libgo/runtime/mheap.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 // Page heap.
   6 //
   7 // See malloc.h for overview.
   8 //
   9 // When a MSpan is in the heap free list, state == MSpanFree
  10 // and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
  11 //
  12 // When a MSpan is allocated, state == MSpanInUse
  13 // and heapmap(i) == span for all s->start <= i < s->start+s->npages.
  14
  15 #include "runtime.h"
  16 #include "arch.h"
  17 #include "malloc.h"
  18
  19 static MSpan *MHeap_AllocLocked(MHeap*, uintptr, int32);
  20 static bool MHeap_Grow(MHeap*, uintptr);
  21 static void MHeap_FreeLocked(MHeap*, MSpan*);
  22 static MSpan *MHeap_AllocLarge(MHeap*, uintptr);
  23 static MSpan *BestFit(MSpan*, uintptr, MSpan*);
  24
  25 static void
  26 RecordSpan(void *vh, byte *p)
  27 {
  28         MHeap *h;
  29         MSpan *s;
  30         MSpan **all;
  31         uint32 cap;
  32
  33         h = vh;
  34         s = (MSpan*)p;
  35         if(h->nspan >= h->nspancap) {
  36                 cap = 64*1024/sizeof(all[0]);
  37                 if(cap < h->nspancap*3/2)
  38                         cap = h->nspancap*3/2;
  39                 all = (MSpan**)runtime_SysAlloc(cap*sizeof(all[0]));
  40                 if(all == nil)
  41                         runtime_throw("runtime: cannot allocate memory");
  42                 if(h->allspans) {
  43                         runtime_memmove(all, h->allspans, h->nspancap*sizeof(all[0]));
  44                         runtime_SysFree(h->allspans, h->nspancap*sizeof(all[0]));
  45                 }
  46                 h->allspans = all;
  47                 h->nspancap = cap;
  48         }
  49         h->allspans[h->nspan++] = s;
  50 }
  51
  52 // Initialize the heap; fetch memory using alloc.
  53 void
  54 runtime_MHeap_Init(MHeap *h, void *(*alloc)(uintptr))
  55 {
  56         uint32 i;
  57
  58         runtime_FixAlloc_Init(&h->spanalloc, sizeof(MSpan), alloc, RecordSpan, h);
  59         runtime_FixAlloc_Init(&h->cachealloc, sizeof(MCache), alloc, nil, nil);
  60         // h->mapcache needs no init
  61         for(i=0; i<nelem(h->free); i++)
  62                 runtime_MSpanList_Init(&h->free[i]);
  63         runtime_MSpanList_Init(&h->large);
  64         for(i=0; i<nelem(h->central); i++)
  65                 runtime_MCentral_Init(&h->central[i], i);
  66 }
  67
  68 // Allocate a new span of npage pages from the heap
  69 // and record its size class in the HeapMap and HeapMapCache.
  70 MSpan*
  71 runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, int32 acct, int32 zeroed)
  72 {
  73         MSpan *s;
  74
  75         runtime_lock(h);
  76         runtime_purgecachedstats(runtime_m()->mcache);
  77         s = MHeap_AllocLocked(h, npage, sizeclass);
  78         if(s != nil) {
  79                 mstats.heap_inuse += npage<<PageShift;
  80                 if(acct) {
  81                         mstats.heap_objects++;
  82                         mstats.heap_alloc += npage<<PageShift;
  83                 }
  84         }
  85         runtime_unlock(h);
  86         if(s != nil && *(uintptr*)(s->start<<PageShift) != 0 && zeroed)
  87                 runtime_memclr((byte*)(s->start<<PageShift), s->npages<<PageShift);
  88         return s;
  89 }
  90
  91 static MSpan*
  92 MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
  93 {
  94         uintptr n;
  95         MSpan *s, *t;
  96         PageID p;
  97
  98         // Try in fixed-size lists up to max.
  99         for(n=npage; n < nelem(h->free); n++) {
 100                 if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
 101                         s = h->free[n].next;
 102                         goto HaveSpan;
 103                 }
 104         }
 105
 106         // Best fit in list of large spans.
 107         if((s = MHeap_AllocLarge(h, npage)) == nil) {
 108                 if(!MHeap_Grow(h, npage))
 109                         return nil;
 110                 if((s = MHeap_AllocLarge(h, npage)) == nil)
 111                         return nil;
 112         }
 113
 114 HaveSpan:
 115         // Mark span in use.
 116         if(s->state != MSpanFree)
 117                 runtime_throw("MHeap_AllocLocked - MSpan not free");
 118         if(s->npages < npage)
 119                 runtime_throw("MHeap_AllocLocked - bad npages");
 120         runtime_MSpanList_Remove(s);
 121         s->state = MSpanInUse;
 122         mstats.heap_idle -= s->npages<<PageShift;
 123         mstats.heap_released -= s->npreleased<<PageShift;
 124         if(s->npreleased > 0) {
 125                 // We have called runtime_SysUnused with these pages, and on
 126                 // Unix systems it called madvise.  At this point at least
 127                 // some BSD-based kernels will return these pages either as
 128                 // zeros or with the old data.  For our caller, the first word
 129                 // in the page indicates whether the span contains zeros or
 130                 // not (this word was set when the span was freed by
 131                 // MCentral_Free or runtime_MCentral_FreeSpan).  If the first
 132                 // page in the span is returned as zeros, and some subsequent
 133                 // page is returned with the old data, then we will be
 134                 // returning a span that is assumed to be all zeros, but the
 135                 // actual data will not be all zeros.  Avoid that problem by
 136                 // explicitly marking the span as not being zeroed, just in
 137                 // case.  The beadbead constant we use here means nothing, it
 138                 // is just a unique constant not seen elsewhere in the
 139                 // runtime, as a clue in case it turns up unexpectedly in
 140                 // memory or in a stack trace.
 141                 *(uintptr*)(s->start<<PageShift) = (uintptr)0xbeadbeadbeadbeadULL;
 142         }
 143         s->npreleased = 0;
 144
 145         if(s->npages > npage) {
 146                 // Trim extra and put it back in the heap.
 147                 t = runtime_FixAlloc_Alloc(&h->spanalloc);
 148                 mstats.mspan_inuse = h->spanalloc.inuse;
 149                 mstats.mspan_sys = h->spanalloc.sys;
 150                 runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
 151                 s->npages = npage;
 152                 p = t->start;
 153                 if(sizeof(void*) == 8)
 154                         p -= ((uintptr)h->arena_start>>PageShift);
 155                 if(p > 0)
 156                         h->map[p-1] = s;
 157                 h->map[p] = t;
 158                 h->map[p+t->npages-1] = t;
 159                 *(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift);  // copy "needs zeroing" mark
 160                 t->state = MSpanInUse;
 161                 MHeap_FreeLocked(h, t);
 162                 t->unusedsince = s->unusedsince; // preserve age
 163         }
 164         s->unusedsince = 0;
 165
 166         // Record span info, because gc needs to be
 167         // able to map interior pointer to containing span.
 168         s->sizeclass = sizeclass;
 169         s->elemsize = (sizeclass==0 ? s->npages<<PageShift : (uintptr)runtime_class_to_size[sizeclass]);
 170         s->types.compression = MTypes_Empty;
 171         p = s->start;
 172         if(sizeof(void*) == 8)
 173                 p -= ((uintptr)h->arena_start>>PageShift);
 174         for(n=0; n<npage; n++)
 175                 h->map[p+n] = s;
 176         return s;
 177 }
 178
 179 // Allocate a span of exactly npage pages from the list of large spans.
 180 static MSpan*
 181 MHeap_AllocLarge(MHeap *h, uintptr npage)
 182 {
 183         return BestFit(&h->large, npage, nil);
 184 }
 185
 186 // Search list for smallest span with >= npage pages.
 187 // If there are multiple smallest spans, take the one
 188 // with the earliest starting address.
 189 static MSpan*
 190 BestFit(MSpan *list, uintptr npage, MSpan *best)
 191 {
 192         MSpan *s;
 193
 194         for(s=list->next; s != list; s=s->next) {
 195                 if(s->npages < npage)
 196                         continue;
 197                 if(best == nil
 198                 || s->npages < best->npages
 199                 || (s->npages == best->npages && s->start < best->start))
 200                         best = s;
 201         }
 202         return best;
 203 }
 204
 205 // Try to add at least npage pages of memory to the heap,
 206 // returning whether it worked.
 207 static bool
 208 MHeap_Grow(MHeap *h, uintptr npage)
 209 {
 210         uintptr ask;
 211         void *v;
 212         MSpan *s;
 213         PageID p;
 214
 215         // Ask for a big chunk, to reduce the number of mappings
 216         // the operating system needs to track; also amortizes
 217         // the overhead of an operating system mapping.
 218         // Allocate a multiple of 64kB (16 pages).
 219         npage = (npage+15)&~15;
 220         ask = npage<<PageShift;
 221         if(ask < HeapAllocChunk)
 222                 ask = HeapAllocChunk;
 223
 224         v = runtime_MHeap_SysAlloc(h, ask);
 225         if(v == nil) {
 226                 if(ask > (npage<<PageShift)) {
 227                         ask = npage<<PageShift;
 228                         v = runtime_MHeap_SysAlloc(h, ask);
 229                 }
 230                 if(v == nil) {
 231                         runtime_printf("runtime: out of memory: cannot allocate %D-byte block (%D in use)\n", (uint64)ask, mstats.heap_sys);
 232                         return false;
 233                 }
 234         }
 235         mstats.heap_sys += ask;
 236
 237         // Create a fake "in use" span and free it, so that the
 238         // right coalescing happens.
 239         s = runtime_FixAlloc_Alloc(&h->spanalloc);
 240         mstats.mspan_inuse = h->spanalloc.inuse;
 241         mstats.mspan_sys = h->spanalloc.sys;
 242         runtime_MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
 243         p = s->start;
 244         if(sizeof(void*) == 8)
 245                 p -= ((uintptr)h->arena_start>>PageShift);
 246         h->map[p] = s;
 247         h->map[p + s->npages - 1] = s;
 248         s->state = MSpanInUse;
 249         MHeap_FreeLocked(h, s);
 250         return true;
 251 }
 252
 253 // Look up the span at the given address.
 254 // Address is guaranteed to be in map
 255 // and is guaranteed to be start or end of span.
 256 MSpan*
 257 runtime_MHeap_Lookup(MHeap *h, void *v)
 258 {
 259         uintptr p;
 260
 261         p = (uintptr)v;
 262         if(sizeof(void*) == 8)
 263                 p -= (uintptr)h->arena_start;
 264         return h->map[p >> PageShift];
 265 }
 266
 267 // Look up the span at the given address.
 268 // Address is *not* guaranteed to be in map
 269 // and may be anywhere in the span.
 270 // Map entries for the middle of a span are only
 271 // valid for allocated spans.  Free spans may have
 272 // other garbage in their middles, so we have to
 273 // check for that.
 274 MSpan*
 275 runtime_MHeap_LookupMaybe(MHeap *h, void *v)
 276 {
 277         MSpan *s;
 278         PageID p, q;
 279
 280         if((byte*)v < h->arena_start || (byte*)v >= h->arena_used)
 281                 return nil;
 282         p = (uintptr)v>>PageShift;
 283         q = p;
 284         if(sizeof(void*) == 8)
 285                 q -= (uintptr)h->arena_start >> PageShift;
 286         s = h->map[q];
 287         if(s == nil || p < s->start || p - s->start >= s->npages)
 288                 return nil;
 289         if(s->state != MSpanInUse)
 290                 return nil;
 291         return s;
 292 }
 293
 294 // Free the span back into the heap.
 295 void
 296 runtime_MHeap_Free(MHeap *h, MSpan *s, int32 acct)
 297 {
 298         runtime_lock(h);
 299         runtime_purgecachedstats(runtime_m()->mcache);
 300         mstats.heap_inuse -= s->npages<<PageShift;
 301         if(acct) {
 302                 mstats.heap_alloc -= s->npages<<PageShift;
 303                 mstats.heap_objects--;
 304         }
 305         MHeap_FreeLocked(h, s);
 306         runtime_unlock(h);
 307 }
 308
 309 static void
 310 MHeap_FreeLocked(MHeap *h, MSpan *s)
 311 {
 312         uintptr *sp, *tp;
 313         MSpan *t;
 314         PageID p;
 315
 316         if(s->types.sysalloc)
 317                 runtime_settype_sysfree(s);
 318         s->types.compression = MTypes_Empty;
 319
 320         if(s->state != MSpanInUse || s->ref != 0) {
 321                 runtime_printf("MHeap_FreeLocked - span %p ptr %p state %d ref %d\n", s, s->start<<PageShift, s->state, s->ref);
 322                 runtime_throw("MHeap_FreeLocked - invalid free");
 323         }
 324         mstats.heap_idle += s->npages<<PageShift;
 325         s->state = MSpanFree;
 326         runtime_MSpanList_Remove(s);
 327         sp = (uintptr*)(s->start<<PageShift);
 328         // Stamp newly unused spans. The scavenger will use that
 329         // info to potentially give back some pages to the OS.
 330         s->unusedsince = runtime_nanotime();
 331         s->npreleased = 0;
 332
 333         // Coalesce with earlier, later spans.
 334         p = s->start;
 335         if(sizeof(void*) == 8)
 336                 p -= (uintptr)h->arena_start >> PageShift;
 337         if(p > 0 && (t = h->map[p-1]) != nil && t->state != MSpanInUse) {
 338                 tp = (uintptr*)(t->start<<PageShift);
 339                 *tp |= *sp;     // propagate "needs zeroing" mark
 340                 s->start = t->start;
 341                 s->npages += t->npages;
 342                 s->npreleased = t->npreleased; // absorb released pages
 343                 p -= t->npages;
 344                 h->map[p] = s;
 345                 runtime_MSpanList_Remove(t);
 346                 t->state = MSpanDead;
 347                 runtime_FixAlloc_Free(&h->spanalloc, t);
 348                 mstats.mspan_inuse = h->spanalloc.inuse;
 349                 mstats.mspan_sys = h->spanalloc.sys;
 350         }
 351         if(p+s->npages < nelem(h->map) && (t = h->map[p+s->npages]) != nil && t->state != MSpanInUse) {
 352                 tp = (uintptr*)(t->start<<PageShift);
 353                 *sp |= *tp;     // propagate "needs zeroing" mark
 354                 s->npages += t->npages;
 355                 s->npreleased += t->npreleased;
 356                 h->map[p + s->npages - 1] = s;
 357                 runtime_MSpanList_Remove(t);
 358                 t->state = MSpanDead;
 359                 runtime_FixAlloc_Free(&h->spanalloc, t);
 360                 mstats.mspan_inuse = h->spanalloc.inuse;
 361                 mstats.mspan_sys = h->spanalloc.sys;
 362         }
 363
 364         // Insert s into appropriate list.
 365         if(s->npages < nelem(h->free))
 366                 runtime_MSpanList_Insert(&h->free[s->npages], s);
 367         else
 368                 runtime_MSpanList_Insert(&h->large, s);
 369 }
 370
 371 static void
 372 forcegchelper(void *vnote)
 373 {
 374         Note *note = (Note*)vnote;
 375
 376         runtime_gc(1);
 377         runtime_notewakeup(note);
 378 }
 379
 380 static uintptr
 381 scavengelist(MSpan *list, uint64 now, uint64 limit)
 382 {
 383         uintptr released, sumreleased;
 384         MSpan *s;
 385
 386         if(runtime_MSpanList_IsEmpty(list))
 387                 return 0;
 388
 389         sumreleased = 0;
 390         for(s=list->next; s != list; s=s->next) {
 391                 if((now - s->unusedsince) > limit) {
 392                         released = (s->npages - s->npreleased) << PageShift;
 393                         mstats.heap_released += released;
 394                         sumreleased += released;
 395                         s->npreleased = s->npages;
 396                         runtime_SysUnused((void*)(s->start << PageShift), s->npages << PageShift);
 397                 }
 398         }
 399         return sumreleased;
 400 }
 401
 402 static uintptr
 403 scavenge(uint64 now, uint64 limit)
 404 {
 405         uint32 i;
 406         uintptr sumreleased;
 407         MHeap *h;
 408
 409         h = runtime_mheap;
 410         sumreleased = 0;
 411         for(i=0; i < nelem(h->free); i++)
 412                 sumreleased += scavengelist(&h->free[i], now, limit);
 413         sumreleased += scavengelist(&h->large, now, limit);
 414         return sumreleased;
 415 }
 416
 417 // Release (part of) unused memory to OS.
 418 // Goroutine created at startup.
 419 // Loop forever.
 420 void
 421 runtime_MHeap_Scavenger(void* dummy)
 422 {
 423         G *g;
 424         MHeap *h;
 425         uint64 tick, now, forcegc, limit;
 426         uint32 k;
 427         uintptr sumreleased;
 428         const byte *env;
 429         bool trace;
 430         Note note, *notep;
 431
 432         USED(dummy);
 433
 434         g = runtime_g();
 435         g->issystem = true;
 436         g->isbackground = true;
 437
 438         // If we go two minutes without a garbage collection, force one to run.
 439         forcegc = 2*60*1e9;
 440         // If a span goes unused for 5 minutes after a garbage collection,
 441         // we hand it back to the operating system.
 442         limit = 5*60*1e9;
 443         // Make wake-up period small enough for the sampling to be correct.
 444         if(forcegc < limit)
 445                 tick = forcegc/2;
 446         else
 447                 tick = limit/2;
 448
 449         trace = false;
 450         env = runtime_getenv("GOGCTRACE");
 451         if(env != nil)
 452                 trace = runtime_atoi(env) > 0;
 453
 454         h = runtime_mheap;
 455         for(k=0;; k++) {
 456                 runtime_noteclear(&note);
 457                 runtime_entersyscallblock();
 458                 runtime_notetsleep(&note, tick);
 459                 runtime_exitsyscall();
 460
 461                 runtime_lock(h);
 462                 now = runtime_nanotime();
 463                 if(now - mstats.last_gc > forcegc) {
 464                         runtime_unlock(h);
 465                         // The scavenger can not block other goroutines,
 466                         // otherwise deadlock detector can fire spuriously.
 467                         // GC blocks other goroutines via the runtime_worldsema.
 468                         runtime_noteclear(&note);
 469                         notep = &note;
 470                         __go_go(forcegchelper, (void*)notep);
 471                         runtime_entersyscallblock();
 472                         runtime_notesleep(&note);
 473                         runtime_exitsyscall();
 474                         if(trace)
 475                                 runtime_printf("scvg%d: GC forced\n", k);
 476                         runtime_lock(h);
 477                         now = runtime_nanotime();
 478                 }
 479                 sumreleased = scavenge(now, limit);
 480                 runtime_unlock(h);
 481
 482                 if(trace) {
 483                         if(sumreleased > 0)
 484                                 runtime_printf("scvg%d: %p MB released\n", k, sumreleased>>20);
 485                         runtime_printf("scvg%d: inuse: %D, idle: %D, sys: %D, released: %D, consumed: %D (MB)\n",
 486                                 k, mstats.heap_inuse>>20, mstats.heap_idle>>20, mstats.heap_sys>>20,
 487                                 mstats.heap_released>>20, (mstats.heap_sys - mstats.heap_released)>>20);
 488                 }
 489         }
 490 }
 491
 492 void runtime_debug_freeOSMemory(void) __asm__("runtime_debug.freeOSMemory");
 493
 494 void
 495 runtime_debug_freeOSMemory(void)
 496 {
 497         runtime_gc(1);
 498         runtime_lock(runtime_mheap);
 499         scavenge(~(uintptr)0, 0);
 500         runtime_unlock(runtime_mheap);
 501 }
 502
 503 // Initialize a new span with the given start and npages.
 504 void
 505 runtime_MSpan_Init(MSpan *span, PageID start, uintptr npages)
 506 {
 507         span->next = nil;
 508         span->prev = nil;
 509         span->start = start;
 510         span->npages = npages;
 511         span->freelist = nil;
 512         span->ref = 0;
 513         span->sizeclass = 0;
 514         span->elemsize = 0;
 515         span->state = 0;
 516         span->unusedsince = 0;
 517         span->npreleased = 0;
 518         span->types.compression = MTypes_Empty;
 519 }
 520
 521 // Initialize an empty doubly-linked list.
 522 void
 523 runtime_MSpanList_Init(MSpan *list)
 524 {
 525         list->state = MSpanListHead;
 526         list->next = list;
 527         list->prev = list;
 528 }
 529
 530 void
 531 runtime_MSpanList_Remove(MSpan *span)
 532 {
 533         if(span->prev == nil && span->next == nil)
 534                 return;
 535         span->prev->next = span->next;
 536         span->next->prev = span->prev;
 537         span->prev = nil;
 538         span->next = nil;
 539 }
 540
 541 bool
 542 runtime_MSpanList_IsEmpty(MSpan *list)
 543 {
 544         return list->next == list;
 545 }
 546
 547 void
 548 runtime_MSpanList_Insert(MSpan *list, MSpan *span)
 549 {
 550         if(span->next != nil || span->prev != nil) {
 551                 runtime_printf("failed MSpanList_Insert %p %p %p\n", span, span->next, span->prev);
 552                 runtime_throw("MSpanList_Insert");
 553         }
 554         span->next = list->next;
 555         span->prev = list;
 556         span->next->prev = span;
 557         span->prev->next = span;
 558 }
 559
 560