libgc/allchblk.c

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   4  * Copyright (c) 1998-1999 by Silicon Graphics.  All rights reserved.
   5  * Copyright (c) 1999 by Hewlett-Packard Company. All rights reserved.
   6  *
   7  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   8  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   9  *
  10  * Permission is hereby granted to use or copy this program
  11  * for any purpose,  provided the above notices are retained on all copies.
  12  * Permission to modify the code and to distribute modified code is granted,
  13  * provided the above notices are retained, and a notice that the code was
  14  * modified is included with the above copyright notice.
  15  */
  16
  17 /* #define DEBUG */
  18 #include <stdio.h>
  19 #include "private/gc_priv.h"
  20
  21 GC_bool GC_use_entire_heap = 0;
  22
  23 /*
  24  * Free heap blocks are kept on one of several free lists,
  25  * depending on the size of the block.  Each free list is doubly linked.
  26  * Adjacent free blocks are coalesced.
  27  */
  28
  29
  30 # define MAX_BLACK_LIST_ALLOC (2*HBLKSIZE)
  31                 /* largest block we will allocate starting on a black   */
  32                 /* listed block.  Must be >= HBLKSIZE.                  */
  33
  34
  35 # define UNIQUE_THRESHOLD 32
  36         /* Sizes up to this many HBLKs each have their own free list    */
  37 # define HUGE_THRESHOLD 256
  38         /* Sizes of at least this many heap blocks are mapped to a      */
  39         /* single free list.                                            */
  40 # define FL_COMPRESSION 8
  41         /* In between sizes map this many distinct sizes to a single    */
  42         /* bin.                                                         */
  43
  44 # define N_HBLK_FLS (HUGE_THRESHOLD - UNIQUE_THRESHOLD)/FL_COMPRESSION \
  45                                  + UNIQUE_THRESHOLD
  46
  47 struct hblk * GC_hblkfreelist[N_HBLK_FLS+1] = { 0 };
  48
  49 #ifndef USE_MUNMAP
  50
  51   word GC_free_bytes[N_HBLK_FLS+1] = { 0 };
  52         /* Number of free bytes on each list.   */
  53
  54   /* Is bytes + the number of free bytes on lists n .. N_HBLK_FLS       */
  55   /* > GC_max_large_allocd_bytes?                                       */
  56 # ifdef __GNUC__
  57   __inline__
  58 # endif
  59   static GC_bool GC_enough_large_bytes_left(bytes,n)
  60   word bytes;
  61   int n;
  62   {
  63     int i;
  64     for (i = N_HBLK_FLS; i >= n; --i) {
  65         bytes += GC_free_bytes[i];
  66         if (bytes > GC_max_large_allocd_bytes) return TRUE;
  67     }
  68     return FALSE;
  69   }
  70
  71 # define INCR_FREE_BYTES(n, b) GC_free_bytes[n] += (b);
  72
  73 # define FREE_ASSERT(e) GC_ASSERT(e)
  74
  75 #else /* USE_MUNMAP */
  76
  77 # define INCR_FREE_BYTES(n, b)
  78 # define FREE_ASSERT(e)
  79
  80 #endif /* USE_MUNMAP */
  81
  82 /* Map a number of blocks to the appropriate large block free list index. */
  83 int GC_hblk_fl_from_blocks(blocks_needed)
  84 word blocks_needed;
  85 {
  86     if (blocks_needed <= UNIQUE_THRESHOLD) return blocks_needed;
  87     if (blocks_needed >= HUGE_THRESHOLD) return N_HBLK_FLS;
  88     return (blocks_needed - UNIQUE_THRESHOLD)/FL_COMPRESSION
  89                                         + UNIQUE_THRESHOLD;
  90
  91 }
  92
  93 # define PHDR(hhdr) HDR(hhdr -> hb_prev)
  94 # define NHDR(hhdr) HDR(hhdr -> hb_next)
  95
  96 # ifdef USE_MUNMAP
  97 #   define IS_MAPPED(hhdr) (((hhdr) -> hb_flags & WAS_UNMAPPED) == 0)
  98 # else  /* !USE_MMAP */
  99 #   define IS_MAPPED(hhdr) 1
 100 # endif /* USE_MUNMAP */
 101
 102 # if !defined(NO_DEBUGGING)
 103 void GC_print_hblkfreelist()
 104 {
 105     struct hblk * h;
 106     word total_free = 0;
 107     hdr * hhdr;
 108     word sz;
 109     int i;
 110
 111     for (i = 0; i <= N_HBLK_FLS; ++i) {
 112       h = GC_hblkfreelist[i];
 113 #     ifdef USE_MUNMAP
 114         if (0 != h) GC_printf1("Free list %ld (Total size %ld):\n",
 115                                (unsigned long)i);
 116 #     else
 117         if (0 != h) GC_printf2("Free list %ld (Total size %ld):\n",
 118                                (unsigned long)i,
 119                                (unsigned long)GC_free_bytes[i]);
 120 #     endif
 121       while (h != 0) {
 122         hhdr = HDR(h);
 123         sz = hhdr -> hb_sz;
 124         GC_printf2("\t0x%lx size %lu ", (unsigned long)h, (unsigned long)sz);
 125         total_free += sz;
 126         if (GC_is_black_listed(h, HBLKSIZE) != 0) {
 127              GC_printf0("start black listed\n");
 128         } else if (GC_is_black_listed(h, hhdr -> hb_sz) != 0) {
 129              GC_printf0("partially black listed\n");
 130         } else {
 131              GC_printf0("not black listed\n");
 132         }
 133         h = hhdr -> hb_next;
 134       }
 135     }
 136     if (total_free != GC_large_free_bytes) {
 137         GC_printf1("GC_large_free_bytes = %lu (INCONSISTENT!!)\n",
 138                    (unsigned long) GC_large_free_bytes);
 139     }
 140     GC_printf1("Total of %lu bytes on free list\n", (unsigned long)total_free);
 141 }
 142
 143 /* Return the free list index on which the block described by the header */
 144 /* appears, or -1 if it appears nowhere.                                 */
 145 int free_list_index_of(wanted)
 146 hdr * wanted;
 147 {
 148     struct hblk * h;
 149     hdr * hhdr;
 150     int i;
 151
 152     for (i = 0; i <= N_HBLK_FLS; ++i) {
 153       h = GC_hblkfreelist[i];
 154       while (h != 0) {
 155         hhdr = HDR(h);
 156         if (hhdr == wanted) return i;
 157         h = hhdr -> hb_next;
 158       }
 159     }
 160     return -1;
 161 }
 162
 163 void GC_dump_regions()
 164 {
 165     unsigned i;
 166     ptr_t start, end;
 167     ptr_t p;
 168     size_t bytes;
 169     hdr *hhdr;
 170     for (i = 0; i < GC_n_heap_sects; ++i) {
 171         start = GC_heap_sects[i].hs_start;
 172         bytes = GC_heap_sects[i].hs_bytes;
 173         end = start + bytes;
 174         /* Merge in contiguous sections.        */
 175           while (i+1 < GC_n_heap_sects && GC_heap_sects[i+1].hs_start == end) {
 176             ++i;
 177             end = GC_heap_sects[i].hs_start + GC_heap_sects[i].hs_bytes;
 178           }
 179         GC_printf2("***Section from 0x%lx to 0x%lx\n", start, end);
 180         for (p = start; p < end;) {
 181             hhdr = HDR(p);
 182             GC_printf1("\t0x%lx ", (unsigned long)p);
 183             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
 184                 GC_printf1("Missing header!!\n", hhdr);
 185                 p += HBLKSIZE;
 186                 continue;
 187             }
 188             if (HBLK_IS_FREE(hhdr)) {
 189                 int correct_index = GC_hblk_fl_from_blocks(
 190                                         divHBLKSZ(hhdr -> hb_sz));
 191                 int actual_index;
 192
 193                 GC_printf1("\tfree block of size 0x%lx bytes",
 194                            (unsigned long)(hhdr -> hb_sz));
 195                 if (IS_MAPPED(hhdr)) {
 196                     GC_printf0("\n");
 197                 } else {
 198                     GC_printf0("(unmapped)\n");
 199                 }
 200                 actual_index = free_list_index_of(hhdr);
 201                 if (-1 == actual_index) {
 202                     GC_printf1("\t\tBlock not on free list %ld!!\n",
 203                                 correct_index);
 204                 } else if (correct_index != actual_index) {
 205                     GC_printf2("\t\tBlock on list %ld, should be on %ld!!\n",
 206                                actual_index, correct_index);
 207                 }
 208                 p += hhdr -> hb_sz;
 209             } else {
 210                 GC_printf1("\tused for blocks of size 0x%lx bytes\n",
 211                            (unsigned long)WORDS_TO_BYTES(hhdr -> hb_sz));
 212                 p += HBLKSIZE * OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
 213             }
 214         }
 215     }
 216 }
 217
 218 # endif /* NO_DEBUGGING */
 219
 220 /* Initialize hdr for a block containing the indicated size and         */
 221 /* kind of objects.                                                     */
 222 /* Return FALSE on failure.                                             */
 223 static GC_bool setup_header(hhdr, sz, kind, flags)
 224 register hdr * hhdr;
 225 word sz;        /* object size in words */
 226 int kind;
 227 unsigned char flags;
 228 {
 229     register word descr;
 230
 231     /* Add description of valid object pointers */
 232       if (!GC_add_map_entry(sz)) return(FALSE);
 233       hhdr -> hb_map = GC_obj_map[sz > MAXOBJSZ? 0 : sz];
 234
 235     /* Set size, kind and mark proc fields */
 236       hhdr -> hb_sz = sz;
 237       hhdr -> hb_obj_kind = kind;
 238       hhdr -> hb_flags = flags;
 239       descr = GC_obj_kinds[kind].ok_descriptor;
 240       if (GC_obj_kinds[kind].ok_relocate_descr) descr += WORDS_TO_BYTES(sz);
 241       hhdr -> hb_descr = descr;
 242
 243     /* Clear mark bits */
 244       GC_clear_hdr_marks(hhdr);
 245
 246     hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
 247     return(TRUE);
 248 }
 249
 250 #define FL_UNKNOWN -1
 251 /*
 252  * Remove hhdr from the appropriate free list.
 253  * We assume it is on the nth free list, or on the size
 254  * appropriate free list if n is FL_UNKNOWN.
 255  */
 256 void GC_remove_from_fl(hhdr, n)
 257 hdr * hhdr;
 258 int n;
 259 {
 260     int index;
 261
 262     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 263 #   ifndef USE_MUNMAP
 264       /* We always need index to mainatin free counts.  */
 265       if (FL_UNKNOWN == n) {
 266           index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 267       } else {
 268           index = n;
 269       }
 270 #   endif
 271     if (hhdr -> hb_prev == 0) {
 272 #       ifdef USE_MUNMAP
 273           if (FL_UNKNOWN == n) {
 274             index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 275           } else {
 276             index = n;
 277           }
 278 #       endif
 279         GC_ASSERT(HDR(GC_hblkfreelist[index]) == hhdr);
 280         GC_hblkfreelist[index] = hhdr -> hb_next;
 281     } else {
 282         hdr *phdr;
 283         GET_HDR(hhdr -> hb_prev, phdr);
 284         phdr -> hb_next = hhdr -> hb_next;
 285     }
 286     INCR_FREE_BYTES(index, - (signed_word)(hhdr -> hb_sz));
 287     FREE_ASSERT(GC_free_bytes[index] >= 0);
 288     if (0 != hhdr -> hb_next) {
 289         hdr * nhdr;
 290         GC_ASSERT(!IS_FORWARDING_ADDR_OR_NIL(NHDR(hhdr)));
 291         GET_HDR(hhdr -> hb_next, nhdr);
 292         nhdr -> hb_prev = hhdr -> hb_prev;
 293     }
 294 }
 295
 296 /*
 297  * Return a pointer to the free block ending just before h, if any.
 298  */
 299 struct hblk * GC_free_block_ending_at(h)
 300 struct hblk *h;
 301 {
 302     struct hblk * p = h - 1;
 303     hdr * phdr;
 304
 305     GET_HDR(p, phdr);
 306     while (0 != phdr && IS_FORWARDING_ADDR_OR_NIL(phdr)) {
 307         p = FORWARDED_ADDR(p,phdr);
 308         phdr = HDR(p);
 309     }
 310     if (0 != phdr) {
 311         if(HBLK_IS_FREE(phdr)) {
 312             return p;
 313         } else {
 314             return 0;
 315         }
 316     }
 317     p = GC_prev_block(h - 1);
 318     if (0 != p) {
 319       phdr = HDR(p);
 320       if (HBLK_IS_FREE(phdr) && (ptr_t)p + phdr -> hb_sz == (ptr_t)h) {
 321         return p;
 322       }
 323     }
 324     return 0;
 325 }
 326
 327 /*
 328  * Add hhdr to the appropriate free list.
 329  * We maintain individual free lists sorted by address.
 330  */
 331 void GC_add_to_fl(h, hhdr)
 332 struct hblk *h;
 333 hdr * hhdr;
 334 {
 335     int index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 336     struct hblk *second = GC_hblkfreelist[index];
 337     hdr * second_hdr;
 338 #   ifdef GC_ASSERTIONS
 339       struct hblk *next = (struct hblk *)((word)h + hhdr -> hb_sz);
 340       hdr * nexthdr = HDR(next);
 341       struct hblk *prev = GC_free_block_ending_at(h);
 342       hdr * prevhdr = HDR(prev);
 343       GC_ASSERT(nexthdr == 0 || !HBLK_IS_FREE(nexthdr) || !IS_MAPPED(nexthdr));
 344       GC_ASSERT(prev == 0 || !HBLK_IS_FREE(prevhdr) || !IS_MAPPED(prevhdr));
 345 #   endif
 346     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 347     GC_hblkfreelist[index] = h;
 348     INCR_FREE_BYTES(index, hhdr -> hb_sz);
 349     FREE_ASSERT(GC_free_bytes[index] <= GC_large_free_bytes)
 350     hhdr -> hb_next = second;
 351     hhdr -> hb_prev = 0;
 352     if (0 != second) {
 353       GET_HDR(second, second_hdr);
 354       second_hdr -> hb_prev = h;
 355     }
 356     GC_invalidate_map(hhdr);
 357 }
 358
 359 #ifdef USE_MUNMAP
 360
 361 /* Unmap blocks that haven't been recently touched.  This is the only way */
 362 /* way blocks are ever unmapped.                                          */
 363 void GC_unmap_old(void)
 364 {
 365     struct hblk * h;
 366     hdr * hhdr;
 367     word sz;
 368     unsigned short last_rec, threshold;
 369     int i;
 370 #   define UNMAP_THRESHOLD 6
 371
 372     for (i = 0; i <= N_HBLK_FLS; ++i) {
 373       for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
 374         hhdr = HDR(h);
 375         if (!IS_MAPPED(hhdr)) continue;
 376         threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
 377         last_rec = hhdr -> hb_last_reclaimed;
 378         if ((last_rec > GC_gc_no || last_rec < threshold)
 379             && threshold < GC_gc_no /* not recently wrapped */) {
 380           sz = hhdr -> hb_sz;
 381           GC_unmap((ptr_t)h, sz);
 382           hhdr -> hb_flags |= WAS_UNMAPPED;
 383         }
 384       }
 385     }
 386 }
 387
 388 /* Merge all unmapped blocks that are adjacent to other free            */
 389 /* blocks.  This may involve remapping, since all blocks are either     */
 390 /* fully mapped or fully unmapped.                                      */
 391 void GC_merge_unmapped(void)
 392 {
 393     struct hblk * h, *next;
 394     hdr * hhdr, *nexthdr;
 395     word size, nextsize;
 396     int i;
 397
 398     for (i = 0; i <= N_HBLK_FLS; ++i) {
 399       h = GC_hblkfreelist[i];
 400       while (h != 0) {
 401         GET_HDR(h, hhdr);
 402         size = hhdr->hb_sz;
 403         next = (struct hblk *)((word)h + size);
 404         GET_HDR(next, nexthdr);
 405         /* Coalesce with successor, if possible */
 406           if (0 != nexthdr && HBLK_IS_FREE(nexthdr)) {
 407             nextsize = nexthdr -> hb_sz;
 408             if (IS_MAPPED(hhdr)) {
 409               GC_ASSERT(!IS_MAPPED(nexthdr));
 410               /* make both consistent, so that we can merge */
 411                 if (size > nextsize) {
 412                   GC_remap((ptr_t)next, nextsize);
 413                 } else {
 414                   GC_unmap((ptr_t)h, size);
 415                   hhdr -> hb_flags |= WAS_UNMAPPED;
 416                 }
 417             } else if (IS_MAPPED(nexthdr)) {
 418               GC_ASSERT(!IS_MAPPED(hhdr));
 419               if (size > nextsize) {
 420                 GC_unmap((ptr_t)next, nextsize);
 421               } else {
 422                 GC_remap((ptr_t)h, size);
 423                 hhdr -> hb_flags &= ~WAS_UNMAPPED;
 424                 hhdr -> hb_last_reclaimed = nexthdr -> hb_last_reclaimed;
 425               }
 426             } else {
 427               /* Unmap any gap in the middle */
 428                 GC_unmap_gap((ptr_t)h, size, (ptr_t)next, nexthdr -> hb_sz);
 429             }
 430             /* If they are both unmapped, we merge, but leave unmapped. */
 431             GC_remove_from_fl(hhdr, i);
 432             GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 433             hhdr -> hb_sz += nexthdr -> hb_sz;
 434             GC_remove_header(next);
 435             GC_add_to_fl(h, hhdr);
 436             /* Start over at beginning of list */
 437             h = GC_hblkfreelist[i];
 438           } else /* not mergable with successor */ {
 439             h = hhdr -> hb_next;
 440           }
 441       } /* while (h != 0) ... */
 442     } /* for ... */
 443 }
 444
 445 #endif /* USE_MUNMAP */
 446
 447 /*
 448  * Return a pointer to a block starting at h of length bytes.
 449  * Memory for the block is mapped.
 450  * Remove the block from its free list, and return the remainder (if any)
 451  * to its appropriate free list.
 452  * May fail by returning 0.
 453  * The header for the returned block must be set up by the caller.
 454  * If the return value is not 0, then hhdr is the header for it.
 455  */
 456 struct hblk * GC_get_first_part(h, hhdr, bytes, index)
 457 struct hblk *h;
 458 hdr * hhdr;
 459 word bytes;
 460 int index;
 461 {
 462     word total_size = hhdr -> hb_sz;
 463     struct hblk * rest;
 464     hdr * rest_hdr;
 465
 466     GC_ASSERT((total_size & (HBLKSIZE-1)) == 0);
 467     GC_remove_from_fl(hhdr, index);
 468     if (total_size == bytes) return h;
 469     rest = (struct hblk *)((word)h + bytes);
 470     rest_hdr = GC_install_header(rest);
 471     if (0 == rest_hdr) return(0);
 472     rest_hdr -> hb_sz = total_size - bytes;
 473     rest_hdr -> hb_flags = 0;
 474 #   ifdef GC_ASSERTIONS
 475       /* Mark h not free, to avoid assertion about adjacent free blocks. */
 476         hhdr -> hb_map = 0;
 477 #   endif
 478     GC_add_to_fl(rest, rest_hdr);
 479     return h;
 480 }
 481
 482 /*
 483  * H is a free block.  N points at an address inside it.
 484  * A new header for n has already been set up.  Fix up h's header
 485  * to reflect the fact that it is being split, move it to the
 486  * appropriate free list.
 487  * N replaces h in the original free list.
 488  *
 489  * Nhdr is not completely filled in, since it is about to allocated.
 490  * It may in fact end up on the wrong free list for its size.
 491  * (Hence adding it to a free list is silly.  But this path is hopefully
 492  * rare enough that it doesn't matter.  The code is cleaner this way.)
 493  */
 494 void GC_split_block(h, hhdr, n, nhdr, index)
 495 struct hblk *h;
 496 hdr * hhdr;
 497 struct hblk *n;
 498 hdr * nhdr;
 499 int index;      /* Index of free list */
 500 {
 501     word total_size = hhdr -> hb_sz;
 502     word h_size = (word)n - (word)h;
 503     struct hblk *prev = hhdr -> hb_prev;
 504     struct hblk *next = hhdr -> hb_next;
 505
 506     /* Replace h with n on its freelist */
 507       nhdr -> hb_prev = prev;
 508       nhdr -> hb_next = next;
 509       nhdr -> hb_sz = total_size - h_size;
 510       nhdr -> hb_flags = 0;
 511       if (0 != prev) {
 512         HDR(prev) -> hb_next = n;
 513       } else {
 514         GC_hblkfreelist[index] = n;
 515       }
 516       if (0 != next) {
 517         HDR(next) -> hb_prev = n;
 518       }
 519       INCR_FREE_BYTES(index, -(signed_word)h_size);
 520       FREE_ASSERT(GC_free_bytes[index] > 0);
 521 #     ifdef GC_ASSERTIONS
 522         nhdr -> hb_map = 0;     /* Don't fail test for consecutive      */
 523                                 /* free blocks in GC_add_to_fl.         */
 524 #     endif
 525 #   ifdef USE_MUNMAP
 526       hhdr -> hb_last_reclaimed = GC_gc_no;
 527 #   endif
 528     hhdr -> hb_sz = h_size;
 529     GC_add_to_fl(h, hhdr);
 530     GC_invalidate_map(nhdr);
 531 }
 532
 533 struct hblk * GC_allochblk_nth();
 534
 535 /*
 536  * Allocate (and return pointer to) a heap block
 537  *   for objects of size sz words, searching the nth free list.
 538  *
 539  * NOTE: We set obj_map field in header correctly.
 540  *       Caller is responsible for building an object freelist in block.
 541  *
 542  * Unlike older versions of the collectors, the client is responsible
 543  * for clearing the block, if necessary.
 544  */
 545 struct hblk *
 546 GC_allochblk(sz, kind, flags)
 547 word sz;
 548 int kind;
 549 unsigned flags;  /* IGNORE_OFF_PAGE or 0 */
 550 {
 551     word blocks = OBJ_SZ_TO_BLOCKS(sz);
 552     int start_list = GC_hblk_fl_from_blocks(blocks);
 553     int i;
 554     for (i = start_list; i <= N_HBLK_FLS; ++i) {
 555         struct hblk * result = GC_allochblk_nth(sz, kind, flags, i);
 556         if (0 != result) {
 557             return result;
 558         }
 559     }
 560     return 0;
 561 }
 562 /*
 563  * The same, but with search restricted to nth free list.
 564  */
 565 struct hblk *
 566 GC_allochblk_nth(sz, kind, flags, n)
 567 word sz;
 568 int kind;
 569 unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
 570 int n;
 571 {
 572     register struct hblk *hbp;
 573     register hdr * hhdr;                /* Header corr. to hbp */
 574     register struct hblk *thishbp;
 575     register hdr * thishdr;             /* Header corr. to hbp */
 576     signed_word size_needed;    /* number of bytes in requested objects */
 577     signed_word size_avail;     /* bytes available in this block        */
 578
 579     size_needed = HBLKSIZE * OBJ_SZ_TO_BLOCKS(sz);
 580
 581     /* search for a big enough block in free list */
 582         hbp = GC_hblkfreelist[n];
 583         for(; 0 != hbp; hbp = hhdr -> hb_next) {
 584             GET_HDR(hbp, hhdr);
 585             size_avail = hhdr->hb_sz;
 586             if (size_avail < size_needed) continue;
 587             if (!GC_use_entire_heap
 588                 && size_avail != size_needed
 589                 && USED_HEAP_SIZE >= GC_requested_heapsize
 590                 && !TRUE_INCREMENTAL && GC_should_collect()) {
 591 #               ifdef USE_MUNMAP
 592                     continue;
 593 #               else
 594                     /* If we have enough large blocks left to cover any */
 595                     /* previous request for large blocks, we go ahead   */
 596                     /* and split.  Assuming a steady state, that should */
 597                     /* be safe.  It means that we can use the full      */
 598                     /* heap if we allocate only small objects.          */
 599                     if (!GC_enough_large_bytes_left(GC_large_allocd_bytes, n)) {
 600                       continue;
 601                     }
 602                     /* If we are deallocating lots of memory from       */
 603                     /* finalizers, fail and collect sooner rather       */
 604                     /* than later.                                      */
 605                     if (GC_finalizer_mem_freed > (GC_heapsize >> 4))  {
 606                       continue;
 607                     }
 608 #               endif /* !USE_MUNMAP */
 609             }
 610             /* If the next heap block is obviously better, go on.       */
 611             /* This prevents us from disassembling a single large block */
 612             /* to get tiny blocks.                                      */
 613             {
 614               signed_word next_size;
 615
 616               thishbp = hhdr -> hb_next;
 617               if (thishbp != 0) {
 618                 GET_HDR(thishbp, thishdr);
 619                 next_size = (signed_word)(thishdr -> hb_sz);
 620                 if (next_size < size_avail
 621                   && next_size >= size_needed
 622                   && !GC_is_black_listed(thishbp, (word)size_needed)) {
 623                   continue;
 624                 }
 625               }
 626             }
 627             if ( !IS_UNCOLLECTABLE(kind) &&
 628                  (kind != PTRFREE || size_needed > MAX_BLACK_LIST_ALLOC)) {
 629               struct hblk * lasthbp = hbp;
 630               ptr_t search_end = (ptr_t)hbp + size_avail - size_needed;
 631               signed_word orig_avail = size_avail;
 632               signed_word eff_size_needed = ((flags & IGNORE_OFF_PAGE)?
 633                                                 HBLKSIZE
 634                                                 : size_needed);
 635
 636
 637               while ((ptr_t)lasthbp <= search_end
 638                      && (thishbp = GC_is_black_listed(lasthbp,
 639                                                       (word)eff_size_needed))
 640                         != 0) {
 641                 lasthbp = thishbp;
 642               }
 643               size_avail -= (ptr_t)lasthbp - (ptr_t)hbp;
 644               thishbp = lasthbp;
 645               if (size_avail >= size_needed) {
 646                 if (thishbp != hbp &&
 647                     0 != (thishdr = GC_install_header(thishbp))) {
 648                   /* Make sure it's mapped before we mangle it. */
 649 #                   ifdef USE_MUNMAP
 650                       if (!IS_MAPPED(hhdr)) {
 651                         GC_remap((ptr_t)hbp, hhdr -> hb_sz);
 652                         hhdr -> hb_flags &= ~WAS_UNMAPPED;
 653                       }
 654 #                   endif
 655                   /* Split the block at thishbp */
 656                       GC_split_block(hbp, hhdr, thishbp, thishdr, n);
 657                   /* Advance to thishbp */
 658                       hbp = thishbp;
 659                       hhdr = thishdr;
 660                       /* We must now allocate thishbp, since it may     */
 661                       /* be on the wrong free list.                     */
 662                 }
 663               } else if (size_needed > (signed_word)BL_LIMIT
 664                          && orig_avail - size_needed
 665                             > (signed_word)BL_LIMIT) {
 666                 /* Punt, since anything else risks unreasonable heap growth. */
 667                 if (++GC_large_alloc_warn_suppressed
 668                     >= GC_large_alloc_warn_interval) {
 669                   WARN("Repeated allocation of very large block "
 670                        "(appr. size %ld):\n"
 671                        "\tMay lead to memory leak and poor performance.\n",
 672                        size_needed);
 673                   GC_large_alloc_warn_suppressed = 0;
 674                 }
 675                 size_avail = orig_avail;
 676               } else if (size_avail == 0 && size_needed == HBLKSIZE
 677                          && IS_MAPPED(hhdr)) {
 678                 if (!GC_find_leak) {
 679                   static unsigned count = 0;
 680
 681                   /* The block is completely blacklisted.  We need      */
 682                   /* to drop some such blocks, since otherwise we spend */
 683                   /* all our time traversing them if pointerfree        */
 684                   /* blocks are unpopular.                              */
 685                   /* A dropped block will be reconsidered at next GC.   */
 686                   if ((++count & 3) == 0) {
 687                     /* Allocate and drop the block in small chunks, to  */
 688                     /* maximize the chance that we will recover some    */
 689                     /* later.                                           */
 690                       word total_size = hhdr -> hb_sz;
 691                       struct hblk * limit = hbp + divHBLKSZ(total_size);
 692                       struct hblk * h;
 693                       struct hblk * prev = hhdr -> hb_prev;
 694
 695                       GC_words_wasted += total_size;
 696                       GC_large_free_bytes -= total_size;
 697                       GC_remove_from_fl(hhdr, n);
 698                       for (h = hbp; h < limit; h++) {
 699                         if (h == hbp || 0 != (hhdr = GC_install_header(h))) {
 700                           (void) setup_header(
 701                                   hhdr,
 702                                   BYTES_TO_WORDS(HBLKSIZE),
 703                                   PTRFREE, 0); /* Cant fail */
 704                           if (GC_debugging_started) {
 705                             BZERO(h, HBLKSIZE);
 706                           }
 707                         }
 708                       }
 709                     /* Restore hbp to point at free block */
 710                       hbp = prev;
 711                       if (0 == hbp) {
 712                         return GC_allochblk_nth(sz, kind, flags, n);
 713                       }
 714                       hhdr = HDR(hbp);
 715                   }
 716                 }
 717               }
 718             }
 719             if( size_avail >= size_needed ) {
 720 #               ifdef USE_MUNMAP
 721                   if (!IS_MAPPED(hhdr)) {
 722                     GC_remap((ptr_t)hbp, hhdr -> hb_sz);
 723                     hhdr -> hb_flags &= ~WAS_UNMAPPED;
 724                   }
 725 #               endif
 726                 /* hbp may be on the wrong freelist; the parameter n    */
 727                 /* is important.                                        */
 728                 hbp = GC_get_first_part(hbp, hhdr, size_needed, n);
 729                 break;
 730             }
 731         }
 732
 733     if (0 == hbp) return 0;
 734
 735     /* Add it to map of valid blocks */
 736         if (!GC_install_counts(hbp, (word)size_needed)) return(0);
 737         /* This leaks memory under very rare conditions. */
 738
 739     /* Set up header */
 740         if (!setup_header(hhdr, sz, kind, flags)) {
 741             GC_remove_counts(hbp, (word)size_needed);
 742             return(0); /* ditto */
 743         }
 744
 745     /* Notify virtual dirty bit implementation that we are about to write.  */
 746     /* Ensure that pointerfree objects are not protected if it's avoidable. */
 747         GC_remove_protection(hbp, divHBLKSZ(size_needed),
 748                              (hhdr -> hb_descr == 0) /* pointer-free */);
 749
 750     /* We just successfully allocated a block.  Restart count of        */
 751     /* consecutive failures.                                            */
 752     {
 753         extern unsigned GC_fail_count;
 754
 755         GC_fail_count = 0;
 756     }
 757
 758     GC_large_free_bytes -= size_needed;
 759
 760     GC_ASSERT(IS_MAPPED(hhdr));
 761     return( hbp );
 762 }
 763
 764 struct hblk * GC_freehblk_ptr = 0;  /* Search position hint for GC_freehblk */
 765
 766 /*
 767  * Free a heap block.
 768  *
 769  * Coalesce the block with its neighbors if possible.
 770  *
 771  * All mark words are assumed to be cleared.
 772  */
 773 void
 774 GC_freehblk(hbp)
 775 struct hblk *hbp;
 776 {
 777 struct hblk *next, *prev;
 778 hdr *hhdr, *prevhdr, *nexthdr;
 779 signed_word size;
 780
 781
 782     GET_HDR(hbp, hhdr);
 783     size = hhdr->hb_sz;
 784     size = HBLKSIZE * OBJ_SZ_TO_BLOCKS(size);
 785     GC_remove_counts(hbp, (word)size);
 786     hhdr->hb_sz = size;
 787 #   ifdef USE_MUNMAP
 788       hhdr -> hb_last_reclaimed = GC_gc_no;
 789 #   endif
 790
 791     /* Check for duplicate deallocation in the easy case */
 792       if (HBLK_IS_FREE(hhdr)) {
 793         GC_printf1("Duplicate large block deallocation of 0x%lx\n",
 794                    (unsigned long) hbp);
 795         ABORT("Duplicate large block deallocation");
 796       }
 797
 798     GC_ASSERT(IS_MAPPED(hhdr));
 799     GC_invalidate_map(hhdr);
 800     next = (struct hblk *)((word)hbp + size);
 801     GET_HDR(next, nexthdr);
 802     prev = GC_free_block_ending_at(hbp);
 803     /* Coalesce with successor, if possible */
 804       if(0 != nexthdr && HBLK_IS_FREE(nexthdr) && IS_MAPPED(nexthdr)) {
 805         GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 806         hhdr -> hb_sz += nexthdr -> hb_sz;
 807         GC_remove_header(next);
 808       }
 809     /* Coalesce with predecessor, if possible. */
 810       if (0 != prev) {
 811         prevhdr = HDR(prev);
 812         if (IS_MAPPED(prevhdr)) {
 813           GC_remove_from_fl(prevhdr, FL_UNKNOWN);
 814           prevhdr -> hb_sz += hhdr -> hb_sz;
 815 #         ifdef USE_MUNMAP
 816             prevhdr -> hb_last_reclaimed = GC_gc_no;
 817 #         endif
 818           GC_remove_header(hbp);
 819           hbp = prev;
 820           hhdr = prevhdr;
 821         }
 822       }
 823     /* FIXME: It is not clear we really always want to do these merges  */
 824     /* with -DUSE_MUNMAP, since it updates ages and hence prevents      */
 825     /* unmapping.                                                       */
 826
 827     GC_large_free_bytes += size;
 828     GC_add_to_fl(hbp, hhdr);
 829 }
 830