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
RecordSpan(void * vh,byte * p)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]), &mstats.other_sys);
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]), &mstats.other_sys);
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
runtime_MHeap_Init(MHeap * h)54 runtime_MHeap_Init(MHeap *h)
55 {
56 uint32 i;
57
58 runtime_FixAlloc_Init(&h->spanalloc, sizeof(MSpan), RecordSpan, h, &mstats.mspan_sys);
59 runtime_FixAlloc_Init(&h->cachealloc, sizeof(MCache), nil, nil, &mstats.mcache_sys);
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 void
runtime_MHeap_MapSpans(MHeap * h)69 runtime_MHeap_MapSpans(MHeap *h)
70 {
71 uintptr pagesize;
72 uintptr n;
73
74 // Map spans array, PageSize at a time.
75 n = (uintptr)h->arena_used;
76 n -= (uintptr)h->arena_start;
77 n = n / PageSize * sizeof(h->spans[0]);
78 n = ROUND(n, PageSize);
79 pagesize = getpagesize();
80 n = ROUND(n, pagesize);
81 if(h->spans_mapped >= n)
82 return;
83 runtime_SysMap((byte*)h->spans + h->spans_mapped, n - h->spans_mapped, &mstats.other_sys);
84 h->spans_mapped = n;
85 }
86
87 // Allocate a new span of npage pages from the heap
88 // and record its size class in the HeapMap and HeapMapCache.
89 MSpan*
runtime_MHeap_Alloc(MHeap * h,uintptr npage,int32 sizeclass,int32 acct,int32 zeroed)90 runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, int32 acct, int32 zeroed)
91 {
92 MSpan *s;
93
94 runtime_lock(h);
95 mstats.heap_alloc += runtime_m()->mcache->local_cachealloc;
96 runtime_m()->mcache->local_cachealloc = 0;
97 s = MHeap_AllocLocked(h, npage, sizeclass);
98 if(s != nil) {
99 mstats.heap_inuse += npage<<PageShift;
100 if(acct) {
101 mstats.heap_objects++;
102 mstats.heap_alloc += npage<<PageShift;
103 }
104 }
105 runtime_unlock(h);
106 if(s != nil && *(uintptr*)(s->start<<PageShift) != 0 && zeroed)
107 runtime_memclr((byte*)(s->start<<PageShift), s->npages<<PageShift);
108 return s;
109 }
110
111 static MSpan*
MHeap_AllocLocked(MHeap * h,uintptr npage,int32 sizeclass)112 MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
113 {
114 uintptr n;
115 MSpan *s, *t;
116 PageID p;
117
118 // Try in fixed-size lists up to max.
119 for(n=npage; n < nelem(h->free); n++) {
120 if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
121 s = h->free[n].next;
122 goto HaveSpan;
123 }
124 }
125
126 // Best fit in list of large spans.
127 if((s = MHeap_AllocLarge(h, npage)) == nil) {
128 if(!MHeap_Grow(h, npage))
129 return nil;
130 if((s = MHeap_AllocLarge(h, npage)) == nil)
131 return nil;
132 }
133
134 HaveSpan:
135 // Mark span in use.
136 if(s->state != MSpanFree)
137 runtime_throw("MHeap_AllocLocked - MSpan not free");
138 if(s->npages < npage)
139 runtime_throw("MHeap_AllocLocked - bad npages");
140 runtime_MSpanList_Remove(s);
141 s->state = MSpanInUse;
142 mstats.heap_idle -= s->npages<<PageShift;
143 mstats.heap_released -= s->npreleased<<PageShift;
144 if(s->npreleased > 0) {
145 // We have called runtime_SysUnused with these pages, and on
146 // Unix systems it called madvise. At this point at least
147 // some BSD-based kernels will return these pages either as
148 // zeros or with the old data. For our caller, the first word
149 // in the page indicates whether the span contains zeros or
150 // not (this word was set when the span was freed by
151 // MCentral_Free or runtime_MCentral_FreeSpan). If the first
152 // page in the span is returned as zeros, and some subsequent
153 // page is returned with the old data, then we will be
154 // returning a span that is assumed to be all zeros, but the
155 // actual data will not be all zeros. Avoid that problem by
156 // explicitly marking the span as not being zeroed, just in
157 // case. The beadbead constant we use here means nothing, it
158 // is just a unique constant not seen elsewhere in the
159 // runtime, as a clue in case it turns up unexpectedly in
160 // memory or in a stack trace.
161 runtime_SysUsed((void*)(s->start<<PageShift), s->npages<<PageShift);
162 *(uintptr*)(s->start<<PageShift) = (uintptr)0xbeadbeadbeadbeadULL;
163 }
164 s->npreleased = 0;
165
166 if(s->npages > npage) {
167 // Trim extra and put it back in the heap.
168 t = runtime_FixAlloc_Alloc(&h->spanalloc);
169 runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
170 s->npages = npage;
171 p = t->start;
172 p -= ((uintptr)h->arena_start>>PageShift);
173 if(p > 0)
174 h->spans[p-1] = s;
175 h->spans[p] = t;
176 h->spans[p+t->npages-1] = t;
177 *(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift); // copy "needs zeroing" mark
178 t->state = MSpanInUse;
179 MHeap_FreeLocked(h, t);
180 t->unusedsince = s->unusedsince; // preserve age
181 }
182 s->unusedsince = 0;
183
184 // Record span info, because gc needs to be
185 // able to map interior pointer to containing span.
186 s->sizeclass = sizeclass;
187 s->elemsize = (sizeclass==0 ? s->npages<<PageShift : (uintptr)runtime_class_to_size[sizeclass]);
188 s->types.compression = MTypes_Empty;
189 p = s->start;
190 p -= ((uintptr)h->arena_start>>PageShift);
191 for(n=0; n<npage; n++)
192 h->spans[p+n] = s;
193 return s;
194 }
195
196 // Allocate a span of exactly npage pages from the list of large spans.
197 static MSpan*
MHeap_AllocLarge(MHeap * h,uintptr npage)198 MHeap_AllocLarge(MHeap *h, uintptr npage)
199 {
200 return BestFit(&h->large, npage, nil);
201 }
202
203 // Search list for smallest span with >= npage pages.
204 // If there are multiple smallest spans, take the one
205 // with the earliest starting address.
206 static MSpan*
BestFit(MSpan * list,uintptr npage,MSpan * best)207 BestFit(MSpan *list, uintptr npage, MSpan *best)
208 {
209 MSpan *s;
210
211 for(s=list->next; s != list; s=s->next) {
212 if(s->npages < npage)
213 continue;
214 if(best == nil
215 || s->npages < best->npages
216 || (s->npages == best->npages && s->start < best->start))
217 best = s;
218 }
219 return best;
220 }
221
222 // Try to add at least npage pages of memory to the heap,
223 // returning whether it worked.
224 static bool
MHeap_Grow(MHeap * h,uintptr npage)225 MHeap_Grow(MHeap *h, uintptr npage)
226 {
227 uintptr ask;
228 void *v;
229 MSpan *s;
230 PageID p;
231
232 // Ask for a big chunk, to reduce the number of mappings
233 // the operating system needs to track; also amortizes
234 // the overhead of an operating system mapping.
235 // Allocate a multiple of 64kB (16 pages).
236 npage = (npage+15)&~15;
237 ask = npage<<PageShift;
238 if(ask < HeapAllocChunk)
239 ask = HeapAllocChunk;
240
241 v = runtime_MHeap_SysAlloc(h, ask);
242 if(v == nil) {
243 if(ask > (npage<<PageShift)) {
244 ask = npage<<PageShift;
245 v = runtime_MHeap_SysAlloc(h, ask);
246 }
247 if(v == nil) {
248 runtime_printf("runtime: out of memory: cannot allocate %D-byte block (%D in use)\n", (uint64)ask, mstats.heap_sys);
249 return false;
250 }
251 }
252
253 // Create a fake "in use" span and free it, so that the
254 // right coalescing happens.
255 s = runtime_FixAlloc_Alloc(&h->spanalloc);
256 runtime_MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
257 p = s->start;
258 p -= ((uintptr)h->arena_start>>PageShift);
259 h->spans[p] = s;
260 h->spans[p + s->npages - 1] = s;
261 s->state = MSpanInUse;
262 MHeap_FreeLocked(h, s);
263 return true;
264 }
265
266 // Look up the span at the given address.
267 // Address is guaranteed to be in map
268 // and is guaranteed to be start or end of span.
269 MSpan*
runtime_MHeap_Lookup(MHeap * h,void * v)270 runtime_MHeap_Lookup(MHeap *h, void *v)
271 {
272 uintptr p;
273
274 p = (uintptr)v;
275 p -= (uintptr)h->arena_start;
276 return h->spans[p >> PageShift];
277 }
278
279 // Look up the span at the given address.
280 // Address is *not* guaranteed to be in map
281 // and may be anywhere in the span.
282 // Map entries for the middle of a span are only
283 // valid for allocated spans. Free spans may have
284 // other garbage in their middles, so we have to
285 // check for that.
286 MSpan*
runtime_MHeap_LookupMaybe(MHeap * h,void * v)287 runtime_MHeap_LookupMaybe(MHeap *h, void *v)
288 {
289 MSpan *s;
290 PageID p, q;
291
292 if((byte*)v < h->arena_start || (byte*)v >= h->arena_used)
293 return nil;
294 p = (uintptr)v>>PageShift;
295 q = p;
296 q -= (uintptr)h->arena_start >> PageShift;
297 s = h->spans[q];
298 if(s == nil || p < s->start || (byte*)v >= s->limit || s->state != MSpanInUse)
299 return nil;
300 return s;
301 }
302
303 // Free the span back into the heap.
304 void
runtime_MHeap_Free(MHeap * h,MSpan * s,int32 acct)305 runtime_MHeap_Free(MHeap *h, MSpan *s, int32 acct)
306 {
307 runtime_lock(h);
308 mstats.heap_alloc += runtime_m()->mcache->local_cachealloc;
309 runtime_m()->mcache->local_cachealloc = 0;
310 mstats.heap_inuse -= s->npages<<PageShift;
311 if(acct) {
312 mstats.heap_alloc -= s->npages<<PageShift;
313 mstats.heap_objects--;
314 }
315 MHeap_FreeLocked(h, s);
316 runtime_unlock(h);
317 }
318
319 static void
MHeap_FreeLocked(MHeap * h,MSpan * s)320 MHeap_FreeLocked(MHeap *h, MSpan *s)
321 {
322 uintptr *sp, *tp;
323 MSpan *t;
324 PageID p;
325
326 s->types.compression = MTypes_Empty;
327
328 if(s->state != MSpanInUse || s->ref != 0) {
329 runtime_printf("MHeap_FreeLocked - span %p ptr %p state %d ref %d\n", s, s->start<<PageShift, s->state, s->ref);
330 runtime_throw("MHeap_FreeLocked - invalid free");
331 }
332 mstats.heap_idle += s->npages<<PageShift;
333 s->state = MSpanFree;
334 runtime_MSpanList_Remove(s);
335 sp = (uintptr*)(s->start<<PageShift);
336 // Stamp newly unused spans. The scavenger will use that
337 // info to potentially give back some pages to the OS.
338 s->unusedsince = runtime_nanotime();
339 s->npreleased = 0;
340
341 // Coalesce with earlier, later spans.
342 p = s->start;
343 p -= (uintptr)h->arena_start >> PageShift;
344 if(p > 0 && (t = h->spans[p-1]) != nil && t->state != MSpanInUse) {
345 if(t->npreleased == 0) { // cant't touch this otherwise
346 tp = (uintptr*)(t->start<<PageShift);
347 *tp |= *sp; // propagate "needs zeroing" mark
348 }
349 s->start = t->start;
350 s->npages += t->npages;
351 s->npreleased = t->npreleased; // absorb released pages
352 p -= t->npages;
353 h->spans[p] = s;
354 runtime_MSpanList_Remove(t);
355 t->state = MSpanDead;
356 runtime_FixAlloc_Free(&h->spanalloc, t);
357 }
358 if((p+s->npages)*sizeof(h->spans[0]) < h->spans_mapped && (t = h->spans[p+s->npages]) != nil && t->state != MSpanInUse) {
359 if(t->npreleased == 0) { // cant't touch this otherwise
360 tp = (uintptr*)(t->start<<PageShift);
361 *sp |= *tp; // propagate "needs zeroing" mark
362 }
363 s->npages += t->npages;
364 s->npreleased += t->npreleased;
365 h->spans[p + s->npages - 1] = s;
366 runtime_MSpanList_Remove(t);
367 t->state = MSpanDead;
368 runtime_FixAlloc_Free(&h->spanalloc, t);
369 }
370
371 // Insert s into appropriate list.
372 if(s->npages < nelem(h->free))
373 runtime_MSpanList_Insert(&h->free[s->npages], s);
374 else
375 runtime_MSpanList_Insert(&h->large, s);
376 }
377
378 static void
forcegchelper(void * vnote)379 forcegchelper(void *vnote)
380 {
381 Note *note = (Note*)vnote;
382
383 runtime_gc(1);
384 runtime_notewakeup(note);
385 }
386
387 static uintptr
scavengelist(MSpan * list,uint64 now,uint64 limit)388 scavengelist(MSpan *list, uint64 now, uint64 limit)
389 {
390 uintptr released, sumreleased, start, end, pagesize;
391 MSpan *s;
392
393 if(runtime_MSpanList_IsEmpty(list))
394 return 0;
395
396 sumreleased = 0;
397 for(s=list->next; s != list; s=s->next) {
398 if((now - s->unusedsince) > limit && s->npreleased != s->npages) {
399 released = (s->npages - s->npreleased) << PageShift;
400 mstats.heap_released += released;
401 sumreleased += released;
402 s->npreleased = s->npages;
403
404 start = s->start << PageShift;
405 end = start + (s->npages << PageShift);
406
407 // Round start up and end down to ensure we
408 // are acting on entire pages.
409 pagesize = getpagesize();
410 start = ROUND(start, pagesize);
411 end &= ~(pagesize - 1);
412 if(end > start)
413 runtime_SysUnused((void*)start, end - start);
414 }
415 }
416 return sumreleased;
417 }
418
419 static void
scavenge(int32 k,uint64 now,uint64 limit)420 scavenge(int32 k, uint64 now, uint64 limit)
421 {
422 uint32 i;
423 uintptr sumreleased;
424 MHeap *h;
425
426 h = &runtime_mheap;
427 sumreleased = 0;
428 for(i=0; i < nelem(h->free); i++)
429 sumreleased += scavengelist(&h->free[i], now, limit);
430 sumreleased += scavengelist(&h->large, now, limit);
431
432 if(runtime_debug.gctrace > 0) {
433 if(sumreleased > 0)
434 runtime_printf("scvg%d: %D MB released\n", k, (uint64)sumreleased>>20);
435 runtime_printf("scvg%d: inuse: %D, idle: %D, sys: %D, released: %D, consumed: %D (MB)\n",
436 k, mstats.heap_inuse>>20, mstats.heap_idle>>20, mstats.heap_sys>>20,
437 mstats.heap_released>>20, (mstats.heap_sys - mstats.heap_released)>>20);
438 }
439 }
440
441 // Release (part of) unused memory to OS.
442 // Goroutine created at startup.
443 // Loop forever.
444 void
runtime_MHeap_Scavenger(void * dummy)445 runtime_MHeap_Scavenger(void* dummy)
446 {
447 G *g;
448 MHeap *h;
449 uint64 tick, now, forcegc, limit;
450 uint32 k;
451 Note note, *notep;
452
453 USED(dummy);
454
455 g = runtime_g();
456 g->issystem = true;
457 g->isbackground = true;
458
459 // If we go two minutes without a garbage collection, force one to run.
460 forcegc = 2*60*1e9;
461 // If a span goes unused for 5 minutes after a garbage collection,
462 // we hand it back to the operating system.
463 limit = 5*60*1e9;
464 // Make wake-up period small enough for the sampling to be correct.
465 if(forcegc < limit)
466 tick = forcegc/2;
467 else
468 tick = limit/2;
469
470 h = &runtime_mheap;
471 for(k=0;; k++) {
472 runtime_noteclear(¬e);
473 runtime_notetsleepg(¬e, tick);
474
475 runtime_lock(h);
476 now = runtime_nanotime();
477 if(now - mstats.last_gc > forcegc) {
478 runtime_unlock(h);
479 // The scavenger can not block other goroutines,
480 // otherwise deadlock detector can fire spuriously.
481 // GC blocks other goroutines via the runtime_worldsema.
482 runtime_noteclear(¬e);
483 notep = ¬e;
484 __go_go(forcegchelper, (void*)notep);
485 runtime_notetsleepg(¬e, -1);
486 if(runtime_debug.gctrace > 0)
487 runtime_printf("scvg%d: GC forced\n", k);
488 runtime_lock(h);
489 now = runtime_nanotime();
490 }
491 scavenge(k, now, limit);
492 runtime_unlock(h);
493 }
494 }
495
496 void runtime_debug_freeOSMemory(void) __asm__("runtime_debug.freeOSMemory");
497
498 void
runtime_debug_freeOSMemory(void)499 runtime_debug_freeOSMemory(void)
500 {
501 runtime_gc(1);
502 runtime_lock(&runtime_mheap);
503 scavenge(-1, ~(uintptr)0, 0);
504 runtime_unlock(&runtime_mheap);
505 }
506
507 // Initialize a new span with the given start and npages.
508 void
runtime_MSpan_Init(MSpan * span,PageID start,uintptr npages)509 runtime_MSpan_Init(MSpan *span, PageID start, uintptr npages)
510 {
511 span->next = nil;
512 span->prev = nil;
513 span->start = start;
514 span->npages = npages;
515 span->freelist = nil;
516 span->ref = 0;
517 span->sizeclass = 0;
518 span->elemsize = 0;
519 span->state = 0;
520 span->unusedsince = 0;
521 span->npreleased = 0;
522 span->types.compression = MTypes_Empty;
523 }
524
525 // Initialize an empty doubly-linked list.
526 void
runtime_MSpanList_Init(MSpan * list)527 runtime_MSpanList_Init(MSpan *list)
528 {
529 list->state = MSpanListHead;
530 list->next = list;
531 list->prev = list;
532 }
533
534 void
runtime_MSpanList_Remove(MSpan * span)535 runtime_MSpanList_Remove(MSpan *span)
536 {
537 if(span->prev == nil && span->next == nil)
538 return;
539 span->prev->next = span->next;
540 span->next->prev = span->prev;
541 span->prev = nil;
542 span->next = nil;
543 }
544
545 bool
runtime_MSpanList_IsEmpty(MSpan * list)546 runtime_MSpanList_IsEmpty(MSpan *list)
547 {
548 return list->next == list;
549 }
550
551 void
runtime_MSpanList_Insert(MSpan * list,MSpan * span)552 runtime_MSpanList_Insert(MSpan *list, MSpan *span)
553 {
554 if(span->next != nil || span->prev != nil) {
555 runtime_printf("failed MSpanList_Insert %p %p %p\n", span, span->next, span->prev);
556 runtime_throw("MSpanList_Insert");
557 }
558 span->next = list->next;
559 span->prev = list;
560 span->next->prev = span;
561 span->prev->next = span;
562 }
563
564
565