80ec6f2019de5fabe30cd52c962904bdfa221205
[ghc.git] / rts / sm / GC.c
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 1998-2006
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 "RtsFlags.h"
17 #include "RtsUtils.h"
18 #include "Apply.h"
19 #include "OSThreads.h"
20 #include "LdvProfile.h"
21 #include "Updates.h"
22 #include "Stats.h"
23 #include "Schedule.h"
24 #include "Sanity.h"
25 #include "BlockAlloc.h"
26 #include "MBlock.h"
27 #include "ProfHeap.h"
28 #include "SchedAPI.h"
29 #include "Weak.h"
30 #include "Prelude.h"
31 #include "ParTicky.h" // ToDo: move into Rts.h
32 #include "RtsSignals.h"
33 #include "STM.h"
34 #include "HsFFI.h"
35 #include "Linker.h"
36 #if defined(RTS_GTK_FRONTPANEL)
37 #include "FrontPanel.h"
38 #endif
39 #include "Trace.h"
40 #include "RetainerProfile.h"
41 #include "RaiseAsync.h"
42 #include "Sparks.h"
43 #include "Papi.h"
44
45 #include "GC.h"
46 #include "Compact.h"
47 #include "Evac.h"
48 #include "Scav.h"
49 #include "GCUtils.h"
50 #include "MarkWeak.h"
51 #include "Sparks.h"
52
53 #include <string.h> // for memset()
54
55 /* -----------------------------------------------------------------------------
56 Global variables
57 -------------------------------------------------------------------------- */
58
59 /* STATIC OBJECT LIST.
60 *
61 * During GC:
62 * We maintain a linked list of static objects that are still live.
63 * The requirements for this list are:
64 *
65 * - we need to scan the list while adding to it, in order to
66 * scavenge all the static objects (in the same way that
67 * breadth-first scavenging works for dynamic objects).
68 *
69 * - we need to be able to tell whether an object is already on
70 * the list, to break loops.
71 *
72 * Each static object has a "static link field", which we use for
73 * linking objects on to the list. We use a stack-type list, consing
74 * objects on the front as they are added (this means that the
75 * scavenge phase is depth-first, not breadth-first, but that
76 * shouldn't matter).
77 *
78 * A separate list is kept for objects that have been scavenged
79 * already - this is so that we can zero all the marks afterwards.
80 *
81 * An object is on the list if its static link field is non-zero; this
82 * means that we have to mark the end of the list with '1', not NULL.
83 *
84 * Extra notes for generational GC:
85 *
86 * Each generation has a static object list associated with it. When
87 * collecting generations up to N, we treat the static object lists
88 * from generations > N as roots.
89 *
90 * We build up a static object list while collecting generations 0..N,
91 * which is then appended to the static object list of generation N+1.
92 */
93 StgClosure* static_objects; // live static objects
94 StgClosure* scavenged_static_objects; // static objects scavenged so far
95 #ifdef THREADED_RTS
96 SpinLock static_objects_sync;
97 #endif
98
99 /* N is the oldest generation being collected, where the generations
100 * are numbered starting at 0. A major GC (indicated by the major_gc
101 * flag) is when we're collecting all generations. We only attempt to
102 * deal with static objects and GC CAFs when doing a major GC.
103 */
104 nat N;
105 rtsBool major_gc;
106
107 /* Data used for allocation area sizing.
108 */
109 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
110
111 /* Mut-list stats */
112 #ifdef DEBUG
113 nat mutlist_MUTVARS,
114 mutlist_MUTARRS,
115 mutlist_MVARS,
116 mutlist_OTHERS;
117 #endif
118
119 /* Thread-local data for each GC thread
120 */
121 gc_thread **gc_threads = NULL;
122 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
123
124 // Number of threads running in *this* GC. Affects how many
125 // step->todos[] lists we have to look in to find work.
126 nat n_gc_threads;
127
128 // For stats:
129 long copied; // *words* copied & scavenged during this GC
130
131 #ifdef THREADED_RTS
132 SpinLock recordMutableGen_sync;
133 #endif
134
135 /* -----------------------------------------------------------------------------
136 Static function declarations
137 -------------------------------------------------------------------------- */
138
139 static void mark_root (StgClosure **root);
140 static void zero_static_object_list (StgClosure* first_static);
141 static void initialise_N (rtsBool force_major_gc);
142 static void alloc_gc_threads (void);
143 static void init_collected_gen (nat g, nat threads);
144 static void init_uncollected_gen (nat g, nat threads);
145 static void init_gc_thread (gc_thread *t);
146 static void update_task_list (void);
147 static void resize_generations (void);
148 static void resize_nursery (void);
149 static void start_gc_threads (void);
150 static void gc_thread_work (void);
151 static nat inc_running (void);
152 static nat dec_running (void);
153 static void wakeup_gc_threads (nat n_threads);
154
155 #if 0 && defined(DEBUG)
156 static void gcCAFs (void);
157 #endif
158
159 /* -----------------------------------------------------------------------------
160 The mark bitmap & stack.
161 -------------------------------------------------------------------------- */
162
163 #define MARK_STACK_BLOCKS 4
164
165 bdescr *mark_stack_bdescr;
166 StgPtr *mark_stack;
167 StgPtr *mark_sp;
168 StgPtr *mark_splim;
169
170 // Flag and pointers used for falling back to a linear scan when the
171 // mark stack overflows.
172 rtsBool mark_stack_overflowed;
173 bdescr *oldgen_scan_bd;
174 StgPtr oldgen_scan;
175
176 /* -----------------------------------------------------------------------------
177 GarbageCollect: the main entry point to the garbage collector.
178
179 Locks held: all capabilities are held throughout GarbageCollect().
180 -------------------------------------------------------------------------- */
181
182 void
183 GarbageCollect ( rtsBool force_major_gc )
184 {
185 bdescr *bd;
186 step *stp;
187 lnat live, allocated;
188 lnat oldgen_saved_blocks = 0;
189 gc_thread *saved_gct;
190 nat g, s, t;
191
192 // necessary if we stole a callee-saves register for gct:
193 saved_gct = gct;
194
195 #ifdef PROFILING
196 CostCentreStack *prev_CCS;
197 #endif
198
199 ACQUIRE_SM_LOCK;
200
201 debugTrace(DEBUG_gc, "starting GC");
202
203 #if defined(RTS_USER_SIGNALS)
204 if (RtsFlags.MiscFlags.install_signal_handlers) {
205 // block signals
206 blockUserSignals();
207 }
208 #endif
209
210 // tell the stats department that we've started a GC
211 stat_startGC();
212
213 // tell the STM to discard any cached closures it's hoping to re-use
214 stmPreGCHook();
215
216 #ifdef DEBUG
217 mutlist_MUTVARS = 0;
218 mutlist_MUTARRS = 0;
219 mutlist_OTHERS = 0;
220 #endif
221
222 // attribute any costs to CCS_GC
223 #ifdef PROFILING
224 prev_CCS = CCCS;
225 CCCS = CCS_GC;
226 #endif
227
228 /* Approximate how much we allocated.
229 * Todo: only when generating stats?
230 */
231 allocated = calcAllocated();
232
233 /* Figure out which generation to collect
234 */
235 initialise_N(force_major_gc);
236
237 /* Allocate + initialise the gc_thread structures.
238 */
239 alloc_gc_threads();
240
241 /* Start threads, so they can be spinning up while we finish initialisation.
242 */
243 start_gc_threads();
244
245 /* How many threads will be participating in this GC?
246 * We don't try to parallelise minor GC.
247 */
248 #if defined(THREADED_RTS)
249 if (N == 0) {
250 n_gc_threads = 1;
251 } else {
252 n_gc_threads = RtsFlags.ParFlags.gcThreads;
253 }
254 #else
255 n_gc_threads = 1;
256 #endif
257
258 #ifdef RTS_GTK_FRONTPANEL
259 if (RtsFlags.GcFlags.frontpanel) {
260 updateFrontPanelBeforeGC(N);
261 }
262 #endif
263
264 #ifdef DEBUG
265 // check for memory leaks if DEBUG is on
266 memInventory(traceClass(DEBUG_gc));
267 #endif
268
269 // check stack sanity *before* GC (ToDo: check all threads)
270 IF_DEBUG(sanity, checkFreeListSanity());
271
272 /* Initialise the static object lists
273 */
274 static_objects = END_OF_STATIC_LIST;
275 scavenged_static_objects = END_OF_STATIC_LIST;
276
277 // Initialise all the generations/steps that we're collecting.
278 for (g = 0; g <= N; g++) {
279 init_collected_gen(g,n_gc_threads);
280 }
281
282 // Initialise all the generations/steps that we're *not* collecting.
283 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
284 init_uncollected_gen(g,n_gc_threads);
285 }
286
287 /* Allocate a mark stack if we're doing a major collection.
288 */
289 if (major_gc) {
290 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
291 mark_stack = (StgPtr *)mark_stack_bdescr->start;
292 mark_sp = mark_stack;
293 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
294 } else {
295 mark_stack_bdescr = NULL;
296 }
297
298 // Initialise all our gc_thread structures
299 for (t = 0; t < n_gc_threads; t++) {
300 init_gc_thread(gc_threads[t]);
301 }
302
303 // the main thread is running: this prevents any other threads from
304 // exiting prematurely, so we can start them now.
305 inc_running();
306 wakeup_gc_threads(n_gc_threads);
307
308 // Initialise stats
309 copied = 0;
310
311 // this is the main thread
312 gct = gc_threads[0];
313
314 /* -----------------------------------------------------------------------
315 * follow all the roots that we know about:
316 * - mutable lists from each generation > N
317 * we want to *scavenge* these roots, not evacuate them: they're not
318 * going to move in this GC.
319 * Also do them in reverse generation order, for the usual reason:
320 * namely to reduce the likelihood of spurious old->new pointers.
321 */
322 {
323 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
324 generations[g].saved_mut_list = generations[g].mut_list;
325 generations[g].mut_list = allocBlock();
326 // mut_list always has at least one block.
327 }
328 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
329 scavenge_mutable_list(&generations[g]);
330 }
331 }
332
333 // follow roots from the CAF list (used by GHCi)
334 gct->evac_step = 0;
335 markCAFs(mark_root);
336
337 // follow all the roots that the application knows about.
338 gct->evac_step = 0;
339 GetRoots(mark_root);
340
341 #if defined(RTS_USER_SIGNALS)
342 // mark the signal handlers (signals should be already blocked)
343 markSignalHandlers(mark_root);
344 #endif
345
346 // Mark the weak pointer list, and prepare to detect dead weak pointers.
347 markWeakPtrList();
348 initWeakForGC();
349
350 // Mark the stable pointer table.
351 markStablePtrTable(mark_root);
352
353 /* -------------------------------------------------------------------------
354 * Repeatedly scavenge all the areas we know about until there's no
355 * more scavenging to be done.
356 */
357 for (;;)
358 {
359 gc_thread_work();
360 // The other threads are now stopped. We might recurse back to
361 // here, but from now on this is the only thread.
362
363 // if any blackholes are alive, make the threads that wait on
364 // them alive too.
365 if (traverseBlackholeQueue()) {
366 inc_running();
367 continue;
368 }
369
370 // must be last... invariant is that everything is fully
371 // scavenged at this point.
372 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
373 inc_running();
374 continue;
375 }
376
377 // If we get to here, there's really nothing left to do.
378 break;
379 }
380
381 // Update pointers from the Task list
382 update_task_list();
383
384 // Now see which stable names are still alive.
385 gcStablePtrTable();
386
387 #ifdef PROFILING
388 // We call processHeapClosureForDead() on every closure destroyed during
389 // the current garbage collection, so we invoke LdvCensusForDead().
390 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
391 || RtsFlags.ProfFlags.bioSelector != NULL)
392 LdvCensusForDead(N);
393 #endif
394
395 // NO MORE EVACUATION AFTER THIS POINT!
396 // Finally: compaction of the oldest generation.
397 if (major_gc && oldest_gen->steps[0].is_compacted) {
398 // save number of blocks for stats
399 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
400 compact();
401 }
402
403 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
404
405 // Two-space collector: free the old to-space.
406 // g0s0->old_blocks is the old nursery
407 // g0s0->blocks is to-space from the previous GC
408 if (RtsFlags.GcFlags.generations == 1) {
409 if (g0s0->blocks != NULL) {
410 freeChain(g0s0->blocks);
411 g0s0->blocks = NULL;
412 }
413 }
414
415 // For each workspace, in each thread:
416 // * clear the BF_EVACUATED flag from each copied block
417 // * move the copied blocks to the step
418 {
419 gc_thread *thr;
420 step_workspace *ws;
421 bdescr *prev;
422
423 for (t = 0; t < n_gc_threads; t++) {
424 thr = gc_threads[t];
425
426 // not step 0
427 for (s = 1; s < total_steps; s++) {
428 ws = &thr->steps[s];
429 // Not true?
430 // ASSERT( ws->scan_bd == ws->todo_bd );
431 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
432
433 // Push the final block
434 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
435
436 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
437
438 prev = ws->scavd_list;
439 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
440 bd->flags &= ~BF_EVACUATED; // now from-space
441 prev = bd;
442 }
443 prev->link = ws->stp->blocks;
444 ws->stp->blocks = ws->scavd_list;
445 ws->stp->n_blocks += ws->n_scavd_blocks;
446 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
447 }
448 }
449 }
450
451 // Two-space collector: swap the semi-spaces around.
452 // Currently: g0s0->old_blocks is the old nursery
453 // g0s0->blocks is to-space from this GC
454 // We want these the other way around.
455 if (RtsFlags.GcFlags.generations == 1) {
456 bdescr *nursery_blocks = g0s0->old_blocks;
457 nat n_nursery_blocks = g0s0->n_old_blocks;
458 g0s0->old_blocks = g0s0->blocks;
459 g0s0->n_old_blocks = g0s0->n_blocks;
460 g0s0->blocks = nursery_blocks;
461 g0s0->n_blocks = n_nursery_blocks;
462 }
463
464 /* run through all the generations/steps and tidy up
465 */
466 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
467
468 if (g <= N) {
469 generations[g].collections++; // for stats
470 }
471
472 // Count the mutable list as bytes "copied" for the purposes of
473 // stats. Every mutable list is copied during every GC.
474 if (g > 0) {
475 nat mut_list_size = 0;
476 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
477 mut_list_size += bd->free - bd->start;
478 }
479 copied += mut_list_size;
480
481 debugTrace(DEBUG_gc,
482 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
483 (unsigned long)(mut_list_size * sizeof(W_)),
484 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
485 }
486
487 for (s = 0; s < generations[g].n_steps; s++) {
488 bdescr *next;
489 stp = &generations[g].steps[s];
490
491 // for generations we collected...
492 if (g <= N) {
493
494 /* free old memory and shift to-space into from-space for all
495 * the collected steps (except the allocation area). These
496 * freed blocks will probaby be quickly recycled.
497 */
498 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
499 if (stp->is_compacted)
500 {
501 // for a compacted step, just shift the new to-space
502 // onto the front of the now-compacted existing blocks.
503 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
504 bd->flags &= ~BF_EVACUATED; // now from-space
505 }
506 // tack the new blocks on the end of the existing blocks
507 if (stp->old_blocks != NULL) {
508 for (bd = stp->old_blocks; bd != NULL; bd = next) {
509 // NB. this step might not be compacted next
510 // time, so reset the BF_COMPACTED flags.
511 // They are set before GC if we're going to
512 // compact. (search for BF_COMPACTED above).
513 bd->flags &= ~BF_COMPACTED;
514 next = bd->link;
515 if (next == NULL) {
516 bd->link = stp->blocks;
517 }
518 }
519 stp->blocks = stp->old_blocks;
520 }
521 // add the new blocks to the block tally
522 stp->n_blocks += stp->n_old_blocks;
523 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
524 }
525 else // not copacted
526 {
527 freeChain(stp->old_blocks);
528 }
529 stp->old_blocks = NULL;
530 stp->n_old_blocks = 0;
531 }
532
533 /* LARGE OBJECTS. The current live large objects are chained on
534 * scavenged_large, having been moved during garbage
535 * collection from large_objects. Any objects left on
536 * large_objects list are therefore dead, so we free them here.
537 */
538 for (bd = stp->large_objects; bd != NULL; bd = next) {
539 next = bd->link;
540 freeGroup(bd);
541 bd = next;
542 }
543
544 // update the count of blocks used by large objects
545 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
546 bd->flags &= ~BF_EVACUATED;
547 }
548 stp->large_objects = stp->scavenged_large_objects;
549 stp->n_large_blocks = stp->n_scavenged_large_blocks;
550
551 }
552 else // for older generations...
553 {
554 /* For older generations, we need to append the
555 * scavenged_large_object list (i.e. large objects that have been
556 * promoted during this GC) to the large_object list for that step.
557 */
558 for (bd = stp->scavenged_large_objects; bd; bd = next) {
559 next = bd->link;
560 bd->flags &= ~BF_EVACUATED;
561 dbl_link_onto(bd, &stp->large_objects);
562 }
563
564 // add the new blocks we promoted during this GC
565 stp->n_large_blocks += stp->n_scavenged_large_blocks;
566 }
567 }
568 }
569
570 // update the max size of older generations after a major GC
571 resize_generations();
572
573 // Guess the amount of live data for stats.
574 live = calcLiveBlocks() * BLOCK_SIZE_W;
575 debugTrace(DEBUG_gc, "Slop: %ldKB",
576 (live - calcLiveWords()) / (1024/sizeof(W_)));
577
578 // Free the small objects allocated via allocate(), since this will
579 // all have been copied into G0S1 now.
580 if (RtsFlags.GcFlags.generations > 1) {
581 if (g0s0->blocks != NULL) {
582 freeChain(g0s0->blocks);
583 g0s0->blocks = NULL;
584 }
585 g0s0->n_blocks = 0;
586 }
587 alloc_blocks = 0;
588 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
589
590 // Start a new pinned_object_block
591 pinned_object_block = NULL;
592
593 // Free the mark stack.
594 if (mark_stack_bdescr != NULL) {
595 freeGroup(mark_stack_bdescr);
596 }
597
598 // Free any bitmaps.
599 for (g = 0; g <= N; g++) {
600 for (s = 0; s < generations[g].n_steps; s++) {
601 stp = &generations[g].steps[s];
602 if (stp->bitmap != NULL) {
603 freeGroup(stp->bitmap);
604 stp->bitmap = NULL;
605 }
606 }
607 }
608
609 resize_nursery();
610
611 // mark the garbage collected CAFs as dead
612 #if 0 && defined(DEBUG) // doesn't work at the moment
613 if (major_gc) { gcCAFs(); }
614 #endif
615
616 #ifdef PROFILING
617 // resetStaticObjectForRetainerProfiling() must be called before
618 // zeroing below.
619 resetStaticObjectForRetainerProfiling();
620 #endif
621
622 // zero the scavenged static object list
623 if (major_gc) {
624 zero_static_object_list(scavenged_static_objects);
625 }
626
627 // Reset the nursery
628 resetNurseries();
629
630 // start any pending finalizers
631 RELEASE_SM_LOCK;
632 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
633 ACQUIRE_SM_LOCK;
634
635 // send exceptions to any threads which were about to die
636 RELEASE_SM_LOCK;
637 resurrectThreads(resurrected_threads);
638 ACQUIRE_SM_LOCK;
639
640 // Update the stable pointer hash table.
641 updateStablePtrTable(major_gc);
642
643 // check sanity after GC
644 IF_DEBUG(sanity, checkSanity());
645
646 // extra GC trace info
647 IF_DEBUG(gc, statDescribeGens());
648
649 #ifdef DEBUG
650 // symbol-table based profiling
651 /* heapCensus(to_blocks); */ /* ToDo */
652 #endif
653
654 // restore enclosing cost centre
655 #ifdef PROFILING
656 CCCS = prev_CCS;
657 #endif
658
659 #ifdef DEBUG
660 // check for memory leaks if DEBUG is on
661 memInventory(traceClass(DEBUG_gc));
662 #endif
663
664 #ifdef RTS_GTK_FRONTPANEL
665 if (RtsFlags.GcFlags.frontpanel) {
666 updateFrontPanelAfterGC( N, live );
667 }
668 #endif
669
670 // ok, GC over: tell the stats department what happened.
671 stat_endGC(allocated, live, copied, N);
672
673 #if defined(RTS_USER_SIGNALS)
674 if (RtsFlags.MiscFlags.install_signal_handlers) {
675 // unblock signals again
676 unblockUserSignals();
677 }
678 #endif
679
680 RELEASE_SM_LOCK;
681
682 gct = saved_gct;
683 }
684
685 /* -----------------------------------------------------------------------------
686 * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
687 * implicit slide i.e. after marking all sparks are at the beginning of the
688 * spark pool and the spark pool only contains sparkable closures
689 * -------------------------------------------------------------------------- */
690
691 #ifdef THREADED_RTS
692 static void
693 markSparkQueue (evac_fn evac, Capability *cap)
694 {
695 StgClosure **sparkp, **to_sparkp;
696 nat n, pruned_sparks; // stats only
697 StgSparkPool *pool;
698
699 PAR_TICKY_MARK_SPARK_QUEUE_START();
700
701 n = 0;
702 pruned_sparks = 0;
703
704 pool = &(cap->r.rSparks);
705
706 ASSERT_SPARK_POOL_INVARIANTS(pool);
707
708 #if defined(PARALLEL_HASKELL)
709 // stats only
710 n = 0;
711 pruned_sparks = 0;
712 #endif
713
714 sparkp = pool->hd;
715 to_sparkp = pool->hd;
716 while (sparkp != pool->tl) {
717 ASSERT(*sparkp!=NULL);
718 ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
719 // ToDo?: statistics gathering here (also for GUM!)
720 if (closure_SHOULD_SPARK(*sparkp)) {
721 evac(sparkp);
722 *to_sparkp++ = *sparkp;
723 if (to_sparkp == pool->lim) {
724 to_sparkp = pool->base;
725 }
726 n++;
727 } else {
728 pruned_sparks++;
729 }
730 sparkp++;
731 if (sparkp == pool->lim) {
732 sparkp = pool->base;
733 }
734 }
735 pool->tl = to_sparkp;
736
737 PAR_TICKY_MARK_SPARK_QUEUE_END(n);
738
739 #if defined(PARALLEL_HASKELL)
740 debugTrace(DEBUG_sched,
741 "marked %d sparks and pruned %d sparks on [%x]",
742 n, pruned_sparks, mytid);
743 #else
744 debugTrace(DEBUG_sched,
745 "marked %d sparks and pruned %d sparks",
746 n, pruned_sparks);
747 #endif
748
749 debugTrace(DEBUG_sched,
750 "new spark queue len=%d; (hd=%p; tl=%p)\n",
751 sparkPoolSize(pool), pool->hd, pool->tl);
752 }
753 #endif
754
755 /* ---------------------------------------------------------------------------
756 Where are the roots that we know about?
757
758 - all the threads on the runnable queue
759 - all the threads on the blocked queue
760 - all the threads on the sleeping queue
761 - all the thread currently executing a _ccall_GC
762 - all the "main threads"
763
764 ------------------------------------------------------------------------ */
765
766 void
767 GetRoots( evac_fn evac )
768 {
769 nat i;
770 Capability *cap;
771 Task *task;
772
773 // Each GC thread is responsible for following roots from the
774 // Capability of the same number. There will usually be the same
775 // or fewer Capabilities as GC threads, but just in case there
776 // are more, we mark every Capability whose number is the GC
777 // thread's index plus a multiple of the number of GC threads.
778 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
779 cap = &capabilities[i];
780 evac((StgClosure **)(void *)&cap->run_queue_hd);
781 evac((StgClosure **)(void *)&cap->run_queue_tl);
782 #if defined(THREADED_RTS)
783 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
784 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
785 #endif
786 for (task = cap->suspended_ccalling_tasks; task != NULL;
787 task=task->next) {
788 debugTrace(DEBUG_sched,
789 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
790 evac((StgClosure **)(void *)&task->suspended_tso);
791 }
792
793 #if defined(THREADED_RTS)
794 markSparkQueue(evac,cap);
795 #endif
796 }
797
798 #if !defined(THREADED_RTS)
799 evac((StgClosure **)(void *)&blocked_queue_hd);
800 evac((StgClosure **)(void *)&blocked_queue_tl);
801 evac((StgClosure **)(void *)&sleeping_queue);
802 #endif
803 }
804
805 /* -----------------------------------------------------------------------------
806 isAlive determines whether the given closure is still alive (after
807 a garbage collection) or not. It returns the new address of the
808 closure if it is alive, or NULL otherwise.
809
810 NOTE: Use it before compaction only!
811 It untags and (if needed) retags pointers to closures.
812 -------------------------------------------------------------------------- */
813
814
815 StgClosure *
816 isAlive(StgClosure *p)
817 {
818 const StgInfoTable *info;
819 bdescr *bd;
820 StgWord tag;
821 StgClosure *q;
822
823 while (1) {
824 /* The tag and the pointer are split, to be merged later when needed. */
825 tag = GET_CLOSURE_TAG(p);
826 q = UNTAG_CLOSURE(p);
827
828 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
829 info = get_itbl(q);
830
831 // ignore static closures
832 //
833 // ToDo: for static closures, check the static link field.
834 // Problem here is that we sometimes don't set the link field, eg.
835 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
836 //
837 if (!HEAP_ALLOCED(q)) {
838 return p;
839 }
840
841 // ignore closures in generations that we're not collecting.
842 bd = Bdescr((P_)q);
843 if (bd->gen_no > N) {
844 return p;
845 }
846
847 // if it's a pointer into to-space, then we're done
848 if (bd->flags & BF_EVACUATED) {
849 return p;
850 }
851
852 // large objects use the evacuated flag
853 if (bd->flags & BF_LARGE) {
854 return NULL;
855 }
856
857 // check the mark bit for compacted steps
858 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
859 return p;
860 }
861
862 switch (info->type) {
863
864 case IND:
865 case IND_STATIC:
866 case IND_PERM:
867 case IND_OLDGEN: // rely on compatible layout with StgInd
868 case IND_OLDGEN_PERM:
869 // follow indirections
870 p = ((StgInd *)q)->indirectee;
871 continue;
872
873 case EVACUATED:
874 // alive!
875 return ((StgEvacuated *)q)->evacuee;
876
877 case TSO:
878 if (((StgTSO *)q)->what_next == ThreadRelocated) {
879 p = (StgClosure *)((StgTSO *)q)->link;
880 continue;
881 }
882 return NULL;
883
884 default:
885 // dead.
886 return NULL;
887 }
888 }
889 }
890
891 /* -----------------------------------------------------------------------------
892 Figure out which generation to collect, initialise N and major_gc.
893 -------------------------------------------------------------------------- */
894
895 static void
896 initialise_N (rtsBool force_major_gc)
897 {
898 nat g;
899
900 if (force_major_gc) {
901 N = RtsFlags.GcFlags.generations - 1;
902 major_gc = rtsTrue;
903 } else {
904 N = 0;
905 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
906 if (generations[g].steps[0].n_blocks +
907 generations[g].steps[0].n_large_blocks
908 >= generations[g].max_blocks) {
909 N = g;
910 }
911 }
912 major_gc = (N == RtsFlags.GcFlags.generations-1);
913 }
914 }
915
916 /* -----------------------------------------------------------------------------
917 Initialise the gc_thread structures.
918 -------------------------------------------------------------------------- */
919
920 static gc_thread *
921 alloc_gc_thread (int n)
922 {
923 nat s;
924 step_workspace *ws;
925 gc_thread *t;
926
927 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
928 "alloc_gc_thread");
929
930 #ifdef THREADED_RTS
931 t->id = 0;
932 initCondition(&t->wake_cond);
933 initMutex(&t->wake_mutex);
934 t->wakeup = rtsFalse;
935 t->exit = rtsFalse;
936 #endif
937
938 t->thread_index = n;
939 t->free_blocks = NULL;
940 t->gc_count = 0;
941
942 init_gc_thread(t);
943
944 #ifdef USE_PAPI
945 t->papi_events = -1;
946 #endif
947
948 for (s = 0; s < total_steps; s++)
949 {
950 ws = &t->steps[s];
951 ws->stp = &all_steps[s];
952 ASSERT(s == ws->stp->abs_no);
953 ws->gct = t;
954
955 ws->scan_bd = NULL;
956 ws->scan = NULL;
957
958 ws->todo_bd = NULL;
959 ws->buffer_todo_bd = NULL;
960
961 ws->scavd_list = NULL;
962 ws->n_scavd_blocks = 0;
963 }
964
965 return t;
966 }
967
968
969 static void
970 alloc_gc_threads (void)
971 {
972 if (gc_threads == NULL) {
973 #if defined(THREADED_RTS)
974 nat i;
975 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
976 sizeof(gc_thread*),
977 "alloc_gc_threads");
978
979 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
980 gc_threads[i] = alloc_gc_thread(i);
981 }
982 #else
983 gc_threads = stgMallocBytes (sizeof(gc_thread*),
984 "alloc_gc_threads");
985
986 gc_threads[0] = alloc_gc_thread(0);
987 #endif
988 }
989 }
990
991 /* ----------------------------------------------------------------------------
992 Start GC threads
993 ------------------------------------------------------------------------- */
994
995 static nat gc_running_threads;
996
997 #if defined(THREADED_RTS)
998 static Mutex gc_running_mutex;
999 #endif
1000
1001 static nat
1002 inc_running (void)
1003 {
1004 nat n_running;
1005 ACQUIRE_LOCK(&gc_running_mutex);
1006 n_running = ++gc_running_threads;
1007 RELEASE_LOCK(&gc_running_mutex);
1008 return n_running;
1009 }
1010
1011 static nat
1012 dec_running (void)
1013 {
1014 nat n_running;
1015 ACQUIRE_LOCK(&gc_running_mutex);
1016 n_running = --gc_running_threads;
1017 RELEASE_LOCK(&gc_running_mutex);
1018 return n_running;
1019 }
1020
1021 //
1022 // gc_thread_work(): Scavenge until there's no work left to do and all
1023 // the running threads are idle.
1024 //
1025 static void
1026 gc_thread_work (void)
1027 {
1028 nat r;
1029
1030 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1031
1032 // gc_running_threads has already been incremented for us; either
1033 // this is the main thread and we incremented it inside
1034 // GarbageCollect(), or this is a worker thread and the main
1035 // thread bumped gc_running_threads before waking us up.
1036
1037 // Every thread evacuates some roots.
1038 gct->evac_step = 0;
1039 GetRoots(mark_root);
1040
1041 loop:
1042 scavenge_loop();
1043 // scavenge_loop() only exits when there's no work to do
1044 r = dec_running();
1045
1046 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1047 gct->thread_index, r);
1048
1049 while (gc_running_threads != 0) {
1050 if (any_work()) {
1051 inc_running();
1052 goto loop;
1053 }
1054 // any_work() does not remove the work from the queue, it
1055 // just checks for the presence of work. If we find any,
1056 // then we increment gc_running_threads and go back to
1057 // scavenge_loop() to perform any pending work.
1058 }
1059
1060 // All threads are now stopped
1061 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1062 }
1063
1064
1065 #if defined(THREADED_RTS)
1066 static void
1067 gc_thread_mainloop (void)
1068 {
1069 while (!gct->exit) {
1070
1071 // Wait until we're told to wake up
1072 ACQUIRE_LOCK(&gct->wake_mutex);
1073 while (!gct->wakeup) {
1074 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1075 gct->thread_index);
1076 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1077 }
1078 RELEASE_LOCK(&gct->wake_mutex);
1079 gct->wakeup = rtsFalse;
1080 if (gct->exit) break;
1081
1082 #ifdef USE_PAPI
1083 // start performance counters in this thread...
1084 if (gct->papi_events == -1) {
1085 papi_init_eventset(&gct->papi_events);
1086 }
1087 papi_thread_start_gc1_count(gct->papi_events);
1088 #endif
1089
1090 gc_thread_work();
1091
1092 #ifdef USE_PAPI
1093 // count events in this thread towards the GC totals
1094 papi_thread_stop_gc1_count(gct->papi_events);
1095 #endif
1096 }
1097 }
1098 #endif
1099
1100 #if defined(THREADED_RTS)
1101 static void
1102 gc_thread_entry (gc_thread *my_gct)
1103 {
1104 gct = my_gct;
1105 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1106 gct->id = osThreadId();
1107 gc_thread_mainloop();
1108 }
1109 #endif
1110
1111 static void
1112 start_gc_threads (void)
1113 {
1114 #if defined(THREADED_RTS)
1115 nat i;
1116 OSThreadId id;
1117 static rtsBool done = rtsFalse;
1118
1119 gc_running_threads = 0;
1120 initMutex(&gc_running_mutex);
1121
1122 if (!done) {
1123 // Start from 1: the main thread is 0
1124 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1125 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1126 gc_threads[i]);
1127 }
1128 done = rtsTrue;
1129 }
1130 #endif
1131 }
1132
1133 static void
1134 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1135 {
1136 #if defined(THREADED_RTS)
1137 nat i;
1138 for (i=1; i < n_threads; i++) {
1139 inc_running();
1140 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1141 gc_threads[i]->wakeup = rtsTrue;
1142 signalCondition(&gc_threads[i]->wake_cond);
1143 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1144 }
1145 #endif
1146 }
1147
1148 /* ----------------------------------------------------------------------------
1149 Initialise a generation that is to be collected
1150 ------------------------------------------------------------------------- */
1151
1152 static void
1153 init_collected_gen (nat g, nat n_threads)
1154 {
1155 nat s, t, i;
1156 step_workspace *ws;
1157 step *stp;
1158 bdescr *bd;
1159
1160 // Throw away the current mutable list. Invariant: the mutable
1161 // list always has at least one block; this means we can avoid a
1162 // check for NULL in recordMutable().
1163 if (g != 0) {
1164 freeChain(generations[g].mut_list);
1165 generations[g].mut_list = allocBlock();
1166 for (i = 0; i < n_capabilities; i++) {
1167 freeChain(capabilities[i].mut_lists[g]);
1168 capabilities[i].mut_lists[g] = allocBlock();
1169 }
1170 }
1171
1172 for (s = 0; s < generations[g].n_steps; s++) {
1173
1174 // generation 0, step 0 doesn't need to-space
1175 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1176 continue;
1177 }
1178
1179 stp = &generations[g].steps[s];
1180 ASSERT(stp->gen_no == g);
1181
1182 // deprecate the existing blocks
1183 stp->old_blocks = stp->blocks;
1184 stp->n_old_blocks = stp->n_blocks;
1185 stp->blocks = NULL;
1186 stp->n_blocks = 0;
1187
1188 // we don't have any to-be-scavenged blocks yet
1189 stp->todos = NULL;
1190 stp->n_todos = 0;
1191
1192 // initialise the large object queues.
1193 stp->scavenged_large_objects = NULL;
1194 stp->n_scavenged_large_blocks = 0;
1195
1196 // mark the large objects as not evacuated yet
1197 for (bd = stp->large_objects; bd; bd = bd->link) {
1198 bd->flags &= ~BF_EVACUATED;
1199 }
1200
1201 // for a compacted step, we need to allocate the bitmap
1202 if (stp->is_compacted) {
1203 nat bitmap_size; // in bytes
1204 bdescr *bitmap_bdescr;
1205 StgWord *bitmap;
1206
1207 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1208
1209 if (bitmap_size > 0) {
1210 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1211 / BLOCK_SIZE);
1212 stp->bitmap = bitmap_bdescr;
1213 bitmap = bitmap_bdescr->start;
1214
1215 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1216 bitmap_size, bitmap);
1217
1218 // don't forget to fill it with zeros!
1219 memset(bitmap, 0, bitmap_size);
1220
1221 // For each block in this step, point to its bitmap from the
1222 // block descriptor.
1223 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1224 bd->u.bitmap = bitmap;
1225 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1226
1227 // Also at this point we set the BF_COMPACTED flag
1228 // for this block. The invariant is that
1229 // BF_COMPACTED is always unset, except during GC
1230 // when it is set on those blocks which will be
1231 // compacted.
1232 bd->flags |= BF_COMPACTED;
1233 }
1234 }
1235 }
1236 }
1237
1238 // For each GC thread, for each step, allocate a "todo" block to
1239 // store evacuated objects to be scavenged, and a block to store
1240 // evacuated objects that do not need to be scavenged.
1241 for (t = 0; t < n_threads; t++) {
1242 for (s = 0; s < generations[g].n_steps; s++) {
1243
1244 // we don't copy objects into g0s0, unless -G0
1245 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1246
1247 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1248
1249 ws->scan_bd = NULL;
1250 ws->scan = NULL;
1251
1252 ws->todo_large_objects = NULL;
1253
1254 // allocate the first to-space block; extra blocks will be
1255 // chained on as necessary.
1256 ws->todo_bd = NULL;
1257 ws->buffer_todo_bd = NULL;
1258 gc_alloc_todo_block(ws);
1259
1260 ws->scavd_list = NULL;
1261 ws->n_scavd_blocks = 0;
1262 }
1263 }
1264 }
1265
1266
1267 /* ----------------------------------------------------------------------------
1268 Initialise a generation that is *not* to be collected
1269 ------------------------------------------------------------------------- */
1270
1271 static void
1272 init_uncollected_gen (nat g, nat threads)
1273 {
1274 nat s, t, i;
1275 step_workspace *ws;
1276 step *stp;
1277 bdescr *bd;
1278
1279 for (s = 0; s < generations[g].n_steps; s++) {
1280 stp = &generations[g].steps[s];
1281 stp->scavenged_large_objects = NULL;
1282 stp->n_scavenged_large_blocks = 0;
1283 }
1284
1285 for (t = 0; t < threads; t++) {
1286 for (s = 0; s < generations[g].n_steps; s++) {
1287
1288 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1289 stp = ws->stp;
1290
1291 ws->buffer_todo_bd = NULL;
1292 ws->todo_large_objects = NULL;
1293
1294 ws->scavd_list = NULL;
1295 ws->n_scavd_blocks = 0;
1296
1297 // If the block at the head of the list in this generation
1298 // is less than 3/4 full, then use it as a todo block.
1299 if (stp->blocks && isPartiallyFull(stp->blocks))
1300 {
1301 ws->todo_bd = stp->blocks;
1302 ws->todo_free = ws->todo_bd->free;
1303 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1304 stp->blocks = stp->blocks->link;
1305 stp->n_blocks -= 1;
1306 ws->todo_bd->link = NULL;
1307
1308 // this block is also the scan block; we must scan
1309 // from the current end point.
1310 ws->scan_bd = ws->todo_bd;
1311 ws->scan = ws->scan_bd->free;
1312
1313 // subtract the contents of this block from the stats,
1314 // because we'll count the whole block later.
1315 copied -= ws->scan_bd->free - ws->scan_bd->start;
1316 }
1317 else
1318 {
1319 ws->scan_bd = NULL;
1320 ws->scan = NULL;
1321 ws->todo_bd = NULL;
1322 gc_alloc_todo_block(ws);
1323 }
1324 }
1325 }
1326
1327 // Move the private mutable lists from each capability onto the
1328 // main mutable list for the generation.
1329 for (i = 0; i < n_capabilities; i++) {
1330 for (bd = capabilities[i].mut_lists[g];
1331 bd->link != NULL; bd = bd->link) {
1332 /* nothing */
1333 }
1334 bd->link = generations[g].mut_list;
1335 generations[g].mut_list = capabilities[i].mut_lists[g];
1336 capabilities[i].mut_lists[g] = allocBlock();
1337 }
1338 }
1339
1340 /* -----------------------------------------------------------------------------
1341 Initialise a gc_thread before GC
1342 -------------------------------------------------------------------------- */
1343
1344 static void
1345 init_gc_thread (gc_thread *t)
1346 {
1347 t->evac_step = 0;
1348 t->failed_to_evac = rtsFalse;
1349 t->eager_promotion = rtsTrue;
1350 t->thunk_selector_depth = 0;
1351 }
1352
1353 /* -----------------------------------------------------------------------------
1354 Function we pass to GetRoots to evacuate roots.
1355 -------------------------------------------------------------------------- */
1356
1357 static void
1358 mark_root(StgClosure **root)
1359 {
1360 evacuate(root);
1361 }
1362
1363 /* -----------------------------------------------------------------------------
1364 Initialising the static object & mutable lists
1365 -------------------------------------------------------------------------- */
1366
1367 static void
1368 zero_static_object_list(StgClosure* first_static)
1369 {
1370 StgClosure* p;
1371 StgClosure* link;
1372 const StgInfoTable *info;
1373
1374 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1375 info = get_itbl(p);
1376 link = *STATIC_LINK(info, p);
1377 *STATIC_LINK(info,p) = NULL;
1378 }
1379 }
1380
1381 /* -----------------------------------------------------------------------------
1382 Reverting CAFs
1383 -------------------------------------------------------------------------- */
1384
1385 void
1386 revertCAFs( void )
1387 {
1388 StgIndStatic *c;
1389
1390 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1391 c = (StgIndStatic *)c->static_link)
1392 {
1393 SET_INFO(c, c->saved_info);
1394 c->saved_info = NULL;
1395 // could, but not necessary: c->static_link = NULL;
1396 }
1397 revertible_caf_list = NULL;
1398 }
1399
1400 void
1401 markCAFs( evac_fn evac )
1402 {
1403 StgIndStatic *c;
1404
1405 for (c = (StgIndStatic *)caf_list; c != NULL;
1406 c = (StgIndStatic *)c->static_link)
1407 {
1408 evac(&c->indirectee);
1409 }
1410 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1411 c = (StgIndStatic *)c->static_link)
1412 {
1413 evac(&c->indirectee);
1414 }
1415 }
1416
1417 /* ----------------------------------------------------------------------------
1418 Update the pointers from the task list
1419
1420 These are treated as weak pointers because we want to allow a main
1421 thread to get a BlockedOnDeadMVar exception in the same way as any
1422 other thread. Note that the threads should all have been retained
1423 by GC by virtue of being on the all_threads list, we're just
1424 updating pointers here.
1425 ------------------------------------------------------------------------- */
1426
1427 static void
1428 update_task_list (void)
1429 {
1430 Task *task;
1431 StgTSO *tso;
1432 for (task = all_tasks; task != NULL; task = task->all_link) {
1433 if (!task->stopped && task->tso) {
1434 ASSERT(task->tso->bound == task);
1435 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1436 if (tso == NULL) {
1437 barf("task %p: main thread %d has been GC'd",
1438 #ifdef THREADED_RTS
1439 (void *)task->id,
1440 #else
1441 (void *)task,
1442 #endif
1443 task->tso->id);
1444 }
1445 task->tso = tso;
1446 }
1447 }
1448 }
1449
1450 /* ----------------------------------------------------------------------------
1451 Reset the sizes of the older generations when we do a major
1452 collection.
1453
1454 CURRENT STRATEGY: make all generations except zero the same size.
1455 We have to stay within the maximum heap size, and leave a certain
1456 percentage of the maximum heap size available to allocate into.
1457 ------------------------------------------------------------------------- */
1458
1459 static void
1460 resize_generations (void)
1461 {
1462 nat g;
1463
1464 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1465 nat live, size, min_alloc;
1466 nat max = RtsFlags.GcFlags.maxHeapSize;
1467 nat gens = RtsFlags.GcFlags.generations;
1468
1469 // live in the oldest generations
1470 live = oldest_gen->steps[0].n_blocks +
1471 oldest_gen->steps[0].n_large_blocks;
1472
1473 // default max size for all generations except zero
1474 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1475 RtsFlags.GcFlags.minOldGenSize);
1476
1477 // minimum size for generation zero
1478 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1479 RtsFlags.GcFlags.minAllocAreaSize);
1480
1481 // Auto-enable compaction when the residency reaches a
1482 // certain percentage of the maximum heap size (default: 30%).
1483 if (RtsFlags.GcFlags.generations > 1 &&
1484 (RtsFlags.GcFlags.compact ||
1485 (max > 0 &&
1486 oldest_gen->steps[0].n_blocks >
1487 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1488 oldest_gen->steps[0].is_compacted = 1;
1489 // debugBelch("compaction: on\n", live);
1490 } else {
1491 oldest_gen->steps[0].is_compacted = 0;
1492 // debugBelch("compaction: off\n", live);
1493 }
1494
1495 // if we're going to go over the maximum heap size, reduce the
1496 // size of the generations accordingly. The calculation is
1497 // different if compaction is turned on, because we don't need
1498 // to double the space required to collect the old generation.
1499 if (max != 0) {
1500
1501 // this test is necessary to ensure that the calculations
1502 // below don't have any negative results - we're working
1503 // with unsigned values here.
1504 if (max < min_alloc) {
1505 heapOverflow();
1506 }
1507
1508 if (oldest_gen->steps[0].is_compacted) {
1509 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1510 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1511 }
1512 } else {
1513 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1514 size = (max - min_alloc) / ((gens - 1) * 2);
1515 }
1516 }
1517
1518 if (size < live) {
1519 heapOverflow();
1520 }
1521 }
1522
1523 #if 0
1524 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1525 min_alloc, size, max);
1526 #endif
1527
1528 for (g = 0; g < gens; g++) {
1529 generations[g].max_blocks = size;
1530 }
1531 }
1532 }
1533
1534 /* -----------------------------------------------------------------------------
1535 Calculate the new size of the nursery, and resize it.
1536 -------------------------------------------------------------------------- */
1537
1538 static void
1539 resize_nursery (void)
1540 {
1541 if (RtsFlags.GcFlags.generations == 1)
1542 { // Two-space collector:
1543 nat blocks;
1544
1545 /* set up a new nursery. Allocate a nursery size based on a
1546 * function of the amount of live data (by default a factor of 2)
1547 * Use the blocks from the old nursery if possible, freeing up any
1548 * left over blocks.
1549 *
1550 * If we get near the maximum heap size, then adjust our nursery
1551 * size accordingly. If the nursery is the same size as the live
1552 * data (L), then we need 3L bytes. We can reduce the size of the
1553 * nursery to bring the required memory down near 2L bytes.
1554 *
1555 * A normal 2-space collector would need 4L bytes to give the same
1556 * performance we get from 3L bytes, reducing to the same
1557 * performance at 2L bytes.
1558 */
1559 blocks = g0s0->n_old_blocks;
1560
1561 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1562 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1563 RtsFlags.GcFlags.maxHeapSize )
1564 {
1565 long adjusted_blocks; // signed on purpose
1566 int pc_free;
1567
1568 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1569
1570 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1571 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1572
1573 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1574 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1575 {
1576 heapOverflow();
1577 }
1578 blocks = adjusted_blocks;
1579 }
1580 else
1581 {
1582 blocks *= RtsFlags.GcFlags.oldGenFactor;
1583 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1584 {
1585 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1586 }
1587 }
1588 resizeNurseries(blocks);
1589 }
1590 else // Generational collector
1591 {
1592 /*
1593 * If the user has given us a suggested heap size, adjust our
1594 * allocation area to make best use of the memory available.
1595 */
1596 if (RtsFlags.GcFlags.heapSizeSuggestion)
1597 {
1598 long blocks;
1599 nat needed = calcNeeded(); // approx blocks needed at next GC
1600
1601 /* Guess how much will be live in generation 0 step 0 next time.
1602 * A good approximation is obtained by finding the
1603 * percentage of g0s0 that was live at the last minor GC.
1604 *
1605 * We have an accurate figure for the amount of copied data in
1606 * 'copied', but we must convert this to a number of blocks, with
1607 * a small adjustment for estimated slop at the end of a block
1608 * (- 10 words).
1609 */
1610 if (N == 0)
1611 {
1612 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1613 / countNurseryBlocks();
1614 }
1615
1616 /* Estimate a size for the allocation area based on the
1617 * information available. We might end up going slightly under
1618 * or over the suggested heap size, but we should be pretty
1619 * close on average.
1620 *
1621 * Formula: suggested - needed
1622 * ----------------------------
1623 * 1 + g0s0_pcnt_kept/100
1624 *
1625 * where 'needed' is the amount of memory needed at the next
1626 * collection for collecting all steps except g0s0.
1627 */
1628 blocks =
1629 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1630 (100 + (long)g0s0_pcnt_kept);
1631
1632 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1633 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1634 }
1635
1636 resizeNurseries((nat)blocks);
1637 }
1638 else
1639 {
1640 // we might have added extra large blocks to the nursery, so
1641 // resize back to minAllocAreaSize again.
1642 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1643 }
1644 }
1645 }
1646
1647 /* -----------------------------------------------------------------------------
1648 Sanity code for CAF garbage collection.
1649
1650 With DEBUG turned on, we manage a CAF list in addition to the SRT
1651 mechanism. After GC, we run down the CAF list and blackhole any
1652 CAFs which have been garbage collected. This means we get an error
1653 whenever the program tries to enter a garbage collected CAF.
1654
1655 Any garbage collected CAFs are taken off the CAF list at the same
1656 time.
1657 -------------------------------------------------------------------------- */
1658
1659 #if 0 && defined(DEBUG)
1660
1661 static void
1662 gcCAFs(void)
1663 {
1664 StgClosure* p;
1665 StgClosure** pp;
1666 const StgInfoTable *info;
1667 nat i;
1668
1669 i = 0;
1670 p = caf_list;
1671 pp = &caf_list;
1672
1673 while (p != NULL) {
1674
1675 info = get_itbl(p);
1676
1677 ASSERT(info->type == IND_STATIC);
1678
1679 if (STATIC_LINK(info,p) == NULL) {
1680 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1681 // black hole it
1682 SET_INFO(p,&stg_BLACKHOLE_info);
1683 p = STATIC_LINK2(info,p);
1684 *pp = p;
1685 }
1686 else {
1687 pp = &STATIC_LINK2(info,p);
1688 p = *pp;
1689 i++;
1690 }
1691
1692 }
1693
1694 debugTrace(DEBUG_gccafs, "%d CAFs live", i);
1695 }
1696 #endif