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:\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 #   ifndef USE_MUNMAP
 137       if (total_free != GC_large_free_bytes) {
 138         GC_printf1("GC_large_free_bytes = %lu (INCONSISTENT!!)\n",
 139                    (unsigned long) GC_large_free_bytes);
 140       }
 141 #   endif
 142     GC_printf1("Total of %lu bytes on free list\n", (unsigned long)total_free);
 143 }
 144
 145 /* Return the free list index on which the block described by the header */
 146 /* appears, or -1 if it appears nowhere.                                 */
 147 int free_list_index_of(wanted)
 148 hdr * wanted;
 149 {
 150     struct hblk * h;
 151     hdr * hhdr;
 152     int i;
 153
 154     for (i = 0; i <= N_HBLK_FLS; ++i) {
 155       h = GC_hblkfreelist[i];
 156       while (h != 0) {
 157         hhdr = HDR(h);
 158         if (hhdr == wanted) return i;
 159         h = hhdr -> hb_next;
 160       }
 161     }
 162     return -1;
 163 }
 164
 165 void GC_dump_regions()
 166 {
 167     unsigned i;
 168     ptr_t start, end;
 169     ptr_t p;
 170     size_t bytes;
 171     hdr *hhdr;
 172     for (i = 0; i < GC_n_heap_sects; ++i) {
 173         start = GC_heap_sects[i].hs_start;
 174         bytes = GC_heap_sects[i].hs_bytes;
 175         end = start + bytes;
 176         /* Merge in contiguous sections.        */
 177           while (i+1 < GC_n_heap_sects && GC_heap_sects[i+1].hs_start == end) {
 178             ++i;
 179             end = GC_heap_sects[i].hs_start + GC_heap_sects[i].hs_bytes;
 180           }
 181         GC_printf2("***Section from 0x%lx to 0x%lx\n", start, end);
 182         for (p = start; p < end;) {
 183             hhdr = HDR(p);
 184             GC_printf1("\t0x%lx ", (unsigned long)p);
 185             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
 186                 GC_printf1("Missing header!!(%ld)\n", hhdr);
 187                 p += HBLKSIZE;
 188                 continue;
 189             }
 190             if (HBLK_IS_FREE(hhdr)) {
 191                 int correct_index = GC_hblk_fl_from_blocks(
 192                                         divHBLKSZ(hhdr -> hb_sz));
 193                 int actual_index;
 194
 195                 GC_printf1("\tfree block of size 0x%lx bytes",
 196                            (unsigned long)(hhdr -> hb_sz));
 197                 if (IS_MAPPED(hhdr)) {
 198                     GC_printf0("\n");
 199                 } else {
 200                     GC_printf0("(unmapped)\n");
 201                 }
 202                 actual_index = free_list_index_of(hhdr);
 203                 if (-1 == actual_index) {
 204                     GC_printf1("\t\tBlock not on free list %ld!!\n",
 205                                 correct_index);
 206                 } else if (correct_index != actual_index) {
 207                     GC_printf2("\t\tBlock on list %ld, should be on %ld!!\n",
 208                                actual_index, correct_index);
 209                 }
 210                 p += hhdr -> hb_sz;
 211             } else {
 212                 GC_printf1("\tused for blocks of size 0x%lx bytes\n",
 213                            (unsigned long)WORDS_TO_BYTES(hhdr -> hb_sz));
 214                 p += HBLKSIZE * OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
 215             }
 216         }
 217     }
 218 }
 219
 220 # endif /* NO_DEBUGGING */
 221
 222 /* Initialize hdr for a block containing the indicated size and         */
 223 /* kind of objects.                                                     */
 224 /* Return FALSE on failure.                                             */
 225 static GC_bool setup_header(hhdr, sz, kind, flags)
 226 register hdr * hhdr;
 227 word sz;        /* object size in words */
 228 int kind;
 229 unsigned char flags;
 230 {
 231     register word descr;
 232
 233     /* Add description of valid object pointers */
 234       if (!GC_add_map_entry(sz)) return(FALSE);
 235       hhdr -> hb_map = GC_obj_map[sz > MAXOBJSZ? 0 : sz];
 236
 237     /* Set size, kind and mark proc fields */
 238       hhdr -> hb_sz = sz;
 239       hhdr -> hb_obj_kind = kind;
 240       hhdr -> hb_flags = flags;
 241       descr = GC_obj_kinds[kind].ok_descriptor;
 242       if (GC_obj_kinds[kind].ok_relocate_descr) descr += WORDS_TO_BYTES(sz);
 243       hhdr -> hb_descr = descr;
 244
 245     /* Clear mark bits */
 246       GC_clear_hdr_marks(hhdr);
 247
 248     hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
 249     return(TRUE);
 250 }
 251
 252 #define FL_UNKNOWN -1
 253 /*
 254  * Remove hhdr from the appropriate free list.
 255  * We assume it is on the nth free list, or on the size
 256  * appropriate free list if n is FL_UNKNOWN.
 257  */
 258 void GC_remove_from_fl(hhdr, n)
 259 hdr * hhdr;
 260 int n;
 261 {
 262     int index;
 263
 264     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 265 #   ifndef USE_MUNMAP
 266       /* We always need index to mainatin free counts.  */
 267       if (FL_UNKNOWN == n) {
 268           index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 269       } else {
 270           index = n;
 271       }
 272 #   endif
 273     if (hhdr -> hb_prev == 0) {
 274 #       ifdef USE_MUNMAP
 275           if (FL_UNKNOWN == n) {
 276             index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 277           } else {
 278             index = n;
 279           }
 280 #       endif
 281         GC_ASSERT(HDR(GC_hblkfreelist[index]) == hhdr);
 282         GC_hblkfreelist[index] = hhdr -> hb_next;
 283     } else {
 284         hdr *phdr;
 285         GET_HDR(hhdr -> hb_prev, phdr);
 286         phdr -> hb_next = hhdr -> hb_next;
 287     }
 288     FREE_ASSERT(GC_free_bytes[index] >= hhdr -> hb_sz);
 289     INCR_FREE_BYTES(index, - (signed_word)(hhdr -> hb_sz));
 290     if (0 != hhdr -> hb_next) {
 291         hdr * nhdr;
 292         GC_ASSERT(!IS_FORWARDING_ADDR_OR_NIL(NHDR(hhdr)));
 293         GET_HDR(hhdr -> hb_next, nhdr);
 294         nhdr -> hb_prev = hhdr -> hb_prev;
 295     }
 296 }
 297
 298 /*
 299  * Return a pointer to the free block ending just before h, if any.
 300  */
 301 struct hblk * GC_free_block_ending_at(h)
 302 struct hblk *h;
 303 {
 304     struct hblk * p = h - 1;
 305     hdr * phdr;
 306
 307     GET_HDR(p, phdr);
 308     while (0 != phdr && IS_FORWARDING_ADDR_OR_NIL(phdr)) {
 309         p = FORWARDED_ADDR(p,phdr);
 310         phdr = HDR(p);
 311     }
 312     if (0 != phdr) {
 313         if(HBLK_IS_FREE(phdr)) {
 314             return p;
 315         } else {
 316             return 0;
 317         }
 318     }
 319     p = GC_prev_block(h - 1);
 320     if (0 != p) {
 321       phdr = HDR(p);
 322       if (HBLK_IS_FREE(phdr) && (ptr_t)p + phdr -> hb_sz == (ptr_t)h) {
 323         return p;
 324       }
 325     }
 326     return 0;
 327 }
 328
 329 /*
 330  * Add hhdr to the appropriate free list.
 331  * We maintain individual free lists sorted by address.
 332  */
 333 void GC_add_to_fl(h, hhdr)
 334 struct hblk *h;
 335 hdr * hhdr;
 336 {
 337     int index = GC_hblk_fl_from_blocks(divHBLKSZ(hhdr -> hb_sz));
 338     struct hblk *second = GC_hblkfreelist[index];
 339     hdr * second_hdr;
 340 #   ifdef GC_ASSERTIONS
 341       struct hblk *next = (struct hblk *)((word)h + hhdr -> hb_sz);
 342       hdr * nexthdr = HDR(next);
 343       struct hblk *prev = GC_free_block_ending_at(h);
 344       hdr * prevhdr = HDR(prev);
 345       GC_ASSERT(nexthdr == 0 || !HBLK_IS_FREE(nexthdr) || !IS_MAPPED(nexthdr));
 346       GC_ASSERT(prev == 0 || !HBLK_IS_FREE(prevhdr) || !IS_MAPPED(prevhdr));
 347 #   endif
 348     GC_ASSERT(((hhdr -> hb_sz) & (HBLKSIZE-1)) == 0);
 349     GC_hblkfreelist[index] = h;
 350     INCR_FREE_BYTES(index, hhdr -> hb_sz);
 351     FREE_ASSERT(GC_free_bytes[index] <= GC_large_free_bytes)
 352     hhdr -> hb_next = second;
 353     hhdr -> hb_prev = 0;
 354     if (0 != second) {
 355       GET_HDR(second, second_hdr);
 356       second_hdr -> hb_prev = h;
 357     }
 358     GC_invalidate_map(hhdr);
 359 }
 360
 361 #ifdef USE_MUNMAP
 362
 363 /* Unmap blocks that haven't been recently touched.  This is the only way */
 364 /* way blocks are ever unmapped.                                          */
 365 void GC_unmap_old(void)
 366 {
 367     struct hblk * h;
 368     hdr * hhdr;
 369     word sz;
 370     unsigned short last_rec, threshold;
 371     int i;
 372 #   define UNMAP_THRESHOLD 6
 373
 374     for (i = 0; i <= N_HBLK_FLS; ++i) {
 375       for (h = GC_hblkfreelist[i]; 0 != h; h = hhdr -> hb_next) {
 376         hhdr = HDR(h);
 377         if (!IS_MAPPED(hhdr)) continue;
 378         threshold = (unsigned short)(GC_gc_no - UNMAP_THRESHOLD);
 379         last_rec = hhdr -> hb_last_reclaimed;
 380         if ((last_rec > GC_gc_no || last_rec < threshold)
 381             && threshold < GC_gc_no /* not recently wrapped */) {
 382           sz = hhdr -> hb_sz;
 383           GC_unmap((ptr_t)h, sz);
 384           hhdr -> hb_flags |= WAS_UNMAPPED;
 385         }
 386       }
 387     }
 388 }
 389
 390 /* Merge all unmapped blocks that are adjacent to other free            */
 391 /* blocks.  This may involve remapping, since all blocks are either     */
 392 /* fully mapped or fully unmapped.                                      */
 393 void GC_merge_unmapped(void)
 394 {
 395     struct hblk * h, *next;
 396     hdr * hhdr, *nexthdr;
 397     word size, nextsize;
 398     int i;
 399
 400     for (i = 0; i <= N_HBLK_FLS; ++i) {
 401       h = GC_hblkfreelist[i];
 402       while (h != 0) {
 403         GET_HDR(h, hhdr);
 404         size = hhdr->hb_sz;
 405         next = (struct hblk *)((word)h + size);
 406         GET_HDR(next, nexthdr);
 407         /* Coalesce with successor, if possible */
 408           if (0 != nexthdr && HBLK_IS_FREE(nexthdr)) {
 409             nextsize = nexthdr -> hb_sz;
 410             if (IS_MAPPED(hhdr)) {
 411               GC_ASSERT(!IS_MAPPED(nexthdr));
 412               /* make both consistent, so that we can merge */
 413                 if (size > nextsize) {
 414                   GC_remap((ptr_t)next, nextsize);
 415                 } else {
 416                   GC_unmap((ptr_t)h, size);
 417                   hhdr -> hb_flags |= WAS_UNMAPPED;
 418                 }
 419             } else if (IS_MAPPED(nexthdr)) {
 420               GC_ASSERT(!IS_MAPPED(hhdr));
 421               if (size > nextsize) {
 422                 GC_unmap((ptr_t)next, nextsize);
 423               } else {
 424                 GC_remap((ptr_t)h, size);
 425                 hhdr -> hb_flags &= ~WAS_UNMAPPED;
 426                 hhdr -> hb_last_reclaimed = nexthdr -> hb_last_reclaimed;
 427               }
 428             } else {
 429               /* Unmap any gap in the middle */
 430                 GC_unmap_gap((ptr_t)h, size, (ptr_t)next, nexthdr -> hb_sz);
 431             }
 432             /* If they are both unmapped, we merge, but leave unmapped. */
 433             GC_remove_from_fl(hhdr, i);
 434             GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 435             hhdr -> hb_sz += nexthdr -> hb_sz;
 436             GC_remove_header(next);
 437             GC_add_to_fl(h, hhdr);
 438             /* Start over at beginning of list */
 439             h = GC_hblkfreelist[i];
 440           } else /* not mergable with successor */ {
 441             h = hhdr -> hb_next;
 442           }
 443       } /* while (h != 0) ... */
 444     } /* for ... */
 445 }
 446
 447 #endif /* USE_MUNMAP */
 448
 449 /*
 450  * Return a pointer to a block starting at h of length bytes.
 451  * Memory for the block is mapped.
 452  * Remove the block from its free list, and return the remainder (if any)
 453  * to its appropriate free list.
 454  * May fail by returning 0.
 455  * The header for the returned block must be set up by the caller.
 456  * If the return value is not 0, then hhdr is the header for it.
 457  */
 458 struct hblk * GC_get_first_part(h, hhdr, bytes, index)
 459 struct hblk *h;
 460 hdr * hhdr;
 461 word bytes;
 462 int index;
 463 {
 464     word total_size = hhdr -> hb_sz;
 465     struct hblk * rest;
 466     hdr * rest_hdr;
 467
 468     GC_ASSERT((total_size & (HBLKSIZE-1)) == 0);
 469     GC_remove_from_fl(hhdr, index);
 470     if (total_size == bytes) return h;
 471     rest = (struct hblk *)((word)h + bytes);
 472     rest_hdr = GC_install_header(rest);
 473     if (0 == rest_hdr) {
 474         /* This may be very bad news ... */
 475         WARN("Header allocation failed: Dropping block.\n", 0);
 476         return(0);
 477     }
 478     rest_hdr -> hb_sz = total_size - bytes;
 479     rest_hdr -> hb_flags = 0;
 480 #   ifdef GC_ASSERTIONS
 481       /* Mark h not free, to avoid assertion about adjacent free blocks. */
 482         hhdr -> hb_map = 0;
 483 #   endif
 484     GC_add_to_fl(rest, rest_hdr);
 485     return h;
 486 }
 487
 488 /*
 489  * H is a free block.  N points at an address inside it.
 490  * A new header for n has already been set up.  Fix up h's header
 491  * to reflect the fact that it is being split, move it to the
 492  * appropriate free list.
 493  * N replaces h in the original free list.
 494  *
 495  * Nhdr is not completely filled in, since it is about to allocated.
 496  * It may in fact end up on the wrong free list for its size.
 497  * (Hence adding it to a free list is silly.  But this path is hopefully
 498  * rare enough that it doesn't matter.  The code is cleaner this way.)
 499  */
 500 void GC_split_block(h, hhdr, n, nhdr, index)
 501 struct hblk *h;
 502 hdr * hhdr;
 503 struct hblk *n;
 504 hdr * nhdr;
 505 int index;      /* Index of free list */
 506 {
 507     word total_size = hhdr -> hb_sz;
 508     word h_size = (word)n - (word)h;
 509     struct hblk *prev = hhdr -> hb_prev;
 510     struct hblk *next = hhdr -> hb_next;
 511
 512     /* Replace h with n on its freelist */
 513       nhdr -> hb_prev = prev;
 514       nhdr -> hb_next = next;
 515       nhdr -> hb_sz = total_size - h_size;
 516       nhdr -> hb_flags = 0;
 517       if (0 != prev) {
 518         HDR(prev) -> hb_next = n;
 519       } else {
 520         GC_hblkfreelist[index] = n;
 521       }
 522       if (0 != next) {
 523         HDR(next) -> hb_prev = n;
 524       }
 525       INCR_FREE_BYTES(index, -(signed_word)h_size);
 526       FREE_ASSERT(GC_free_bytes[index] > 0);
 527 #     ifdef GC_ASSERTIONS
 528         nhdr -> hb_map = 0;     /* Don't fail test for consecutive      */
 529                                 /* free blocks in GC_add_to_fl.         */
 530 #     endif
 531 #   ifdef USE_MUNMAP
 532       hhdr -> hb_last_reclaimed = GC_gc_no;
 533 #   endif
 534     hhdr -> hb_sz = h_size;
 535     GC_add_to_fl(h, hhdr);
 536     GC_invalidate_map(nhdr);
 537 }
 538
 539 struct hblk * GC_allochblk_nth();
 540
 541 /*
 542  * Allocate (and return pointer to) a heap block
 543  *   for objects of size sz words, searching the nth free list.
 544  *
 545  * NOTE: We set obj_map field in header correctly.
 546  *       Caller is responsible for building an object freelist in block.
 547  *
 548  * Unlike older versions of the collectors, the client is responsible
 549  * for clearing the block, if necessary.
 550  */
 551 struct hblk *
 552 GC_allochblk(sz, kind, flags)
 553 word sz;
 554 int kind;
 555 unsigned flags;  /* IGNORE_OFF_PAGE or 0 */
 556 {
 557     word blocks = OBJ_SZ_TO_BLOCKS(sz);
 558     int start_list = GC_hblk_fl_from_blocks(blocks);
 559     int i;
 560     for (i = start_list; i <= N_HBLK_FLS; ++i) {
 561         struct hblk * result = GC_allochblk_nth(sz, kind, flags, i);
 562         if (0 != result) {
 563             return result;
 564         }
 565     }
 566     return 0;
 567 }
 568 /*
 569  * The same, but with search restricted to nth free list.
 570  */
 571 struct hblk *
 572 GC_allochblk_nth(sz, kind, flags, n)
 573 word sz;
 574 int kind;
 575 unsigned char flags;  /* IGNORE_OFF_PAGE or 0 */
 576 int n;
 577 {
 578     register struct hblk *hbp;
 579     register hdr * hhdr;                /* Header corr. to hbp */
 580     register struct hblk *thishbp;
 581     register hdr * thishdr;             /* Header corr. to hbp */
 582     signed_word size_needed;    /* number of bytes in requested objects */
 583     signed_word size_avail;     /* bytes available in this block        */
 584
 585     size_needed = HBLKSIZE * OBJ_SZ_TO_BLOCKS(sz);
 586
 587     /* search for a big enough block in free list */
 588         hbp = GC_hblkfreelist[n];
 589         for(; 0 != hbp; hbp = hhdr -> hb_next) {
 590             GET_HDR(hbp, hhdr);
 591             size_avail = hhdr->hb_sz;
 592             if (size_avail < size_needed) continue;
 593             if (size_avail != size_needed
 594                 && !GC_use_entire_heap
 595                 && !GC_dont_gc
 596                 && USED_HEAP_SIZE >= GC_requested_heapsize
 597                 && !TRUE_INCREMENTAL && GC_should_collect()) {
 598 #               ifdef USE_MUNMAP
 599                     continue;
 600 #               else
 601                     /* If we have enough large blocks left to cover any */
 602                     /* previous request for large blocks, we go ahead   */
 603                     /* and split.  Assuming a steady state, that should */
 604                     /* be safe.  It means that we can use the full      */
 605                     /* heap if we allocate only small objects.          */
 606                     if (!GC_enough_large_bytes_left(GC_large_allocd_bytes, n)) {
 607                       continue;
 608                     }
 609                     /* If we are deallocating lots of memory from       */
 610                     /* finalizers, fail and collect sooner rather       */
 611                     /* than later.                                      */
 612                     if (WORDS_TO_BYTES(GC_finalizer_mem_freed)
 613                         > (GC_heapsize >> 4))  {
 614                       continue;
 615                     }
 616 #               endif /* !USE_MUNMAP */
 617             }
 618             /* If the next heap block is obviously better, go on.       */
 619             /* This prevents us from disassembling a single large block */
 620             /* to get tiny blocks.                                      */
 621             {
 622               signed_word next_size;
 623
 624               thishbp = hhdr -> hb_next;
 625               if (thishbp != 0) {
 626                 GET_HDR(thishbp, thishdr);
 627                 next_size = (signed_word)(thishdr -> hb_sz);
 628                 if (next_size < size_avail
 629                   && next_size >= size_needed
 630                   && !GC_is_black_listed(thishbp, (word)size_needed)) {
 631                   continue;
 632                 }
 633               }
 634             }
 635             if ( !IS_UNCOLLECTABLE(kind) &&
 636                  (kind != PTRFREE || size_needed > MAX_BLACK_LIST_ALLOC)) {
 637               struct hblk * lasthbp = hbp;
 638               ptr_t search_end = (ptr_t)hbp + size_avail - size_needed;
 639               signed_word orig_avail = size_avail;
 640               signed_word eff_size_needed = ((flags & IGNORE_OFF_PAGE)?
 641                                                 HBLKSIZE
 642                                                 : size_needed);
 643
 644
 645               while ((ptr_t)lasthbp <= search_end
 646                      && (thishbp = GC_is_black_listed(lasthbp,
 647                                                       (word)eff_size_needed))
 648                         != 0) {
 649                 lasthbp = thishbp;
 650               }
 651               size_avail -= (ptr_t)lasthbp - (ptr_t)hbp;
 652               thishbp = lasthbp;
 653               if (size_avail >= size_needed) {
 654                 if (thishbp != hbp &&
 655                     0 != (thishdr = GC_install_header(thishbp))) {
 656                   /* Make sure it's mapped before we mangle it. */
 657 #                   ifdef USE_MUNMAP
 658                       if (!IS_MAPPED(hhdr)) {
 659                         GC_remap((ptr_t)hbp, hhdr -> hb_sz);
 660                         hhdr -> hb_flags &= ~WAS_UNMAPPED;
 661                       }
 662 #                   endif
 663                   /* Split the block at thishbp */
 664                       GC_split_block(hbp, hhdr, thishbp, thishdr, n);
 665                   /* Advance to thishbp */
 666                       hbp = thishbp;
 667                       hhdr = thishdr;
 668                       /* We must now allocate thishbp, since it may     */
 669                       /* be on the wrong free list.                     */
 670                 }
 671               } else if (size_needed > (signed_word)BL_LIMIT
 672                          && orig_avail - size_needed
 673                             > (signed_word)BL_LIMIT) {
 674                 /* Punt, since anything else risks unreasonable heap growth. */
 675                 if (++GC_large_alloc_warn_suppressed
 676                     >= GC_large_alloc_warn_interval) {
 677                   WARN("Repeated allocation of very large block "
 678                        "(appr. size %ld):\n"
 679                        "\tMay lead to memory leak and poor performance.\n",
 680                        size_needed);
 681                   GC_large_alloc_warn_suppressed = 0;
 682                 }
 683                 size_avail = orig_avail;
 684               } else if (size_avail == 0 && size_needed == HBLKSIZE
 685                          && IS_MAPPED(hhdr)) {
 686                 if (!GC_find_leak) {
 687                   static unsigned count = 0;
 688
 689                   /* The block is completely blacklisted.  We need      */
 690                   /* to drop some such blocks, since otherwise we spend */
 691                   /* all our time traversing them if pointerfree        */
 692                   /* blocks are unpopular.                              */
 693                   /* A dropped block will be reconsidered at next GC.   */
 694                   if ((++count & 3) == 0) {
 695                     /* Allocate and drop the block in small chunks, to  */
 696                     /* maximize the chance that we will recover some    */
 697                     /* later.                                           */
 698                       word total_size = hhdr -> hb_sz;
 699                       struct hblk * limit = hbp + divHBLKSZ(total_size);
 700                       struct hblk * h;
 701                       struct hblk * prev = hhdr -> hb_prev;
 702
 703                       GC_words_wasted += BYTES_TO_WORDS(total_size);
 704                       GC_large_free_bytes -= total_size;
 705                       GC_remove_from_fl(hhdr, n);
 706                       for (h = hbp; h < limit; h++) {
 707                         if (h == hbp || 0 != (hhdr = GC_install_header(h))) {
 708                           (void) setup_header(
 709                                   hhdr,
 710                                   BYTES_TO_WORDS(HBLKSIZE),
 711                                   PTRFREE, 0); /* Cant fail */
 712                           if (GC_debugging_started) {
 713                             BZERO(h, HBLKSIZE);
 714                           }
 715                         }
 716                       }
 717                     /* Restore hbp to point at free block */
 718                       hbp = prev;
 719                       if (0 == hbp) {
 720                         return GC_allochblk_nth(sz, kind, flags, n);
 721                       }
 722                       hhdr = HDR(hbp);
 723                   }
 724                 }
 725               }
 726             }
 727             if( size_avail >= size_needed ) {
 728 #               ifdef USE_MUNMAP
 729                   if (!IS_MAPPED(hhdr)) {
 730                     GC_remap((ptr_t)hbp, hhdr -> hb_sz);
 731                     hhdr -> hb_flags &= ~WAS_UNMAPPED;
 732                   }
 733 #               endif
 734                 /* hbp may be on the wrong freelist; the parameter n    */
 735                 /* is important.                                        */
 736                 hbp = GC_get_first_part(hbp, hhdr, size_needed, n);
 737                 break;
 738             }
 739         }
 740
 741     if (0 == hbp) return 0;
 742
 743     /* Add it to map of valid blocks */
 744         if (!GC_install_counts(hbp, (word)size_needed)) return(0);
 745         /* This leaks memory under very rare conditions. */
 746
 747     /* Set up header */
 748         if (!setup_header(hhdr, sz, kind, flags)) {
 749             GC_remove_counts(hbp, (word)size_needed);
 750             return(0); /* ditto */
 751         }
 752
 753     /* Notify virtual dirty bit implementation that we are about to write.  */
 754     /* Ensure that pointerfree objects are not protected if it's avoidable. */
 755         GC_remove_protection(hbp, divHBLKSZ(size_needed),
 756                              (hhdr -> hb_descr == 0) /* pointer-free */);
 757
 758     /* We just successfully allocated a block.  Restart count of        */
 759     /* consecutive failures.                                            */
 760     {
 761         extern unsigned GC_fail_count;
 762
 763         GC_fail_count = 0;
 764     }
 765
 766     GC_large_free_bytes -= size_needed;
 767
 768     GC_ASSERT(IS_MAPPED(hhdr));
 769     return( hbp );
 770 }
 771
 772 struct hblk * GC_freehblk_ptr = 0;  /* Search position hint for GC_freehblk */
 773
 774 /*
 775  * Free a heap block.
 776  *
 777  * Coalesce the block with its neighbors if possible.
 778  *
 779  * All mark words are assumed to be cleared.
 780  */
 781 void
 782 GC_freehblk(hbp)
 783 struct hblk *hbp;
 784 {
 785 struct hblk *next, *prev;
 786 hdr *hhdr, *prevhdr, *nexthdr;
 787 signed_word size;
 788
 789
 790     GET_HDR(hbp, hhdr);
 791     size = hhdr->hb_sz;
 792     size = HBLKSIZE * OBJ_SZ_TO_BLOCKS(size);
 793     GC_remove_counts(hbp, (word)size);
 794     hhdr->hb_sz = size;
 795 #   ifdef USE_MUNMAP
 796       hhdr -> hb_last_reclaimed = GC_gc_no;
 797 #   endif
 798
 799     /* Check for duplicate deallocation in the easy case */
 800       if (HBLK_IS_FREE(hhdr)) {
 801         GC_printf1("Duplicate large block deallocation of 0x%lx\n",
 802                    (unsigned long) hbp);
 803         ABORT("Duplicate large block deallocation");
 804       }
 805
 806     GC_ASSERT(IS_MAPPED(hhdr));
 807     GC_invalidate_map(hhdr);
 808     next = (struct hblk *)((word)hbp + size);
 809     GET_HDR(next, nexthdr);
 810     prev = GC_free_block_ending_at(hbp);
 811     /* Coalesce with successor, if possible */
 812       if(0 != nexthdr && HBLK_IS_FREE(nexthdr) && IS_MAPPED(nexthdr)) {
 813         GC_remove_from_fl(nexthdr, FL_UNKNOWN);
 814         hhdr -> hb_sz += nexthdr -> hb_sz;
 815         GC_remove_header(next);
 816       }
 817     /* Coalesce with predecessor, if possible. */
 818       if (0 != prev) {
 819         prevhdr = HDR(prev);
 820         if (IS_MAPPED(prevhdr)) {
 821           GC_remove_from_fl(prevhdr, FL_UNKNOWN);
 822           prevhdr -> hb_sz += hhdr -> hb_sz;
 823 #         ifdef USE_MUNMAP
 824             prevhdr -> hb_last_reclaimed = GC_gc_no;
 825 #         endif
 826           GC_remove_header(hbp);
 827           hbp = prev;
 828           hhdr = prevhdr;
 829         }
 830       }
 831     /* FIXME: It is not clear we really always want to do these merges  */
 832     /* with -DUSE_MUNMAP, since it updates ages and hence prevents      */
 833     /* unmapping.                                                       */
 834
 835     GC_large_free_bytes += size;
 836     GC_add_to_fl(hbp, hhdr);
 837 }
 838