Merge remote branch 'origin/master' into ghc-new-co
[ghc.git] / rts / sm / GC.c
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 1998-2008
4 *
5 * Generational garbage collector
6 *
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
9 *
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
11 *
12 * ---------------------------------------------------------------------------*/
13
14 #include "PosixSource.h"
15 #include "Rts.h"
16 #include "HsFFI.h"
17
18 #include "Storage.h"
19 #include "RtsUtils.h"
20 #include "Apply.h"
21 #include "Updates.h"
22 #include "Stats.h"
23 #include "Schedule.h"
24 #include "Sanity.h"
25 #include "BlockAlloc.h"
26 #include "ProfHeap.h"
27 #include "Weak.h"
28 #include "Prelude.h"
29 #include "RtsSignals.h"
30 #include "STM.h"
31 #if defined(RTS_GTK_FRONTPANEL)
32 #include "FrontPanel.h"
33 #endif
34 #include "Trace.h"
35 #include "RetainerProfile.h"
36 #include "LdvProfile.h"
37 #include "RaiseAsync.h"
38 #include "Papi.h"
39 #include "Stable.h"
40
41 #include "GC.h"
42 #include "GCThread.h"
43 #include "GCTDecl.h"
44 #include "Compact.h"
45 #include "Evac.h"
46 #include "Scav.h"
47 #include "GCUtils.h"
48 #include "MarkStack.h"
49 #include "MarkWeak.h"
50 #include "Sparks.h"
51 #include "Sweep.h"
52
53 #include <string.h> // for memset()
54 #include <unistd.h>
55
56 /* -----------------------------------------------------------------------------
57 Global variables
58 -------------------------------------------------------------------------- */
59
60 /* STATIC OBJECT LIST.
61 *
62 * During GC:
63 * We maintain a linked list of static objects that are still live.
64 * The requirements for this list are:
65 *
66 * - we need to scan the list while adding to it, in order to
67 * scavenge all the static objects (in the same way that
68 * breadth-first scavenging works for dynamic objects).
69 *
70 * - we need to be able to tell whether an object is already on
71 * the list, to break loops.
72 *
73 * Each static object has a "static link field", which we use for
74 * linking objects on to the list. We use a stack-type list, consing
75 * objects on the front as they are added (this means that the
76 * scavenge phase is depth-first, not breadth-first, but that
77 * shouldn't matter).
78 *
79 * A separate list is kept for objects that have been scavenged
80 * already - this is so that we can zero all the marks afterwards.
81 *
82 * An object is on the list if its static link field is non-zero; this
83 * means that we have to mark the end of the list with '1', not NULL.
84 *
85 * Extra notes for generational GC:
86 *
87 * Each generation has a static object list associated with it. When
88 * collecting generations up to N, we treat the static object lists
89 * from generations > N as roots.
90 *
91 * We build up a static object list while collecting generations 0..N,
92 * which is then appended to the static object list of generation N+1.
93 */
94
95 /* N is the oldest generation being collected, where the generations
96 * are numbered starting at 0. A major GC (indicated by the major_gc
97 * flag) is when we're collecting all generations. We only attempt to
98 * deal with static objects and GC CAFs when doing a major GC.
99 */
100 nat N;
101 rtsBool major_gc;
102
103 /* Data used for allocation area sizing.
104 */
105 static lnat g0_pcnt_kept = 30; // percentage of g0 live at last minor GC
106
107 /* Mut-list stats */
108 #ifdef DEBUG
109 nat mutlist_MUTVARS,
110 mutlist_MUTARRS,
111 mutlist_MVARS,
112 mutlist_OTHERS;
113 #endif
114
115 /* Thread-local data for each GC thread
116 */
117 gc_thread **gc_threads = NULL;
118
119 #if !defined(THREADED_RTS)
120 StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(gen_workspace)];
121 #endif
122
123 // Number of threads running in *this* GC. Affects how many
124 // step->todos[] lists we have to look in to find work.
125 nat n_gc_threads;
126
127 // For stats:
128 long copied; // *words* copied & scavenged during this GC
129
130 rtsBool work_stealing;
131
132 DECLARE_GCT
133
134 /* -----------------------------------------------------------------------------
135 Static function declarations
136 -------------------------------------------------------------------------- */
137
138 static void mark_root (void *user, StgClosure **root);
139 static void zero_static_object_list (StgClosure* first_static);
140 static nat initialise_N (rtsBool force_major_gc);
141 static void prepare_collected_gen (generation *gen);
142 static void prepare_uncollected_gen (generation *gen);
143 static void init_gc_thread (gc_thread *t);
144 static void resize_generations (void);
145 static void resize_nursery (void);
146 static void start_gc_threads (void);
147 static void scavenge_until_all_done (void);
148 static StgWord inc_running (void);
149 static StgWord dec_running (void);
150 static void wakeup_gc_threads (nat me);
151 static void shutdown_gc_threads (nat me);
152 static void collect_gct_blocks (void);
153
154 #if 0 && defined(DEBUG)
155 static void gcCAFs (void);
156 #endif
157
158 /* -----------------------------------------------------------------------------
159 The mark stack.
160 -------------------------------------------------------------------------- */
161
162 bdescr *mark_stack_top_bd; // topmost block in the mark stack
163 bdescr *mark_stack_bd; // current block in the mark stack
164 StgPtr mark_sp; // pointer to the next unallocated mark stack entry
165
166 /* -----------------------------------------------------------------------------
167 GarbageCollect: the main entry point to the garbage collector.
168
169 Locks held: all capabilities are held throughout GarbageCollect().
170 -------------------------------------------------------------------------- */
171
172 void
173 GarbageCollect (rtsBool force_major_gc,
174 nat gc_type USED_IF_THREADS,
175 Capability *cap)
176 {
177 bdescr *bd;
178 generation *gen;
179 lnat live_blocks, live_words, allocated, max_copied, avg_copied;
180 gc_thread *saved_gct;
181 nat g, n;
182
183 // necessary if we stole a callee-saves register for gct:
184 saved_gct = gct;
185
186 #ifdef PROFILING
187 CostCentreStack *prev_CCS;
188 #endif
189
190 ACQUIRE_SM_LOCK;
191
192 #if defined(RTS_USER_SIGNALS)
193 if (RtsFlags.MiscFlags.install_signal_handlers) {
194 // block signals
195 blockUserSignals();
196 }
197 #endif
198
199 ASSERT(sizeof(gen_workspace) == 16 * sizeof(StgWord));
200 // otherwise adjust the padding in gen_workspace.
201
202 // this is the main thread
203 SET_GCT(gc_threads[cap->no]);
204
205 // tell the stats department that we've started a GC
206 stat_startGC(gct);
207
208 // lock the StablePtr table
209 stablePtrPreGC();
210
211 #ifdef DEBUG
212 mutlist_MUTVARS = 0;
213 mutlist_MUTARRS = 0;
214 mutlist_OTHERS = 0;
215 #endif
216
217 // attribute any costs to CCS_GC
218 #ifdef PROFILING
219 prev_CCS = CCCS;
220 CCCS = CCS_GC;
221 #endif
222
223 /* Approximate how much we allocated.
224 * Todo: only when generating stats?
225 */
226 allocated = calcAllocated(rtsFalse/* don't count the nursery yet */);
227
228 /* Figure out which generation to collect
229 */
230 n = initialise_N(force_major_gc);
231
232 #if defined(THREADED_RTS)
233 work_stealing = RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
234 N >= RtsFlags.ParFlags.parGcLoadBalancingGen;
235 // It's not always a good idea to do load balancing in parallel
236 // GC. In particular, for a parallel program we don't want to
237 // lose locality by moving cached data into another CPU's cache
238 // (this effect can be quite significant).
239 //
240 // We could have a more complex way to deterimine whether to do
241 // work stealing or not, e.g. it might be a good idea to do it
242 // if the heap is big. For now, we just turn it on or off with
243 // a flag.
244 #endif
245
246 /* Start threads, so they can be spinning up while we finish initialisation.
247 */
248 start_gc_threads();
249
250 #if defined(THREADED_RTS)
251 /* How many threads will be participating in this GC?
252 * We don't try to parallelise minor GCs (unless the user asks for
253 * it with +RTS -gn0), or mark/compact/sweep GC.
254 */
255 if (gc_type == PENDING_GC_PAR) {
256 n_gc_threads = RtsFlags.ParFlags.nNodes;
257 } else {
258 n_gc_threads = 1;
259 }
260 #else
261 n_gc_threads = 1;
262 #endif
263
264 debugTrace(DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
265 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
266
267 #ifdef RTS_GTK_FRONTPANEL
268 if (RtsFlags.GcFlags.frontpanel) {
269 updateFrontPanelBeforeGC(N);
270 }
271 #endif
272
273 #ifdef DEBUG
274 // check for memory leaks if DEBUG is on
275 memInventory(DEBUG_gc);
276 #endif
277
278 // check sanity *before* GC
279 IF_DEBUG(sanity, checkSanity(rtsFalse /* before GC */, major_gc));
280
281 // Initialise all the generations/steps that we're collecting.
282 for (g = 0; g <= N; g++) {
283 prepare_collected_gen(&generations[g]);
284 }
285 // Initialise all the generations/steps that we're *not* collecting.
286 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
287 prepare_uncollected_gen(&generations[g]);
288 }
289
290 // Prepare this gc_thread
291 init_gc_thread(gct);
292
293 /* Allocate a mark stack if we're doing a major collection.
294 */
295 if (major_gc && oldest_gen->mark) {
296 mark_stack_bd = allocBlock();
297 mark_stack_top_bd = mark_stack_bd;
298 mark_stack_bd->link = NULL;
299 mark_stack_bd->u.back = NULL;
300 mark_sp = mark_stack_bd->start;
301 } else {
302 mark_stack_bd = NULL;
303 mark_stack_top_bd = NULL;
304 mark_sp = NULL;
305 }
306
307 /* -----------------------------------------------------------------------
308 * follow all the roots that we know about:
309 */
310
311 // the main thread is running: this prevents any other threads from
312 // exiting prematurely, so we can start them now.
313 // NB. do this after the mutable lists have been saved above, otherwise
314 // the other GC threads will be writing into the old mutable lists.
315 inc_running();
316 wakeup_gc_threads(gct->thread_index);
317
318 traceEventGcWork(gct->cap);
319
320 // scavenge the capability-private mutable lists. This isn't part
321 // of markSomeCapabilities() because markSomeCapabilities() can only
322 // call back into the GC via mark_root() (due to the gct register
323 // variable).
324 if (n_gc_threads == 1) {
325 for (n = 0; n < n_capabilities; n++) {
326 #if defined(THREADED_RTS)
327 scavenge_capability_mut_Lists1(&capabilities[n]);
328 #else
329 scavenge_capability_mut_lists(&capabilities[n]);
330 #endif
331 }
332 } else {
333 scavenge_capability_mut_lists(gct->cap);
334 }
335
336 // follow roots from the CAF list (used by GHCi)
337 gct->evac_gen_no = 0;
338 markCAFs(mark_root, gct);
339
340 // follow all the roots that the application knows about.
341 gct->evac_gen_no = 0;
342 if (n_gc_threads == 1) {
343 for (n = 0; n < n_capabilities; n++) {
344 markCapability(mark_root, gct, &capabilities[n],
345 rtsTrue/*don't mark sparks*/);
346 }
347 } else {
348 markCapability(mark_root, gct, cap, rtsTrue/*don't mark sparks*/);
349 }
350
351 markScheduler(mark_root, gct);
352
353 #if defined(RTS_USER_SIGNALS)
354 // mark the signal handlers (signals should be already blocked)
355 markSignalHandlers(mark_root, gct);
356 #endif
357
358 // Mark the weak pointer list, and prepare to detect dead weak pointers.
359 markWeakPtrList();
360 initWeakForGC();
361
362 // Mark the stable pointer table.
363 markStablePtrTable(mark_root, gct);
364
365 /* -------------------------------------------------------------------------
366 * Repeatedly scavenge all the areas we know about until there's no
367 * more scavenging to be done.
368 */
369 for (;;)
370 {
371 scavenge_until_all_done();
372 // The other threads are now stopped. We might recurse back to
373 // here, but from now on this is the only thread.
374
375 // must be last... invariant is that everything is fully
376 // scavenged at this point.
377 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
378 inc_running();
379 continue;
380 }
381
382 // If we get to here, there's really nothing left to do.
383 break;
384 }
385
386 shutdown_gc_threads(gct->thread_index);
387
388 // Now see which stable names are still alive.
389 gcStablePtrTable();
390
391 #ifdef THREADED_RTS
392 if (n_gc_threads == 1) {
393 for (n = 0; n < n_capabilities; n++) {
394 pruneSparkQueue(&capabilities[n]);
395 }
396 } else {
397 pruneSparkQueue(gct->cap);
398 }
399 #endif
400
401 #ifdef PROFILING
402 // We call processHeapClosureForDead() on every closure destroyed during
403 // the current garbage collection, so we invoke LdvCensusForDead().
404 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
405 || RtsFlags.ProfFlags.bioSelector != NULL)
406 LdvCensusForDead(N);
407 #endif
408
409 // NO MORE EVACUATION AFTER THIS POINT!
410
411 // Two-space collector: free the old to-space.
412 // g0->old_blocks is the old nursery
413 // g0->blocks is to-space from the previous GC
414 if (RtsFlags.GcFlags.generations == 1) {
415 if (g0->blocks != NULL) {
416 freeChain(g0->blocks);
417 g0->blocks = NULL;
418 }
419 }
420
421 // Finally: compact or sweep the oldest generation.
422 if (major_gc && oldest_gen->mark) {
423 if (oldest_gen->compact)
424 compact(gct->scavenged_static_objects);
425 else
426 sweep(oldest_gen);
427 }
428
429 copied = 0;
430 max_copied = 0;
431 avg_copied = 0;
432 {
433 nat i;
434 for (i=0; i < n_gc_threads; i++) {
435 if (n_gc_threads > 1) {
436 debugTrace(DEBUG_gc,"thread %d:", i);
437 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
438 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
439 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
440 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
441 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
442 }
443 copied += gc_threads[i]->copied;
444 max_copied = stg_max(gc_threads[i]->copied, max_copied);
445 }
446 if (n_gc_threads == 1) {
447 max_copied = 0;
448 avg_copied = 0;
449 } else {
450 avg_copied = copied;
451 }
452 }
453
454 // Run through all the generations/steps and tidy up.
455 // We're going to:
456 // - count the amount of "live" data (live_words, live_blocks)
457 // - count the amount of "copied" data in this GC (copied)
458 // - free from-space
459 // - make to-space the new from-space (set BF_EVACUATED on all blocks)
460 //
461 live_words = 0;
462 live_blocks = 0;
463
464 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
465
466 if (g == N) {
467 generations[g].collections++; // for stats
468 if (n_gc_threads > 1) generations[g].par_collections++;
469 }
470
471 // Count the mutable list as bytes "copied" for the purposes of
472 // stats. Every mutable list is copied during every GC.
473 if (g > 0) {
474 nat mut_list_size = 0;
475 for (n = 0; n < n_capabilities; n++) {
476 mut_list_size += countOccupied(capabilities[n].mut_lists[g]);
477 }
478 copied += mut_list_size;
479
480 debugTrace(DEBUG_gc,
481 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
482 (unsigned long)(mut_list_size * sizeof(W_)),
483 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
484 }
485
486 bdescr *next, *prev;
487 gen = &generations[g];
488
489 // for generations we collected...
490 if (g <= N) {
491
492 /* free old memory and shift to-space into from-space for all
493 * the collected steps (except the allocation area). These
494 * freed blocks will probaby be quickly recycled.
495 */
496 if (gen->mark)
497 {
498 // tack the new blocks on the end of the existing blocks
499 if (gen->old_blocks != NULL) {
500
501 prev = NULL;
502 for (bd = gen->old_blocks; bd != NULL; bd = next) {
503
504 next = bd->link;
505
506 if (!(bd->flags & BF_MARKED))
507 {
508 if (prev == NULL) {
509 gen->old_blocks = next;
510 } else {
511 prev->link = next;
512 }
513 freeGroup(bd);
514 gen->n_old_blocks--;
515 }
516 else
517 {
518 gen->n_words += bd->free - bd->start;
519
520 // NB. this step might not be compacted next
521 // time, so reset the BF_MARKED flags.
522 // They are set before GC if we're going to
523 // compact. (search for BF_MARKED above).
524 bd->flags &= ~BF_MARKED;
525
526 // between GCs, all blocks in the heap except
527 // for the nursery have the BF_EVACUATED flag set.
528 bd->flags |= BF_EVACUATED;
529
530 prev = bd;
531 }
532 }
533
534 if (prev != NULL) {
535 prev->link = gen->blocks;
536 gen->blocks = gen->old_blocks;
537 }
538 }
539 // add the new blocks to the block tally
540 gen->n_blocks += gen->n_old_blocks;
541 ASSERT(countBlocks(gen->blocks) == gen->n_blocks);
542 ASSERT(countOccupied(gen->blocks) == gen->n_words);
543 }
544 else // not copacted
545 {
546 freeChain(gen->old_blocks);
547 }
548
549 gen->old_blocks = NULL;
550 gen->n_old_blocks = 0;
551
552 /* LARGE OBJECTS. The current live large objects are chained on
553 * scavenged_large, having been moved during garbage
554 * collection from large_objects. Any objects left on the
555 * large_objects list are therefore dead, so we free them here.
556 */
557 freeChain(gen->large_objects);
558 gen->large_objects = gen->scavenged_large_objects;
559 gen->n_large_blocks = gen->n_scavenged_large_blocks;
560 gen->n_new_large_words = 0;
561 }
562 else // for generations > N
563 {
564 /* For older generations, we need to append the
565 * scavenged_large_object list (i.e. large objects that have been
566 * promoted during this GC) to the large_object list for that step.
567 */
568 for (bd = gen->scavenged_large_objects; bd; bd = next) {
569 next = bd->link;
570 dbl_link_onto(bd, &gen->large_objects);
571 }
572
573 // add the new blocks we promoted during this GC
574 gen->n_large_blocks += gen->n_scavenged_large_blocks;
575 }
576
577 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
578
579 gen->scavenged_large_objects = NULL;
580 gen->n_scavenged_large_blocks = 0;
581
582 // Count "live" data
583 live_words += genLiveWords(gen);
584 live_blocks += genLiveBlocks(gen);
585
586 // add in the partial blocks in the gen_workspaces, but ignore gen 0
587 // if this is a local GC (we can't count another capability's part_list)
588 {
589 nat i;
590 for (i = 0; i < n_capabilities; i++) {
591 live_words += gcThreadLiveWords(i, gen->no);
592 live_blocks += gcThreadLiveBlocks(i, gen->no);
593 }
594 }
595 } // for all generations
596
597 // update the max size of older generations after a major GC
598 resize_generations();
599
600 // Free the mark stack.
601 if (mark_stack_top_bd != NULL) {
602 debugTrace(DEBUG_gc, "mark stack: %d blocks",
603 countBlocks(mark_stack_top_bd));
604 freeChain(mark_stack_top_bd);
605 }
606
607 // Free any bitmaps.
608 for (g = 0; g <= N; g++) {
609 gen = &generations[g];
610 if (gen->bitmap != NULL) {
611 freeGroup(gen->bitmap);
612 gen->bitmap = NULL;
613 }
614 }
615
616 // Reset the nursery: make the blocks empty
617 allocated += clearNurseries();
618
619 resize_nursery();
620
621 resetNurseries();
622
623 // mark the garbage collected CAFs as dead
624 #if 0 && defined(DEBUG) // doesn't work at the moment
625 if (major_gc) { gcCAFs(); }
626 #endif
627
628 #ifdef PROFILING
629 // resetStaticObjectForRetainerProfiling() must be called before
630 // zeroing below.
631 if (n_gc_threads > 1) {
632 barf("profiling is currently broken with multi-threaded GC");
633 // ToDo: fix the gct->scavenged_static_objects below
634 }
635 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
636 #endif
637
638 // zero the scavenged static object list
639 if (major_gc) {
640 nat i;
641 if (n_gc_threads == 1) {
642 zero_static_object_list(gct->scavenged_static_objects);
643 } else {
644 for (i = 0; i < n_gc_threads; i++) {
645 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
646 }
647 }
648 }
649
650 // Update the stable pointer hash table.
651 updateStablePtrTable(major_gc);
652
653 // unlock the StablePtr table. Must be before scheduleFinalizers(),
654 // because a finalizer may call hs_free_fun_ptr() or
655 // hs_free_stable_ptr(), both of which access the StablePtr table.
656 stablePtrPostGC();
657
658 // Start any pending finalizers. Must be after
659 // updateStablePtrTable() and stablePtrPostGC() (see #4221).
660 RELEASE_SM_LOCK;
661 scheduleFinalizers(cap, old_weak_ptr_list);
662 ACQUIRE_SM_LOCK;
663
664 // check sanity after GC
665 // before resurrectThreads(), because that might overwrite some
666 // closures, which will cause problems with THREADED where we don't
667 // fill slop.
668 IF_DEBUG(sanity, checkSanity(rtsTrue /* after GC */, major_gc));
669
670 // send exceptions to any threads which were about to die
671 RELEASE_SM_LOCK;
672 resurrectThreads(resurrected_threads);
673 ACQUIRE_SM_LOCK;
674
675 if (major_gc) {
676 nat need, got;
677 need = BLOCKS_TO_MBLOCKS(n_alloc_blocks);
678 got = mblocks_allocated;
679 /* If the amount of data remains constant, next major GC we'll
680 require (F+1)*need. We leave (F+2)*need in order to reduce
681 repeated deallocation and reallocation. */
682 need = (RtsFlags.GcFlags.oldGenFactor + 2) * need;
683 if (got > need) {
684 returnMemoryToOS(got - need);
685 }
686 }
687
688 // extra GC trace info
689 IF_DEBUG(gc, statDescribeGens());
690
691 #ifdef DEBUG
692 // symbol-table based profiling
693 /* heapCensus(to_blocks); */ /* ToDo */
694 #endif
695
696 // restore enclosing cost centre
697 #ifdef PROFILING
698 CCCS = prev_CCS;
699 #endif
700
701 #ifdef DEBUG
702 // check for memory leaks if DEBUG is on
703 memInventory(DEBUG_gc);
704 #endif
705
706 #ifdef RTS_GTK_FRONTPANEL
707 if (RtsFlags.GcFlags.frontpanel) {
708 updateFrontPanelAfterGC( N, live );
709 }
710 #endif
711
712 // ok, GC over: tell the stats department what happened.
713 stat_endGC(gct, allocated, live_words,
714 copied, N, max_copied, avg_copied,
715 live_blocks * BLOCK_SIZE_W - live_words /* slop */);
716
717 // Guess which generation we'll collect *next* time
718 initialise_N(force_major_gc);
719
720 #if defined(RTS_USER_SIGNALS)
721 if (RtsFlags.MiscFlags.install_signal_handlers) {
722 // unblock signals again
723 unblockUserSignals();
724 }
725 #endif
726
727 RELEASE_SM_LOCK;
728
729 SET_GCT(saved_gct);
730 }
731
732 /* -----------------------------------------------------------------------------
733 Figure out which generation to collect, initialise N and major_gc.
734
735 Also returns the total number of blocks in generations that will be
736 collected.
737 -------------------------------------------------------------------------- */
738
739 static nat
740 initialise_N (rtsBool force_major_gc)
741 {
742 int g;
743 nat blocks, blocks_total;
744
745 blocks = 0;
746 blocks_total = 0;
747
748 if (force_major_gc) {
749 N = RtsFlags.GcFlags.generations - 1;
750 } else {
751 N = 0;
752 }
753
754 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
755
756 blocks = generations[g].n_words / BLOCK_SIZE_W
757 + generations[g].n_large_blocks;
758
759 if (blocks >= generations[g].max_blocks) {
760 N = stg_max(N,g);
761 }
762 if ((nat)g <= N) {
763 blocks_total += blocks;
764 }
765 }
766
767 blocks_total += countNurseryBlocks();
768
769 major_gc = (N == RtsFlags.GcFlags.generations-1);
770 return blocks_total;
771 }
772
773 /* -----------------------------------------------------------------------------
774 Initialise the gc_thread structures.
775 -------------------------------------------------------------------------- */
776
777 #define GC_THREAD_INACTIVE 0
778 #define GC_THREAD_STANDING_BY 1
779 #define GC_THREAD_RUNNING 2
780 #define GC_THREAD_WAITING_TO_CONTINUE 3
781
782 static void
783 new_gc_thread (nat n, gc_thread *t)
784 {
785 nat g;
786 gen_workspace *ws;
787
788 t->cap = &capabilities[n];
789
790 #ifdef THREADED_RTS
791 t->id = 0;
792 initSpinLock(&t->gc_spin);
793 initSpinLock(&t->mut_spin);
794 ACQUIRE_SPIN_LOCK(&t->gc_spin);
795 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
796 // thread to start up, see wakeup_gc_threads
797 #endif
798
799 t->thread_index = n;
800 t->free_blocks = NULL;
801 t->gc_count = 0;
802
803 init_gc_thread(t);
804
805 #ifdef USE_PAPI
806 t->papi_events = -1;
807 #endif
808
809 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
810 {
811 ws = &t->gens[g];
812 ws->gen = &generations[g];
813 ASSERT(g == ws->gen->no);
814 ws->my_gct = t;
815
816 // We want to call
817 // alloc_todo_block(ws,0);
818 // but can't, because it uses gct which isn't set up at this point.
819 // Hence, allocate a block for todo_bd manually:
820 {
821 bdescr *bd = allocBlock(); // no lock, locks aren't initialised yet
822 initBdescr(bd, ws->gen, ws->gen->to);
823 bd->flags = BF_EVACUATED;
824 bd->u.scan = bd->free = bd->start;
825
826 ws->todo_bd = bd;
827 ws->todo_free = bd->free;
828 ws->todo_lim = bd->start + BLOCK_SIZE_W;
829 }
830
831 ws->todo_q = newWSDeque(128);
832 ws->todo_overflow = NULL;
833 ws->n_todo_overflow = 0;
834 ws->todo_large_objects = NULL;
835
836 ws->part_list = NULL;
837 ws->n_part_blocks = 0;
838
839 ws->scavd_list = NULL;
840 ws->n_scavd_blocks = 0;
841 }
842 }
843
844
845 void
846 initGcThreads (void)
847 {
848 if (gc_threads == NULL) {
849 #if defined(THREADED_RTS)
850 nat i;
851 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
852 sizeof(gc_thread*),
853 "alloc_gc_threads");
854
855 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
856 gc_threads[i] =
857 stgMallocBytes(sizeof(gc_thread) +
858 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
859 "alloc_gc_threads");
860
861 new_gc_thread(i, gc_threads[i]);
862 }
863 #else
864 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
865 gc_threads[0] = gct;
866 new_gc_thread(0,gc_threads[0]);
867 #endif
868 }
869 }
870
871 void
872 freeGcThreads (void)
873 {
874 nat g;
875 if (gc_threads != NULL) {
876 #if defined(THREADED_RTS)
877 nat i;
878 for (i = 0; i < n_capabilities; i++) {
879 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
880 {
881 freeWSDeque(gc_threads[i]->gens[g].todo_q);
882 }
883 stgFree (gc_threads[i]);
884 }
885 stgFree (gc_threads);
886 #else
887 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
888 {
889 freeWSDeque(gc_threads[0]->gens[g].todo_q);
890 }
891 stgFree (gc_threads);
892 #endif
893 gc_threads = NULL;
894 }
895 }
896
897 /* ----------------------------------------------------------------------------
898 Start GC threads
899 ------------------------------------------------------------------------- */
900
901 static volatile StgWord gc_running_threads;
902
903 static StgWord
904 inc_running (void)
905 {
906 StgWord new;
907 new = atomic_inc(&gc_running_threads);
908 ASSERT(new <= n_gc_threads);
909 return new;
910 }
911
912 static StgWord
913 dec_running (void)
914 {
915 ASSERT(gc_running_threads != 0);
916 return atomic_dec(&gc_running_threads);
917 }
918
919 static rtsBool
920 any_work (void)
921 {
922 int g;
923 gen_workspace *ws;
924
925 gct->any_work++;
926
927 write_barrier();
928
929 // scavenge objects in compacted generation
930 if (mark_stack_bd != NULL && !mark_stack_empty()) {
931 return rtsTrue;
932 }
933
934 // Check for global work in any step. We don't need to check for
935 // local work, because we have already exited scavenge_loop(),
936 // which means there is no local work for this thread.
937 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
938 ws = &gct->gens[g];
939 if (ws->todo_large_objects) return rtsTrue;
940 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
941 if (ws->todo_overflow) return rtsTrue;
942 }
943
944 #if defined(THREADED_RTS)
945 if (work_stealing) {
946 nat n;
947 // look for work to steal
948 for (n = 0; n < n_gc_threads; n++) {
949 if (n == gct->thread_index) continue;
950 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
951 ws = &gc_threads[n]->gens[g];
952 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
953 }
954 }
955 }
956 #endif
957
958 gct->no_work++;
959 #if defined(THREADED_RTS)
960 yieldThread();
961 #endif
962
963 return rtsFalse;
964 }
965
966 static void
967 scavenge_until_all_done (void)
968 {
969 nat r;
970
971
972 loop:
973 #if defined(THREADED_RTS)
974 if (n_gc_threads > 1) {
975 scavenge_loop();
976 } else {
977 scavenge_loop1();
978 }
979 #else
980 scavenge_loop();
981 #endif
982
983 collect_gct_blocks();
984
985 // scavenge_loop() only exits when there's no work to do
986 r = dec_running();
987
988 traceEventGcIdle(gct->cap);
989
990 debugTrace(DEBUG_gc, "%d GC threads still running", r);
991
992 while (gc_running_threads != 0) {
993 // usleep(1);
994 if (any_work()) {
995 inc_running();
996 traceEventGcWork(gct->cap);
997 goto loop;
998 }
999 // any_work() does not remove the work from the queue, it
1000 // just checks for the presence of work. If we find any,
1001 // then we increment gc_running_threads and go back to
1002 // scavenge_loop() to perform any pending work.
1003 }
1004
1005 traceEventGcDone(gct->cap);
1006 }
1007
1008 #if defined(THREADED_RTS)
1009
1010 void
1011 gcWorkerThread (Capability *cap)
1012 {
1013 gc_thread *saved_gct;
1014
1015 // necessary if we stole a callee-saves register for gct:
1016 saved_gct = gct;
1017
1018 gct = gc_threads[cap->no];
1019 gct->id = osThreadId();
1020
1021 stat_gcWorkerThreadStart(gct);
1022
1023 // Wait until we're told to wake up
1024 RELEASE_SPIN_LOCK(&gct->mut_spin);
1025 gct->wakeup = GC_THREAD_STANDING_BY;
1026 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1027 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1028
1029 #ifdef USE_PAPI
1030 // start performance counters in this thread...
1031 if (gct->papi_events == -1) {
1032 papi_init_eventset(&gct->papi_events);
1033 }
1034 papi_thread_start_gc1_count(gct->papi_events);
1035 #endif
1036
1037 init_gc_thread(gct);
1038
1039 traceEventGcWork(gct->cap);
1040
1041 // Every thread evacuates some roots.
1042 gct->evac_gen_no = 0;
1043 markCapability(mark_root, gct, cap, rtsTrue/*prune sparks*/);
1044 scavenge_capability_mut_lists(cap);
1045
1046 scavenge_until_all_done();
1047
1048 #ifdef THREADED_RTS
1049 // Now that the whole heap is marked, we discard any sparks that
1050 // were found to be unreachable. The main GC thread is currently
1051 // marking heap reachable via weak pointers, so it is
1052 // non-deterministic whether a spark will be retained if it is
1053 // only reachable via weak pointers. To fix this problem would
1054 // require another GC barrier, which is too high a price.
1055 pruneSparkQueue(cap);
1056 #endif
1057
1058 #ifdef USE_PAPI
1059 // count events in this thread towards the GC totals
1060 papi_thread_stop_gc1_count(gct->papi_events);
1061 #endif
1062
1063 // Wait until we're told to continue
1064 RELEASE_SPIN_LOCK(&gct->gc_spin);
1065 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1066 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1067 gct->thread_index);
1068 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1069 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1070
1071 // record the time spent doing GC in the Task structure
1072 stat_gcWorkerThreadDone(gct);
1073
1074 SET_GCT(saved_gct);
1075 }
1076
1077 #endif
1078
1079 #if defined(THREADED_RTS)
1080
1081 void
1082 waitForGcThreads (Capability *cap USED_IF_THREADS)
1083 {
1084 const nat n_threads = RtsFlags.ParFlags.nNodes;
1085 const nat me = cap->no;
1086 nat i, j;
1087 rtsBool retry = rtsTrue;
1088
1089 while(retry) {
1090 for (i=0; i < n_threads; i++) {
1091 if (i == me) continue;
1092 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1093 prodCapability(&capabilities[i], cap->running_task);
1094 }
1095 }
1096 for (j=0; j < 10; j++) {
1097 retry = rtsFalse;
1098 for (i=0; i < n_threads; i++) {
1099 if (i == me) continue;
1100 write_barrier();
1101 setContextSwitches();
1102 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1103 retry = rtsTrue;
1104 }
1105 }
1106 if (!retry) break;
1107 yieldThread();
1108 }
1109 }
1110 }
1111
1112 #endif // THREADED_RTS
1113
1114 static void
1115 start_gc_threads (void)
1116 {
1117 #if defined(THREADED_RTS)
1118 gc_running_threads = 0;
1119 #endif
1120 }
1121
1122 static void
1123 wakeup_gc_threads (nat me USED_IF_THREADS)
1124 {
1125 #if defined(THREADED_RTS)
1126 nat i;
1127
1128 if (n_gc_threads == 1) return;
1129
1130 for (i=0; i < n_gc_threads; i++) {
1131 if (i == me) continue;
1132 inc_running();
1133 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1134 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1135
1136 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1137 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1138 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1139 }
1140 #endif
1141 }
1142
1143 // After GC is complete, we must wait for all GC threads to enter the
1144 // standby state, otherwise they may still be executing inside
1145 // any_work(), and may even remain awake until the next GC starts.
1146 static void
1147 shutdown_gc_threads (nat me USED_IF_THREADS)
1148 {
1149 #if defined(THREADED_RTS)
1150 nat i;
1151
1152 if (n_gc_threads == 1) return;
1153
1154 for (i=0; i < n_gc_threads; i++) {
1155 if (i == me) continue;
1156 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1157 }
1158 #endif
1159 }
1160
1161 #if defined(THREADED_RTS)
1162 void
1163 releaseGCThreads (Capability *cap USED_IF_THREADS)
1164 {
1165 const nat n_threads = RtsFlags.ParFlags.nNodes;
1166 const nat me = cap->no;
1167 nat i;
1168 for (i=0; i < n_threads; i++) {
1169 if (i == me) continue;
1170 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1171 barf("releaseGCThreads");
1172
1173 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1174 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1175 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1176 }
1177 }
1178 #endif
1179
1180 /* ----------------------------------------------------------------------------
1181 Initialise a generation that is to be collected
1182 ------------------------------------------------------------------------- */
1183
1184 static void
1185 prepare_collected_gen (generation *gen)
1186 {
1187 nat i, g, n;
1188 gen_workspace *ws;
1189 bdescr *bd, *next;
1190
1191 // Throw away the current mutable list. Invariant: the mutable
1192 // list always has at least one block; this means we can avoid a
1193 // check for NULL in recordMutable().
1194 g = gen->no;
1195 if (g != 0) {
1196 for (i = 0; i < n_capabilities; i++) {
1197 freeChain(capabilities[i].mut_lists[g]);
1198 capabilities[i].mut_lists[g] = allocBlock();
1199 }
1200 }
1201
1202 gen = &generations[g];
1203 ASSERT(gen->no == g);
1204
1205 // we'll construct a new list of threads in this step
1206 // during GC, throw away the current list.
1207 gen->old_threads = gen->threads;
1208 gen->threads = END_TSO_QUEUE;
1209
1210 // deprecate the existing blocks
1211 gen->old_blocks = gen->blocks;
1212 gen->n_old_blocks = gen->n_blocks;
1213 gen->blocks = NULL;
1214 gen->n_blocks = 0;
1215 gen->n_words = 0;
1216 gen->live_estimate = 0;
1217
1218 // initialise the large object queues.
1219 ASSERT(gen->scavenged_large_objects == NULL);
1220 ASSERT(gen->n_scavenged_large_blocks == 0);
1221
1222 // grab all the partial blocks stashed in the gc_thread workspaces and
1223 // move them to the old_blocks list of this gen.
1224 for (n = 0; n < n_capabilities; n++) {
1225 ws = &gc_threads[n]->gens[gen->no];
1226
1227 for (bd = ws->part_list; bd != NULL; bd = next) {
1228 next = bd->link;
1229 bd->link = gen->old_blocks;
1230 gen->old_blocks = bd;
1231 gen->n_old_blocks += bd->blocks;
1232 }
1233 ws->part_list = NULL;
1234 ws->n_part_blocks = 0;
1235
1236 ASSERT(ws->scavd_list == NULL);
1237 ASSERT(ws->n_scavd_blocks == 0);
1238
1239 if (ws->todo_free != ws->todo_bd->start) {
1240 ws->todo_bd->free = ws->todo_free;
1241 ws->todo_bd->link = gen->old_blocks;
1242 gen->old_blocks = ws->todo_bd;
1243 gen->n_old_blocks += ws->todo_bd->blocks;
1244 alloc_todo_block(ws,0); // always has one block.
1245 }
1246 }
1247
1248 // mark the small objects as from-space
1249 for (bd = gen->old_blocks; bd; bd = bd->link) {
1250 bd->flags &= ~BF_EVACUATED;
1251 }
1252
1253 // mark the large objects as from-space
1254 for (bd = gen->large_objects; bd; bd = bd->link) {
1255 bd->flags &= ~BF_EVACUATED;
1256 }
1257
1258 // for a compacted generation, we need to allocate the bitmap
1259 if (gen->mark) {
1260 nat bitmap_size; // in bytes
1261 bdescr *bitmap_bdescr;
1262 StgWord *bitmap;
1263
1264 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1265
1266 if (bitmap_size > 0) {
1267 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1268 / BLOCK_SIZE);
1269 gen->bitmap = bitmap_bdescr;
1270 bitmap = bitmap_bdescr->start;
1271
1272 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1273 bitmap_size, bitmap);
1274
1275 // don't forget to fill it with zeros!
1276 memset(bitmap, 0, bitmap_size);
1277
1278 // For each block in this step, point to its bitmap from the
1279 // block descriptor.
1280 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1281 bd->u.bitmap = bitmap;
1282 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1283
1284 // Also at this point we set the BF_MARKED flag
1285 // for this block. The invariant is that
1286 // BF_MARKED is always unset, except during GC
1287 // when it is set on those blocks which will be
1288 // compacted.
1289 if (!(bd->flags & BF_FRAGMENTED)) {
1290 bd->flags |= BF_MARKED;
1291 }
1292
1293 // BF_SWEPT should be marked only for blocks that are being
1294 // collected in sweep()
1295 bd->flags &= ~BF_SWEPT;
1296 }
1297 }
1298 }
1299 }
1300
1301
1302 /* ----------------------------------------------------------------------------
1303 Save the mutable lists in saved_mut_lists
1304 ------------------------------------------------------------------------- */
1305
1306 static void
1307 stash_mut_list (Capability *cap, nat gen_no)
1308 {
1309 cap->saved_mut_lists[gen_no] = cap->mut_lists[gen_no];
1310 cap->mut_lists[gen_no] = allocBlock_sync();
1311 }
1312
1313 /* ----------------------------------------------------------------------------
1314 Initialise a generation that is *not* to be collected
1315 ------------------------------------------------------------------------- */
1316
1317 static void
1318 prepare_uncollected_gen (generation *gen)
1319 {
1320 nat i;
1321
1322
1323 ASSERT(gen->no > 0);
1324
1325 // save the current mutable lists for this generation, and
1326 // allocate a fresh block for each one. We'll traverse these
1327 // mutable lists as roots early on in the GC.
1328 for (i = 0; i < n_capabilities; i++) {
1329 stash_mut_list(&capabilities[i], gen->no);
1330 }
1331
1332 ASSERT(gen->scavenged_large_objects == NULL);
1333 ASSERT(gen->n_scavenged_large_blocks == 0);
1334 }
1335
1336 /* -----------------------------------------------------------------------------
1337 Collect the completed blocks from a GC thread and attach them to
1338 the generation.
1339 -------------------------------------------------------------------------- */
1340
1341 static void
1342 collect_gct_blocks (void)
1343 {
1344 nat g;
1345 gen_workspace *ws;
1346 bdescr *bd, *prev;
1347
1348 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1349 ws = &gct->gens[g];
1350
1351 // there may still be a block attached to ws->todo_bd;
1352 // leave it there to use next time.
1353
1354 if (ws->scavd_list != NULL) {
1355 ACQUIRE_SPIN_LOCK(&ws->gen->sync);
1356
1357 ASSERT(gct->scan_bd == NULL);
1358 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
1359
1360 prev = NULL;
1361 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
1362 ws->gen->n_words += bd->free - bd->start;
1363 prev = bd;
1364 }
1365 if (prev != NULL) {
1366 prev->link = ws->gen->blocks;
1367 ws->gen->blocks = ws->scavd_list;
1368 }
1369 ws->gen->n_blocks += ws->n_scavd_blocks;
1370
1371 ws->scavd_list = NULL;
1372 ws->n_scavd_blocks = 0;
1373
1374 RELEASE_SPIN_LOCK(&ws->gen->sync);
1375 }
1376 }
1377 }
1378
1379 /* -----------------------------------------------------------------------------
1380 Initialise a gc_thread before GC
1381 -------------------------------------------------------------------------- */
1382
1383 static void
1384 init_gc_thread (gc_thread *t)
1385 {
1386 t->static_objects = END_OF_STATIC_LIST;
1387 t->scavenged_static_objects = END_OF_STATIC_LIST;
1388 t->scan_bd = NULL;
1389 t->mut_lists = t->cap->mut_lists;
1390 t->evac_gen_no = 0;
1391 t->failed_to_evac = rtsFalse;
1392 t->eager_promotion = rtsTrue;
1393 t->thunk_selector_depth = 0;
1394 t->copied = 0;
1395 t->scanned = 0;
1396 t->any_work = 0;
1397 t->no_work = 0;
1398 t->scav_find_work = 0;
1399 }
1400
1401 /* -----------------------------------------------------------------------------
1402 Function we pass to evacuate roots.
1403 -------------------------------------------------------------------------- */
1404
1405 static void
1406 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1407 {
1408 // we stole a register for gct, but this function is called from
1409 // *outside* the GC where the register variable is not in effect,
1410 // so we need to save and restore it here. NB. only call
1411 // mark_root() from the main GC thread, otherwise gct will be
1412 // incorrect.
1413 gc_thread *saved_gct;
1414 saved_gct = gct;
1415 SET_GCT(user);
1416
1417 evacuate(root);
1418
1419 SET_GCT(saved_gct);
1420 }
1421
1422 /* -----------------------------------------------------------------------------
1423 Initialising the static object & mutable lists
1424 -------------------------------------------------------------------------- */
1425
1426 static void
1427 zero_static_object_list(StgClosure* first_static)
1428 {
1429 StgClosure* p;
1430 StgClosure* link;
1431 const StgInfoTable *info;
1432
1433 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1434 info = get_itbl(p);
1435 link = *STATIC_LINK(info, p);
1436 *STATIC_LINK(info,p) = NULL;
1437 }
1438 }
1439
1440 /* ----------------------------------------------------------------------------
1441 Reset the sizes of the older generations when we do a major
1442 collection.
1443
1444 CURRENT STRATEGY: make all generations except zero the same size.
1445 We have to stay within the maximum heap size, and leave a certain
1446 percentage of the maximum heap size available to allocate into.
1447 ------------------------------------------------------------------------- */
1448
1449 static void
1450 resize_generations (void)
1451 {
1452 nat g;
1453
1454 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1455 nat live, size, min_alloc, words;
1456 const nat max = RtsFlags.GcFlags.maxHeapSize;
1457 const nat gens = RtsFlags.GcFlags.generations;
1458
1459 // live in the oldest generations
1460 if (oldest_gen->live_estimate != 0) {
1461 words = oldest_gen->live_estimate;
1462 } else {
1463 words = oldest_gen->n_words;
1464 }
1465 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1466 oldest_gen->n_large_blocks;
1467
1468 // default max size for all generations except zero
1469 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1470 RtsFlags.GcFlags.minOldGenSize);
1471
1472 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1473 RtsFlags.GcFlags.heapSizeSuggestion = size;
1474 }
1475
1476 // minimum size for generation zero
1477 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1478 RtsFlags.GcFlags.minAllocAreaSize);
1479
1480 // Auto-enable compaction when the residency reaches a
1481 // certain percentage of the maximum heap size (default: 30%).
1482 if (RtsFlags.GcFlags.compact ||
1483 (max > 0 &&
1484 oldest_gen->n_blocks >
1485 (RtsFlags.GcFlags.compactThreshold * max) / 100)) {
1486 oldest_gen->mark = 1;
1487 oldest_gen->compact = 1;
1488 // debugBelch("compaction: on\n", live);
1489 } else {
1490 oldest_gen->mark = 0;
1491 oldest_gen->compact = 0;
1492 // debugBelch("compaction: off\n", live);
1493 }
1494
1495 if (RtsFlags.GcFlags.sweep) {
1496 oldest_gen->mark = 1;
1497 }
1498
1499 // if we're going to go over the maximum heap size, reduce the
1500 // size of the generations accordingly. The calculation is
1501 // different if compaction is turned on, because we don't need
1502 // to double the space required to collect the old generation.
1503 if (max != 0) {
1504
1505 // this test is necessary to ensure that the calculations
1506 // below don't have any negative results - we're working
1507 // with unsigned values here.
1508 if (max < min_alloc) {
1509 heapOverflow();
1510 }
1511
1512 if (oldest_gen->compact) {
1513 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1514 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1515 }
1516 } else {
1517 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1518 size = (max - min_alloc) / ((gens - 1) * 2);
1519 }
1520 }
1521
1522 if (size < live) {
1523 heapOverflow();
1524 }
1525 }
1526
1527 #if 0
1528 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1529 min_alloc, size, max);
1530 #endif
1531
1532 for (g = 0; g < gens; g++) {
1533 generations[g].max_blocks = size;
1534 }
1535 }
1536 }
1537
1538 /* -----------------------------------------------------------------------------
1539 Calculate the new size of the nursery, and resize it.
1540 -------------------------------------------------------------------------- */
1541
1542 static void
1543 resize_nursery (void)
1544 {
1545 const lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1546
1547 if (RtsFlags.GcFlags.generations == 1)
1548 { // Two-space collector:
1549 nat blocks;
1550
1551 /* set up a new nursery. Allocate a nursery size based on a
1552 * function of the amount of live data (by default a factor of 2)
1553 * Use the blocks from the old nursery if possible, freeing up any
1554 * left over blocks.
1555 *
1556 * If we get near the maximum heap size, then adjust our nursery
1557 * size accordingly. If the nursery is the same size as the live
1558 * data (L), then we need 3L bytes. We can reduce the size of the
1559 * nursery to bring the required memory down near 2L bytes.
1560 *
1561 * A normal 2-space collector would need 4L bytes to give the same
1562 * performance we get from 3L bytes, reducing to the same
1563 * performance at 2L bytes.
1564 */
1565 blocks = generations[0].n_blocks;
1566
1567 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1568 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1569 RtsFlags.GcFlags.maxHeapSize )
1570 {
1571 long adjusted_blocks; // signed on purpose
1572 int pc_free;
1573
1574 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1575
1576 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1577 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1578
1579 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1580 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1581 {
1582 heapOverflow();
1583 }
1584 blocks = adjusted_blocks;
1585 }
1586 else
1587 {
1588 blocks *= RtsFlags.GcFlags.oldGenFactor;
1589 if (blocks < min_nursery)
1590 {
1591 blocks = min_nursery;
1592 }
1593 }
1594 resizeNurseries(blocks);
1595 }
1596 else // Generational collector
1597 {
1598 /*
1599 * If the user has given us a suggested heap size, adjust our
1600 * allocation area to make best use of the memory available.
1601 */
1602 if (RtsFlags.GcFlags.heapSizeSuggestion)
1603 {
1604 long blocks;
1605 const nat needed = calcNeeded(); // approx blocks needed at next GC
1606
1607 /* Guess how much will be live in generation 0 step 0 next time.
1608 * A good approximation is obtained by finding the
1609 * percentage of g0 that was live at the last minor GC.
1610 *
1611 * We have an accurate figure for the amount of copied data in
1612 * 'copied', but we must convert this to a number of blocks, with
1613 * a small adjustment for estimated slop at the end of a block
1614 * (- 10 words).
1615 */
1616 if (N == 0)
1617 {
1618 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1619 / countNurseryBlocks();
1620 }
1621
1622 /* Estimate a size for the allocation area based on the
1623 * information available. We might end up going slightly under
1624 * or over the suggested heap size, but we should be pretty
1625 * close on average.
1626 *
1627 * Formula: suggested - needed
1628 * ----------------------------
1629 * 1 + g0_pcnt_kept/100
1630 *
1631 * where 'needed' is the amount of memory needed at the next
1632 * collection for collecting all gens except g0.
1633 */
1634 blocks =
1635 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1636 (100 + (long)g0_pcnt_kept);
1637
1638 if (blocks < (long)min_nursery) {
1639 blocks = min_nursery;
1640 }
1641
1642 resizeNurseries((nat)blocks);
1643 }
1644 else
1645 {
1646 // we might have added extra large blocks to the nursery, so
1647 // resize back to minAllocAreaSize again.
1648 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1649 }
1650 }
1651 }
1652
1653 /* -----------------------------------------------------------------------------
1654 Sanity code for CAF garbage collection.
1655
1656 With DEBUG turned on, we manage a CAF list in addition to the SRT
1657 mechanism. After GC, we run down the CAF list and blackhole any
1658 CAFs which have been garbage collected. This means we get an error
1659 whenever the program tries to enter a garbage collected CAF.
1660
1661 Any garbage collected CAFs are taken off the CAF list at the same
1662 time.
1663 -------------------------------------------------------------------------- */
1664
1665 #if 0 && defined(DEBUG)
1666
1667 static void
1668 gcCAFs(void)
1669 {
1670 StgClosure* p;
1671 StgClosure** pp;
1672 const StgInfoTable *info;
1673 nat i;
1674
1675 i = 0;
1676 p = caf_list;
1677 pp = &caf_list;
1678
1679 while (p != NULL) {
1680
1681 info = get_itbl(p);
1682
1683 ASSERT(info->type == IND_STATIC);
1684
1685 if (STATIC_LINK(info,p) == NULL) {
1686 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1687 // black hole it
1688 SET_INFO(p,&stg_BLACKHOLE_info);
1689 p = STATIC_LINK2(info,p);
1690 *pp = p;
1691 }
1692 else {
1693 pp = &STATIC_LINK2(info,p);
1694 p = *pp;
1695 i++;
1696 }
1697
1698 }
1699
1700 debugTrace(DEBUG_gccafs, "%d CAFs live", i);
1701 }
1702 #endif