

// The described object has a finalizer set for it.
typedef struct SpecialFinalizer SpecialFinalizer;
struct SpecialFinalizer
{
        Special;
        FuncVal*        fn;
        const FuncType* ft;
        const PtrType*  ot;
};

// The described object is being heap profiled.
typedef struct Bucket Bucket; // from mprof.goc
typedef struct SpecialProfile SpecialProfile;
struct SpecialProfile
{
        Special;
        Bucket* b;
};

// 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
        PageID  start;          // starting page number
        uintptr npages;         // number of pages in span
        MLink   *freelist;      // 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
        uint32  sweepgen;
        uint16  ref;            // capacity - number of objects in freelist
        uint8   sizeclass;      // size class
        bool    incache;        // being used by an MCache
        uint8   state;          // MSpanInUse etc
        uint8   needzero;       // needs to be zeroed before allocation
        uintptr elemsize;       // computed from sizeclass or from npages
        int64   unusedsince;    // First time spotted by GC in MSpanFree state
        uintptr npreleased;     // number of pages released to the OS
        byte    *limit;         // end of data in span
        MTypes  types;          // types of allocated objects in this span
        Lock    specialLock;    // guards specials list
        Special *specials;      // linked list of special records sorted by offset.
        MLink   *freebuf;       // objects freed explicitly, not incorporated into freelist yet
};

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

// 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_InsertBack(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; // list of spans with a free object
        MSpan empty;    // list of spans with no free objects (or cached in an MCache)
        int32 nfree;    // # of objects available in nonempty spans
};

void    runtime_MCentral_Init(MCentral *c, int32 sizeclass);
MSpan*  runtime_MCentral_CacheSpan(MCentral *c);
void    runtime_MCentral_UncacheSpan(MCentral *c, MSpan *s);
bool    runtime_MCentral_FreeSpan(MCentral *c, MSpan *s, int32 n, MLink *start, MLink *end);
void    runtime_MCentral_FreeList(MCentral *c, MLink *start); // TODO: need this?

// 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 freelarge;                // free lists length >= MaxMHeapList
        MSpan busy[MaxMHeapList];       // busy lists of large objects of given length
        MSpan busylarge;                // busy lists of large objects length >= MaxMHeapList
        MSpan **allspans;               // all spans out there
        MSpan **sweepspans;             // copy of allspans referenced by sweeper
        uint32  nspan;
        uint32  nspancap;
        uint32  sweepgen;               // sweep generation, see comment in MSpan
        uint32  sweepdone;              // all spans are swept

        // span lookup
        MSpan** spans;
        uintptr spans_mapped;

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

        // 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.
        struct {
                MCentral;
                byte pad[64];
        } central[NumSizeClasses];

        FixAlloc spanalloc;     // allocator for Span*
        FixAlloc cachealloc;    // allocator for MCache*
        FixAlloc specialfinalizeralloc; // allocator for SpecialFinalizer*
        FixAlloc specialprofilealloc;   // allocator for SpecialProfile*
        Lock speciallock; // lock for sepcial record allocators.

        // Malloc stats.
        uint64 largefree;       // bytes freed for large objects (>MaxSmallSize)
        uint64 nlargefree;      // number of frees for large objects (>MaxSmallSize)
        uint64 nsmallfree[NumSizeClasses];      // number of frees for small objects (<=MaxSmallSize)
};
extern MHeap runtime_mheap;

void    runtime_MHeap_Init(MHeap *h);
MSpan*  runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, bool large, bool needzero);
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_MHeap_MapSpans(MHeap *h);
void    runtime_MHeap_Scavenger(void*);
void    runtime_MHeap_SplitSpan(MHeap *h, MSpan *s);

void*   runtime_mallocgc(uintptr size, uintptr typ, uint32 flag);
void*   runtime_persistentalloc(uintptr size, uintptr align, uint64 *stat);
int32   runtime_mlookup(void *v, byte **base, uintptr *size, MSpan **s);
void    runtime_gc(int32 force);
uintptr runtime_sweepone(void);
void    runtime_markscan(void *v);
void    runtime_marknogc(void *v);
void    runtime_checkallocated(void *v, uintptr n);
void    runtime_markfreed(void *v);
void    runtime_checkfreed(void *v, uintptr n);
extern  int32   runtime_checking;
void    runtime_markspan(void *v, uintptr size, uintptr n, bool leftover);
void    runtime_unmarkspan(void *v, uintptr size);
void    runtime_purgecachedstats(MCache*);
void*   runtime_cnew(const Type*);
void*   runtime_cnewarray(const Type*, intgo);
void    runtime_tracealloc(void*, uintptr, uintptr);
void    runtime_tracefree(void*, uintptr);
void    runtime_tracegc(void);

uintptr runtime_gettype(void*);

enum
{
        // flags to malloc
        FlagNoScan      = 1<<0, // GC doesn't have to scan object
        FlagNoProfiling = 1<<1, // must not profile
        FlagNoGC        = 1<<2, // must not free or scan for pointers
        FlagNoZero      = 1<<3, // don't zero memory
        FlagNoInvokeGC  = 1<<4, // don't invoke GC
};

typedef struct Obj Obj;
struct Obj
{
        byte    *p;     // data pointer
        uintptr n;      // size of data in bytes
        uintptr ti;     // type info
};

void    runtime_MProf_Malloc(void*, uintptr);
void    runtime_MProf_Free(Bucket*, uintptr, bool);
void    runtime_MProf_GC(void);
void    runtime_iterate_memprof(void (*callback)(Bucket*, uintptr, Location*, uintptr, uintptr, uintptr));
int32   runtime_gcprocs(void);
void    runtime_helpgc(int32 nproc);
void    runtime_gchelper(void);
void    runtime_createfing(void);
G*      runtime_wakefing(void);
extern bool     runtime_fingwait;
extern bool     runtime_fingwake;

void    runtime_setprofilebucket(void *p, Bucket *b);

struct __go_func_type;
struct __go_ptr_type;
bool    runtime_addfinalizer(void *p, FuncVal *fn, const struct __go_func_type*, const struct __go_ptr_type*);
void    runtime_removefinalizer(void*);
void    runtime_queuefinalizer(void *p, FuncVal *fn, const struct __go_func_type *ft, const struct __go_ptr_type *ot);

void    runtime_freeallspecials(MSpan *span, void *p, uintptr size);
bool    runtime_freespecial(Special *s, void *p, uintptr size, bool freed);

enum
{
        TypeInfo_SingleObject = 0,
        TypeInfo_Array = 1,
        TypeInfo_Chan = 2,

        // Enables type information at the end of blocks allocated from heap    
        DebugTypeAtBlockEnd = 0,
};

// Information from the compiler about the layout of stack frames.
typedef struct BitVector BitVector;
struct BitVector
{
        int32 n; // # of bits
        uint32 *data;
};
typedef struct StackMap StackMap;
struct StackMap
{
        int32 n; // number of bitmaps
        int32 nbit; // number of bits in each bitmap
        uint32 data[];
};
enum {
        // Pointer map
        BitsPerPointer = 2,
        BitsDead = 0,
        BitsScalar = 1,
        BitsPointer = 2,
        BitsMultiWord = 3,
        // BitsMultiWord will be set for the first word of a multi-word item.
        // When it is set, one of the following will be set for the second word.
        BitsString = 0,
        BitsSlice = 1,
        BitsIface = 2,
        BitsEface = 3,
};
// Returns pointer map data for the given stackmap index
// (the index is encoded in PCDATA_StackMapIndex).
BitVector       runtime_stackmapdata(StackMap *stackmap, int32 n);

// defined in mgc0.go
void    runtime_gc_m_ptr(Eface*);
void    runtime_gc_g_ptr(Eface*);
void    runtime_gc_itab_ptr(Eface*);

void    runtime_memorydump(void);
int32   runtime_setgcpercent(int32);

// Value we use to mark dead pointers when GODEBUG=gcdead=1.
#define PoisonGC ((uintptr)0xf969696969696969ULL)
#define PoisonStack ((uintptr)0x6868686868686868ULL)

struct Workbuf;
void    runtime_MProf_Mark(struct Workbuf**, void (*)(struct Workbuf**, Obj));
void    runtime_proc_scan(struct Workbuf**, void (*)(struct Workbuf**, Obj));
void    runtime_time_scan(struct Workbuf**, void (*)(struct Workbuf**, Obj));
void    runtime_netpoll_scan(struct Workbuf**, void (*)(struct Workbuf**, Obj));