libgo/runtime/mcentral.c

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Central free lists.
   6 //
   7 // See malloc.h for an overview.
   8 //
   9 // The MCentral doesn't actually contain the list of free objects; the MSpan does.
  10 // Each MCentral is two lists of MSpans: those with free objects (c->nonempty)
  11 // and those that are completely allocated (c->empty).
  12 //
  13 // TODO(rsc): tcmalloc uses a "transfer cache" to split the list
  14 // into sections of class_to_transfercount[sizeclass] objects
  15 // so that it is faster to move those lists between MCaches and MCentrals.
  16
  17 #include "runtime.h"
  18 #include "arch.h"
  19 #include "malloc.h"
  20
  21 static bool MCentral_Grow(MCentral *c);
  22 static void* MCentral_Alloc(MCentral *c);
  23 static void MCentral_Free(MCentral *c, void *v);
  24
  25 // Initialize a single central free list.
  26 void
  27 runtime_MCentral_Init(MCentral *c, int32 sizeclass)
  28 {
  29         c->sizeclass = sizeclass;
  30         runtime_MSpanList_Init(&c->nonempty);
  31         runtime_MSpanList_Init(&c->empty);
  32 }
  33
  34 // Allocate up to n objects from the central free list.
  35 // Return the number of objects allocated.
  36 // The objects are linked together by their first words.
  37 // On return, *pstart points at the first object and *pend at the last.
  38 int32
  39 runtime_MCentral_AllocList(MCentral *c, int32 n, MLink **pfirst)
  40 {
  41         MLink *first, *last, *v;
  42         int32 i;
  43
  44         runtime_lock(c);
  45         // Replenish central list if empty.
  46         if(runtime_MSpanList_IsEmpty(&c->nonempty)) {
  47                 if(!MCentral_Grow(c)) {
  48                         runtime_unlock(c);
  49                         *pfirst = nil;
  50                         return 0;
  51                 }
  52         }
  53
  54         // Copy from list, up to n.
  55         // First one is guaranteed to work, because we just grew the list.
  56         first = MCentral_Alloc(c);
  57         last = first;
  58         for(i=1; i<n && (v = MCentral_Alloc(c)) != nil; i++) {
  59                 last->next = v;
  60                 last = v;
  61         }
  62         last->next = nil;
  63         c->nfree -= i;
  64
  65         runtime_unlock(c);
  66         *pfirst = first;
  67         return i;
  68 }
  69
  70 // Helper: allocate one object from the central free list.
  71 static void*
  72 MCentral_Alloc(MCentral *c)
  73 {
  74         MSpan *s;
  75         MLink *v;
  76
  77         if(runtime_MSpanList_IsEmpty(&c->nonempty))
  78                 return nil;
  79         s = c->nonempty.next;
  80         s->ref++;
  81         v = s->freelist;
  82         s->freelist = v->next;
  83         if(s->freelist == nil) {
  84                 runtime_MSpanList_Remove(s);
  85                 runtime_MSpanList_Insert(&c->empty, s);
  86         }
  87         return v;
  88 }
  89
  90 // Free n objects back into the central free list.
  91 // Return the number of objects allocated.
  92 // The objects are linked together by their first words.
  93 // On return, *pstart points at the first object and *pend at the last.
  94 void
  95 runtime_MCentral_FreeList(MCentral *c, int32 n, MLink *start)
  96 {
  97         MLink *v, *next;
  98
  99         // Assume next == nil marks end of list.
 100         // n and end would be useful if we implemented
 101         // the transfer cache optimization in the TODO above.
 102         USED(n);
 103
 104         runtime_lock(c);
 105         for(v=start; v; v=next) {
 106                 next = v->next;
 107                 MCentral_Free(c, v);
 108         }
 109         runtime_unlock(c);
 110 }
 111
 112 // Helper: free one object back into the central free list.
 113 static void
 114 MCentral_Free(MCentral *c, void *v)
 115 {
 116         MSpan *s;
 117         MLink *p;
 118         int32 size;
 119
 120         // Find span for v.
 121         s = runtime_MHeap_Lookup(&runtime_mheap, v);
 122         if(s == nil || s->ref == 0)
 123                 runtime_throw("invalid free");
 124
 125         // Move to nonempty if necessary.
 126         if(s->freelist == nil) {
 127                 runtime_MSpanList_Remove(s);
 128                 runtime_MSpanList_Insert(&c->nonempty, s);
 129         }
 130
 131         // Add v back to s's free list.
 132         p = v;
 133         p->next = s->freelist;
 134         s->freelist = p;
 135         c->nfree++;
 136
 137         // If s is completely freed, return it to the heap.
 138         if(--s->ref == 0) {
 139                 size = runtime_class_to_size[c->sizeclass];
 140                 runtime_MSpanList_Remove(s);
 141                 runtime_unmarkspan((byte*)(s->start<<PageShift), s->npages<<PageShift);
 142                 *(uintptr*)(s->start<<PageShift) = 1;  // needs zeroing
 143                 s->freelist = nil;
 144                 c->nfree -= (s->npages << PageShift) / size;
 145                 runtime_unlock(c);
 146                 runtime_MHeap_Free(&runtime_mheap, s, 0);
 147                 runtime_lock(c);
 148         }
 149 }
 150
 151 void
 152 runtime_MGetSizeClassInfo(int32 sizeclass, uintptr *sizep, int32 *npagesp, int32 *nobj)
 153 {
 154         int32 size;
 155         int32 npages;
 156
 157         npages = runtime_class_to_allocnpages[sizeclass];
 158         size = runtime_class_to_size[sizeclass];
 159         *npagesp = npages;
 160         *sizep = size;
 161         *nobj = (npages << PageShift) / size;
 162 }
 163
 164 // Fetch a new span from the heap and
 165 // carve into objects for the free list.
 166 static bool
 167 MCentral_Grow(MCentral *c)
 168 {
 169         int32 i, n, npages;
 170         uintptr size;
 171         MLink **tailp, *v;
 172         byte *p;
 173         MSpan *s;
 174
 175         runtime_unlock(c);
 176         runtime_MGetSizeClassInfo(c->sizeclass, &size, &npages, &n);
 177         s = runtime_MHeap_Alloc(&runtime_mheap, npages, c->sizeclass, 0);
 178         if(s == nil) {
 179                 // TODO(rsc): Log out of memory
 180                 runtime_lock(c);
 181                 return false;
 182         }
 183
 184         // Carve span into sequence of blocks.
 185         tailp = &s->freelist;
 186         p = (byte*)(s->start << PageShift);
 187         s->limit = p + size*n;
 188         for(i=0; i<n; i++) {
 189                 v = (MLink*)p;
 190                 *tailp = v;
 191                 tailp = &v->next;
 192                 p += size;
 193         }
 194         *tailp = nil;
 195         runtime_markspan((byte*)(s->start<<PageShift), size, n, size*n < (s->npages<<PageShift));
 196
 197         runtime_lock(c);
 198         c->nfree += n;
 199         runtime_MSpanList_Insert(&c->nonempty, s);
 200         return true;
 201 }