summaryrefslogtreecommitdiff
path: root/allchblk.c
blob: 1a1efc6b91b920dcdacdf1582394eb63ee461443 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
/* 
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1998-1999 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1999 by Hewlett-Packard Company. All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

/* #define DEBUG */
#include <stdio.h>
#include "private/gc_priv.h"

GC_bool GC_use_entire_heap = 0;

/*
 * Free heap blocks are kept on one of several free lists,
 * depending on the size of the block.  Each free list is doubly linked.
 * Adjacent free blocks are coalesced.
 */

 
# define MAX_BLACK_LIST_ALLOC (2*HBLKSIZE)
		/* largest block we will allocate starting on a black   */
		/* listed block.  Must be >= HBLKSIZE.			*/


# define UNIQUE_THRESHOLD 32
	/* Sizes up to this many HBLKs each have their own free list    */
# define HUGE_THRESHOLD 256
	/* Sizes of at least this many heap blocks are mapped to a	*/
	/* single free list.						*/
# define FL_COMPRESSION 8
	/* In between sizes map this many distinct sizes to a single	*/
	/* bin.								*/

# define N_HBLK_FLS (HUGE_THRESHOLD - UNIQUE_THRESHOLD)/FL_COMPRESSION \
				 + UNIQUE_THRESHOLD

struct hblk * GC_hblkfreelist[N_HBLK_FLS+1] = { 0 };

#ifndef USE_MUNMAP

  word GC_free_bytes[N_HBLK_FLS+1] = { 0 };
	/* Number of free bytes on each list.	*/

  /* Is bytes + the number of free bytes on lists n .. N_HBLK_FLS 	*/
  /* > GC_max_large_allocd_bytes?					*/
# ifdef __GNUC__
  __inline__
# endif
  static GC_bool GC_enough_large_bytes_left(bytes,n)
  word bytes;
  int n;
  {
    int i;
    for (i = N_HBLK_FLS; i >= n; --i) {
	bytes += GC_free_bytes[i];
	if (bytes > GC_max_large_allocd_bytes) return TRUE;
    }
    return FALSE;
  }

# define INCR_FREE_BYTES(n, b) GC_free_bytes[n] += (b);

# define FREE_ASSERT(e) GC_ASSERT(e)

#else /* USE_MUNMAP */

# define INCR_FREE_BYTES(n, b)
# define FREE_ASSERT(e)

#endif /* USE_MUNMAP */

/* Map a number of blocks to the appropriate large block free list index. */
int GC_hblk_fl_from_blocks(blocks_needed)
word blocks_needed;
{
    if (blocks_needed <= UNIQUE_THRESHOLD) return blocks_needed;
    if (blocks_needed >= HUGE_THRESHOLD) return N_HBLK_FLS;
    return (blocks_needed - UNIQUE_THRESHOLD)/FL_COMPRESSION
					+ UNIQUE_THRESHOLD;
    
}

# define PHDR(hhdr) HDR(hhdr -> hb_prev)
# define NHDR(hhdr) HDR(hhdr -> hb_next)

# ifdef USE_MUNMAP
#   define IS_MAPPED(hhdr) (((hhdr) -> hb_flags & WAS_UNMAPPED) == 0)
# else  /* !USE_MMAP */
#   define IS_MAPPED(hhdr) 1
# endif /* USE_MUNMAP */

# if !defined(NO_DEBUGGING)
void GC_print_hblkfreelist()
{
    struct hblk * h;
    word total_free = 0;
    hdr * hhdr;
    word sz;
    int i;
    
    for (i = 0; i <= N_HBLK_FLS; ++i) {
      h = GC_hblkfreelist[i];
#     ifdef USE_MUNMAP
        if (0 != h) GC_printf1("Free list %ld:\n",
		               (unsigned long)i);
#     else
        if (0 != h) GC_printf2("Free list %ld (Total size %ld):\n",
		               (unsigned long)i,
			       (unsigned long)GC_free_bytes[i]);
#     endif
      while (h != 0) {
        hhdr = HDR(h);
        sz = hhdr -> hb_sz;
    	GC_printf2("\t0x%lx size %lu ", (unsigned long)h, (unsigned long)sz);
    	total_free += sz;
        if (GC_is_black_listed(h, HBLKSIZE) != 0) {
             GC_printf0("start black listed\n");
        } else if (GC_is_black_listed(h, hhdr -> hb_sz) != 0) {
             GC_printf0("partially black listed\n");
        } else {
             GC_printf0("not black listed\n");
        }
        h = hhdr -> hb_next;
      }
    }
#   ifndef USE_MUNMAP
      if (total_free != GC_large_free_bytes) {
	GC_printf1("GC_large_free_bytes = %lu (INCONSISTENT!!)\n",
		   (unsigned long) GC_large_free_bytes);
      }
#   endif
    GC_printf1("Total of %lu bytes on free list\n", (unsigned long)total_free);
}

/* Return the free list index on which the block described by the header */
/* appears, or -1 if it appears nowhere.				 */
int free_list_index_of(wanted)
hdr * wanted;
{
    struct hblk * h;
    hdr * hhdr;
    int i;
    
    for (i = 0; i <= N_HBLK_FLS; ++i) {
      h = GC_hblkfreelist[i];
      while (h != 0) {
        hhdr = HDR(h);
	if (hhdr == wanted) return i;
        h = hhdr -> hb_next;
      }
    }
    return -1;
}

void GC_dump_regions()
{
    unsigned i;
    ptr_t start, end;
    ptr_t p;
    size_t bytes;
    hdr *hhdr;
    for (i = 0; i < GC_n_heap_sects; ++i) {
	start = GC_heap_sects[i].hs_start;
	bytes = GC_heap_sects[i].hs_bytes;
	end = start + bytes;
	/* Merge in contiguous sections.	*/
	  while (i+1 < GC_n_heap_sects && GC_heap_sects[i+1].hs_start == end) {
	    ++i;
	    end = GC_heap_sects[i].hs_start + GC_heap_sects[i].hs_bytes;
	  }
	GC_printf2("***Section from 0x%lx to 0x%lx\n", start, end);
	for (p = start; p < end;) {
	    hhdr = HDR(p);
	    GC_printf1("\t0x%lx ", (unsigned long)p);
	    if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
		GC_printf1("Missing header!!(%ld)\n", hhdr);
		p += HBLKSIZE;
		continue;
	    }
	    if (HBLK_IS_FREE(hhdr)) {
                int correct_index = GC_hblk_fl_from_blocks(
					divHBLKSZ(hhdr -> hb_sz));
	        int actual_index;
		
		GC_printf1("\tfree block of size 0x%lx bytes",
			   (unsigned long)(hhdr -> hb_sz));
	 	if (IS_MAPPED(hhdr)) {
		    GC_printf0("\n");
		} else {
		    GC_printf0("(unmapped)\n");
		}
		actual_index = free_list_index_of(hhdr);
		if (-1 == actual_index) {
		    GC_printf1("\t\tBlock not on free list %ld!!\n",
				correct_index);
		} else if (correct_index != actual_index) {
		    GC_printf2("\t\tBlock on list %ld, should be on %ld!!\n",
			       actual_index, correct_index);
		}
		p += hhdr -> hb_sz;
	    } else {
		GC_printf1("\tused for blocks of size 0x%lx bytes\n",
			   (unsigned long)WORDS_TO_BYTES(hhdr -> hb_sz));
		p += HBLKSIZE * OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
	    }
	}
    }
}

# endif /* NO_DEBUGGING */

/* Initialize hdr for a block containing the indicated size and 	*/
/* kind of objects.							*/
/* Return FALSE on failure.						*/
static GC_bool setup_header(hhdr, sz, kind, flags)
register hdr * hhdr;
word sz;	/* object size in words */
int kind;
unsigned char flags;
{
    register word descr;
    
    /* Add description of valid object pointers */
      if (!GC_add_map_entry(sz)) return(FALSE);
      hhdr -> hb_map = GC_obj_map[sz > MAXOBJSZ? 0 : sz];
      
    /* Set size, kind and mark proc fields */
      hhdr -> hb_sz = sz;
      hhdr -> hb_obj_kind = kind;
      hhdr -> hb_flags = flags;
      descr = GC_obj_kinds[kind].ok_descriptor;
      if (GC_obj_kinds[kind].ok_relocate_descr) descr += WORDS_TO_BYTES(sz);
      hhdr -> hb_descr = descr;
      
    /* Clear mark bits */
      GC_clear_hdr_marks(hhdr);
      
    hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
    return(TRUE);
}

#define FL_UNKNOWN -1
/*
 * Remove hhdr from the appropriate free list.
 * We assume it is on the nth free list, or on the size
 * appropriate free list if n is FL_UNKNOWN.
 */
void GC_remove_from_fl(hhdr, n)
hdr * hhdr;
int n;
{
    int index;

    GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
#   ifndef USE_MUNMAP
      /* We always need index to mainatin free counts.	*/
      if (FL_UNKNOWN == n) {
          index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
      } else {
	  index = n;
      }
#   endif
    if (hhdr -> hb_prev == 0) {
#	ifdef USE_MUNMAP
	  if (FL_UNKNOWN == n) {
            index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
	  } else {
	    index = n;
	  }
#	endif
	GC_ASSERT(HDR(GC_hblkfreelist[index]) == hhdr);
	GC_hblkfreelist[index] = hhdr -> hb_next;
    } else {
	hdr *phdr;
	GET_HDR(hhdr -> hb_prev, phdr);
	phdr -> hb_next = hhdr -> hb_next;
    }
    FREE_ASSERT(GC_free_bytes[index] >= hhdr -> hb_sz);
    INCR_FREE_BYTES(index, - (signed_word)(hhdr -> hb_sz));
    if (0 != hhdr -> hb_next) {
	hdr * nhdr;
	GC_ASSERT(!IS_FORWARDING_ADDR_OR_NIL(NHDR(hhdr)));
	GET_HDR(hhdr -> hb_next, nhdr);
	nhdr -> hb_prev = hhdr -> hb_prev;
    }
}

/*
 * Return a pointer to the free block ending just before h, if any.
 */
struct hblk * GC_free_block_ending_at(h)
struct hblk *h;
{
    struct hblk * p = h - 1;
    hdr * phdr;

    GET_HDR(p, phdr);
    while (0 != phdr && IS_FORWARDING_ADDR_OR_NIL(phdr)) {
	p = FORWARDED_ADDR(p,phdr);
	phdr = HDR(p);
    }
    if (0 != phdr) {
        if(HBLK_IS_FREE(phdr)) {
	    return p;
	} else {
	    return 0;
	}
    }
    p = GC_prev_block(h - 1);
    if (0 != p) {
      phdr = HDR(p);
      if (HBLK_IS_FREE(phdr) && (ptr_t)p + phdr -> hb_sz == (ptr_t)h) {
	return p;
      }
    }
    return 0;
}

/*
 * Add hhdr to the appropriate free list.
 * We maintain individual free lists sorted by address.
 */
void GC_add_to_fl(h, hhdr)
struct hblk *h;
hdr * hhdr;
{
    int index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
    struct hblk *second = GC_hblkfreelist[index];
    hdr * second_hdr;
#   ifdef GC_ASSERTIONS
      struct hblk *next = (struct hblk *)((word)h + hhdr -> hb_sz);
      hdr * nexthdr = HDR(next);
      struct hblk *prev = GC_free_block_ending_at(h);
      hdr * prevhdr = HDR(prev);
      GC_ASSERT(nexthdr == 0 || !HBLK_IS_FREE(nexthdr) || !IS_MAPPED(nexthdr));
      GC_ASSERT(prev == 0 || !HBLK_IS_FREE(prevhdr) || !IS_MAPPED(prevhdr));
#   endif
    GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
    GC_hblkfreelist[index] = h;
    INCR_FREE_BYTES(index, hhdr -> hb_sz);
    FREE_ASSERT(GC_free_bytes[index] <= GC_large_free_bytes)
    hhdr -> hb_next = second;
    hhdr -> hb_prev = 0;
    if (0 != second) {
      GET_HDR(second, second_hdr);
      second_hdr -> hb_prev = h;
    }
    GC_invalidate_map(hhdr);
}

#ifdef USE_MUNMAP

/* Unmap blocks that haven't been recently touched.  This is the only way */
/* way blocks are ever unmapped.					  */
void GC_unmap_old(void)
{
    struct hblk * h;
    hdr * hhdr;
    word sz;
    unsigned short last_rec, threshold;
    int i;
#   define UNMAP_THRESHOLD 6
    
    for (i = 0; i <= N_HBLK_FLS; ++i) {
      for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
        hhdr = HDR(h);
	if (!IS_MAPPED(hhdr)) continue;
	threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
	last_rec = hhdr -> hb_last_reclaimed;
	if ((last_rec > GC_gc_no || last_rec < threshold)
	    && threshold < GC_gc_no /* not recently wrapped */) {
          sz = hhdr -> hb_sz;
	  GC_unmap((ptr_t)h, sz);
	  hhdr -> hb_flags |= WAS_UNMAPPED;
    	}
      }
    }  
}

/* Merge all unmapped blocks that are adjacent to other free		*/
/* blocks.  This may involve remapping, since all blocks are either	*/
/* fully mapped or fully unmapped.					*/
void GC_merge_unmapped(void)
{
    struct hblk * h, *next;
    hdr * hhdr, *nexthdr;
    word size, nextsize;
    int i;
    
    for (i = 0; i <= N_HBLK_FLS; ++i) {
      h = GC_hblkfreelist[i];
      while (h != 0) {
	GET_HDR(h, hhdr);
	size = hhdr->hb_sz;
	next = (struct hblk *)((word)h + size);
	GET_HDR(next, nexthdr);
	/* Coalesce with successor, if possible */
	  if (0 != nexthdr && HBLK_IS_FREE(nexthdr)) {
	    nextsize = nexthdr -> hb_sz;
	    if (IS_MAPPED(hhdr)) {
	      GC_ASSERT(!IS_MAPPED(nexthdr));
	      /* make both consistent, so that we can merge */
	        if (size > nextsize) {
		  GC_remap((ptr_t)next, nextsize);
		} else {
		  GC_unmap((ptr_t)h, size);
		  hhdr -> hb_flags |= WAS_UNMAPPED;
		}
	    } else if (IS_MAPPED(nexthdr)) {
	      GC_ASSERT(!IS_MAPPED(hhdr));
	      if (size > nextsize) {
		GC_unmap((ptr_t)next, nextsize);
	      } else {
		GC_remap((ptr_t)h, size);
		hhdr -> hb_flags &= ~WAS_UNMAPPED;
		hhdr -> hb_last_reclaimed = nexthdr -> hb_last_reclaimed;
	      }
	    } else {
	      /* Unmap any gap in the middle */
		GC_unmap_gap((ptr_t)h, size, (ptr_t)next, nexthdr -> hb_sz);
	    }
	    /* If they are both unmapped, we merge, but leave unmapped. */
	    GC_remove_from_fl(hhdr, i);
	    GC_remove_from_fl(nexthdr, FL_UNKNOWN);
	    hhdr -> hb_sz += nexthdr -> hb_sz; 
	    GC_remove_header(next);
	    GC_add_to_fl(h, hhdr); 
	    /* Start over at beginning of list */
	    h = GC_hblkfreelist[i];
	  } else /* not mergable with successor */ {
	    h = hhdr -> hb_next;
	  }
      } /* while (h != 0) ... */
    } /* for ... */
}

#endif /* USE_MUNMAP */

/*
 * Return a pointer to a block starting at h of length bytes.
 * Memory for the block is mapped.
 * Remove the block from its free list, and return the remainder (if any)
 * to its appropriate free list.
 * May fail by returning 0.
 * The header for the returned block must be set up by the caller.
 * If the return value is not 0, then hhdr is the header for it.
 */
struct hblk * GC_get_first_part(h, hhdr, bytes, index)
struct hblk *h;
hdr * hhdr;
word bytes;
int index;
{
    word total_size = hhdr -> hb_sz;
    struct hblk * rest;
    hdr * rest_hdr;

    GC_ASSERT((total_size & (HBLKSIZE-1)) == 0);
    GC_remove_from_fl(hhdr, index);
    if (total_size == bytes) return h;
    rest = (struct hblk *)((word)h + bytes);
    rest_hdr = GC_install_header(rest);
    if (0 == rest_hdr) {
	/* This may be very bad news ... */
	WARN("Header allocation failed: Dropping block.\n", 0);
	return(0);
    }
    rest_hdr -> hb_sz = total_size - bytes;
    rest_hdr -> hb_flags = 0;
#   ifdef GC_ASSERTIONS
      /* Mark h not free, to avoid assertion about adjacent free blocks. */
        hhdr -> hb_map = 0;
#   endif
    GC_add_to_fl(rest, rest_hdr);
    return h;
}

/*
 * H is a free block.  N points at an address inside it.
 * A new header for n has already been set up.  Fix up h's header
 * to reflect the fact that it is being split, move it to the
 * appropriate free list.
 * N replaces h in the original free list.
 *
 * Nhdr is not completely filled in, since it is about to allocated.
 * It may in fact end up on the wrong free list for its size.
 * (Hence adding it to a free list is silly.  But this path is hopefully
 * rare enough that it doesn't matter.  The code is cleaner this way.)
 */
void GC_split_block(h, hhdr, n, nhdr, index)
struct hblk *h;
hdr * hhdr;
struct hblk *n;
hdr * nhdr;
int index;	/* Index of free list */
{
    word total_size = hhdr -> hb_sz;
    word h_size = (word)n - (word)h;
    struct hblk *prev = hhdr -> hb_prev;
    struct hblk *next = hhdr -> hb_next;

    /* Replace h with n on its freelist */
      nhdr -> hb_prev = prev;
      nhdr -> hb_next = next;
      nhdr -> hb_sz = total_size - h_size;
      nhdr -> hb_flags = 0;
      if (0 != prev) {
	HDR(prev) -> hb_next = n;
      } else {
        GC_hblkfreelist[index] = n;
      }
      if (0 != next) {
	HDR(next) -> hb_prev = n;
      }
      INCR_FREE_BYTES(index, -(signed_word)h_size);
      FREE_ASSERT(GC_free_bytes[index] > 0);
#     ifdef GC_ASSERTIONS
	nhdr -> hb_map = 0;	/* Don't fail test for consecutive	*/
				/* free blocks in GC_add_to_fl.		*/
#     endif
#   ifdef USE_MUNMAP
      hhdr -> hb_last_reclaimed = GC_gc_no;
#   endif
    hhdr -> hb_sz = h_size;
    GC_add_to_fl(h, hhdr);
    GC_invalidate_map(nhdr);
}
	
struct hblk * GC_allochblk_nth();

/*
 * Allocate (and return pointer to) a heap block
 *   for objects of size sz words, searching the nth free list.
 *
 * NOTE: We set obj_map field in header correctly.
 *       Caller is responsible for building an object freelist in block.
 *
 * Unlike older versions of the collectors, the client is responsible
 * for clearing the block, if necessary.
 */
struct hblk *
GC_allochblk(sz, kind, flags)
word sz;
int kind;
unsigned flags;  /* IGNORE_OFF_PAGE or 0 */
{
    word blocks = OBJ_SZ_TO_BLOCKS(sz);
    int start_list = GC_hblk_fl_from_blocks(blocks);
    int i;
    for (i = start_list; i <= N_HBLK_FLS; ++i) {
	struct hblk * result = GC_allochblk_nth(sz, kind, flags, i);
	if (0 != result) {
	    return result;
	}
    }
    return 0;
}
/*
 * The same, but with search restricted to nth free list.
 */
struct hblk *
GC_allochblk_nth(sz, kind, flags, n)
word sz;
int kind;
unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
int n;
{
    register struct hblk *hbp;
    register hdr * hhdr;		/* Header corr. to hbp */
    register struct hblk *thishbp;
    register hdr * thishdr;		/* Header corr. to hbp */
    signed_word size_needed;    /* number of bytes in requested objects */
    signed_word size_avail;	/* bytes available in this block	*/

    size_needed = HBLKSIZE * OBJ_SZ_TO_BLOCKS(sz);

    /* search for a big enough block in free list */
	hbp = GC_hblkfreelist[n];
	for(; 0 != hbp; hbp = hhdr -> hb_next) {
	    GET_HDR(hbp, hhdr);
	    size_avail = hhdr->hb_sz;
	    if (size_avail < size_needed) continue;
	    if (size_avail != size_needed
		&& !GC_use_entire_heap
		&& !GC_dont_gc
		&& USED_HEAP_SIZE >= GC_requested_heapsize
		&& !TRUE_INCREMENTAL && GC_should_collect()) {
#		ifdef USE_MUNMAP
		    continue;
#		else
		    /* If we have enough large blocks left to cover any	*/
		    /* previous request for large blocks, we go ahead	*/
		    /* and split.  Assuming a steady state, that should	*/
		    /* be safe.  It means that we can use the full 	*/
		    /* heap if we allocate only small objects.		*/
		    if (!GC_enough_large_bytes_left(GC_large_allocd_bytes, n)) {
		      continue;
		    } 
		    /* If we are deallocating lots of memory from	*/
		    /* finalizers, fail and collect sooner rather	*/
		    /* than later.					*/
		    if (WORDS_TO_BYTES(GC_finalizer_mem_freed)
			> (GC_heapsize >> 4))  {
		      continue;
		    }
#		endif /* !USE_MUNMAP */
	    }
	    /* If the next heap block is obviously better, go on.	*/
	    /* This prevents us from disassembling a single large block */
	    /* to get tiny blocks.					*/
	    {
	      signed_word next_size;
	      
	      thishbp = hhdr -> hb_next;
	      if (thishbp != 0) {
		GET_HDR(thishbp, thishdr);
	        next_size = (signed_word)(thishdr -> hb_sz);
	        if (next_size < size_avail
	          && next_size >= size_needed
	          && !GC_is_black_listed(thishbp, (word)size_needed)) {
	          continue;
	        }
	      }
	    }
	    if ( !IS_UNCOLLECTABLE(kind) &&
	         (kind != PTRFREE || size_needed > MAX_BLACK_LIST_ALLOC)) {
	      struct hblk * lasthbp = hbp;
	      ptr_t search_end = (ptr_t)hbp + size_avail - size_needed;
	      signed_word orig_avail = size_avail;
	      signed_word eff_size_needed = ((flags & IGNORE_OFF_PAGE)?
	      					HBLKSIZE
	      					: size_needed);
	      
	      
	      while ((ptr_t)lasthbp <= search_end
	             && (thishbp = GC_is_black_listed(lasthbp,
	             				      (word)eff_size_needed))
		        != 0) {
	        lasthbp = thishbp;
	      }
	      size_avail -= (ptr_t)lasthbp - (ptr_t)hbp;
	      thishbp = lasthbp;
	      if (size_avail >= size_needed) {
	        if (thishbp != hbp &&
		    0 != (thishdr = GC_install_header(thishbp))) {
		  /* Make sure it's mapped before we mangle it. */
#		    ifdef USE_MUNMAP
		      if (!IS_MAPPED(hhdr)) {
		        GC_remap((ptr_t)hbp, hhdr -> hb_sz);
		        hhdr -> hb_flags &= ~WAS_UNMAPPED;
		      }
#		    endif
	          /* Split the block at thishbp */
		      GC_split_block(hbp, hhdr, thishbp, thishdr, n);
		  /* Advance to thishbp */
		      hbp = thishbp;
		      hhdr = thishdr;
		      /* We must now allocate thishbp, since it may	*/
		      /* be on the wrong free list.			*/
		}
	      } else if (size_needed > (signed_word)BL_LIMIT
	                 && orig_avail - size_needed
			    > (signed_word)BL_LIMIT) {
	        /* Punt, since anything else risks unreasonable heap growth. */
		if (++GC_large_alloc_warn_suppressed
		    >= GC_large_alloc_warn_interval) {
	          WARN("Repeated allocation of very large block "
		       "(appr. size %ld):\n"
		       "\tMay lead to memory leak and poor performance.\n",
		       size_needed);
		  GC_large_alloc_warn_suppressed = 0;
		}
	        size_avail = orig_avail;
	      } else if (size_avail == 0 && size_needed == HBLKSIZE
			 && IS_MAPPED(hhdr)) {
		if (!GC_find_leak) {
	      	  static unsigned count = 0;
	      	  
	      	  /* The block is completely blacklisted.  We need 	*/
	      	  /* to drop some such blocks, since otherwise we spend */
	      	  /* all our time traversing them if pointerfree	*/
	      	  /* blocks are unpopular.				*/
	          /* A dropped block will be reconsidered at next GC.	*/
	          if ((++count & 3) == 0) {
	            /* Allocate and drop the block in small chunks, to	*/
	            /* maximize the chance that we will recover some	*/
	            /* later.						*/
		      word total_size = hhdr -> hb_sz;
	              struct hblk * limit = hbp + divHBLKSZ(total_size);
	              struct hblk * h;
		      struct hblk * prev = hhdr -> hb_prev;
	              
		      GC_words_wasted += BYTES_TO_WORDS(total_size);
		      GC_large_free_bytes -= total_size;
		      GC_remove_from_fl(hhdr, n);
	              for (h = hbp; h < limit; h++) {
	                if (h == hbp || 0 != (hhdr = GC_install_header(h))) {
	                  (void) setup_header(
	                	  hhdr,
	              		  BYTES_TO_WORDS(HBLKSIZE),
	              		  PTRFREE, 0); /* Cant fail */
	              	  if (GC_debugging_started) {
	              	    BZERO(h, HBLKSIZE);
	              	  }
	                }
	              }
	            /* Restore hbp to point at free block */
		      hbp = prev;
		      if (0 == hbp) {
			return GC_allochblk_nth(sz, kind, flags, n);
		      }
	   	      hhdr = HDR(hbp);
	          }
		}
	      }
	    }
	    if( size_avail >= size_needed ) {
#		ifdef USE_MUNMAP
		  if (!IS_MAPPED(hhdr)) {
		    GC_remap((ptr_t)hbp, hhdr -> hb_sz);
		    hhdr -> hb_flags &= ~WAS_UNMAPPED;
		  }
#	        endif
		/* hbp may be on the wrong freelist; the parameter n	*/
		/* is important.					*/
		hbp = GC_get_first_part(hbp, hhdr, size_needed, n);
		break;
	    }
	}

    if (0 == hbp) return 0;
	
    /* Add it to map of valid blocks */
    	if (!GC_install_counts(hbp, (word)size_needed)) return(0);
    	/* This leaks memory under very rare conditions. */
    		
    /* Set up header */
        if (!setup_header(hhdr, sz, kind, flags)) {
            GC_remove_counts(hbp, (word)size_needed);
            return(0); /* ditto */
        }

    /* Notify virtual dirty bit implementation that we are about to write.  */
    /* Ensure that pointerfree objects are not protected if it's avoidable. */
    	GC_remove_protection(hbp, divHBLKSZ(size_needed),
			     (hhdr -> hb_descr == 0) /* pointer-free */);
        
    /* We just successfully allocated a block.  Restart count of	*/
    /* consecutive failures.						*/
    {
	extern unsigned GC_fail_count;
	
	GC_fail_count = 0;
    }

    GC_large_free_bytes -= size_needed;
    
    GC_ASSERT(IS_MAPPED(hhdr));
    return( hbp );
}
 
struct hblk * GC_freehblk_ptr = 0;  /* Search position hint for GC_freehblk */

/*
 * Free a heap block.
 *
 * Coalesce the block with its neighbors if possible.
 *
 * All mark words are assumed to be cleared.
 */
void
GC_freehblk(hbp)
struct hblk *hbp;
{
struct hblk *next, *prev;
hdr *hhdr, *prevhdr, *nexthdr;
signed_word size;


    GET_HDR(hbp, hhdr);
    size = hhdr->hb_sz;
    size = HBLKSIZE * OBJ_SZ_TO_BLOCKS(size);
    GC_remove_counts(hbp, (word)size);
    hhdr->hb_sz = size;
#   ifdef USE_MUNMAP
      hhdr -> hb_last_reclaimed = GC_gc_no;
#   endif
    
    /* Check for duplicate deallocation in the easy case */
      if (HBLK_IS_FREE(hhdr)) {
        GC_printf1("Duplicate large block deallocation of 0x%lx\n",
        	   (unsigned long) hbp);
	ABORT("Duplicate large block deallocation");
      }

    GC_ASSERT(IS_MAPPED(hhdr));
    GC_invalidate_map(hhdr);
    next = (struct hblk *)((word)hbp + size);
    GET_HDR(next, nexthdr);
    prev = GC_free_block_ending_at(hbp);
    /* Coalesce with successor, if possible */
      if(0 != nexthdr && HBLK_IS_FREE(nexthdr) && IS_MAPPED(nexthdr)) {
	GC_remove_from_fl(nexthdr, FL_UNKNOWN);
	hhdr -> hb_sz += nexthdr -> hb_sz; 
	GC_remove_header(next);
      }
    /* Coalesce with predecessor, if possible. */
      if (0 != prev) {
	prevhdr = HDR(prev);
	if (IS_MAPPED(prevhdr)) {
	  GC_remove_from_fl(prevhdr, FL_UNKNOWN);
	  prevhdr -> hb_sz += hhdr -> hb_sz;
#	  ifdef USE_MUNMAP
	    prevhdr -> hb_last_reclaimed = GC_gc_no;
#	  endif
	  GC_remove_header(hbp);
	  hbp = prev;
	  hhdr = prevhdr;
	}
      }
    /* FIXME: It is not clear we really always want to do these merges	*/
    /* with -DUSE_MUNMAP, since it updates ages and hence prevents	*/
    /* unmapping. 							*/

    GC_large_free_bytes += size;
    GC_add_to_fl(hbp, hhdr);    
}