/*
 * Generational Conservative Garbage Collector for CMUCL x86.
 *
 * This code was written by Douglas T. Crosher, based on Public Domain
 * codes from Carnegie Mellon University. This code has been placed in
 * the public domain, and is provided 'as is'.
 *
 * Douglas Crosher, 1996, 1997.
 *
 * $Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/lisp/gencgc.c,v 1.1 1997/11/25 17:59:18 dtc Exp $
 * */

#include <stdio.h>
#include <signal.h>
#include "lisp.h"
#include "internals.h"
#include "os.h"
#include "globals.h"
#include "interrupt.h"
#include "validate.h"
#include "lispregs.h"

#include "gencgc.h"

#define gc_abort() lose("GC invariant lost!  File \"%s\", line %d\n", \
			__FILE__, __LINE__)

#if 1
#define gc_assert(ex) do { \
	if (!(ex)) gc_abort(); \
} while (0)
#else
#define gc_assert(ex)
#endif


/* The number of generations, an extra is added to this for use as a
   temp. */
#define NUM_GENERATIONS 6

/* Debugging variables. */

boolean gencgc_verbose = FALSE;

/* To enable the use of page protection to help avoid the scavenging
   of pages that don't have pointers to younger generations. */
boolean  enable_page_protection = TRUE;

/* Hunt for pointers to old-space, when GCing generations >=
   verify_gen. Set to NUM_GENERATIONS to disable. */
int verify_gens = NUM_GENERATIONS-1;

/* Enable a pre-scan verify of generation 0 before it's GCed */
boolean pre_verify_gen_0 = FALSE;

/* Enable the printing of a note when code objects are found in the
   dynamic space during a heap verify. */
boolean verify_dynamic_code_check = FALSE;

/* Enable the checking of code objects for fixup errors after they are
   transported. */
boolean check_code_fixups = TRUE;

/* To enable unmapping of a page and re-mmaping it to have it zero
   filled. */
#if defined(__FreeBSD__)
/* Note: this can waste a lot of swap on FreeBSD so don't unmap. */
boolean gencgc_unmap_zero = FALSE;
#else
boolean gencgc_unmap_zero = TRUE;
#endif

/* Enable checking that newly allocated regions are zero filled. */
boolean gencgc_zero_check = FALSE;

/* The minimum size for a large object. */
unsigned large_object_size = 4*4096;

/* Enable the filtering of stack/register pointers. This could reduce
   the number of invalid pointers accepted. It will probably degrades
   interrupt safety during object initialisation. */
boolean enable_pointer_filter = TRUE;


/* The total bytes allocated. Seen by (dynamic-usage) */
unsigned long bytes_allocated = 0;
static unsigned long auto_gc_trigger = 0;

/* The src. and dest. generations. Set before a GC starts scavenging */
static int from_space;
static int new_space;


/* GC structures and variables.*/

#define PAGE_BYTES 4096

/* An array of page structures is statically allocated.
   This helps quickly map between an address its page structure.
   NUM_PAGES is set from the size of the dynamic space. */
struct page page_table[NUM_PAGES];

/* To map addresses to page structures the address of the first page
   is needed. */
static void *heap_base = NULL;

/* Calculate the start address for the given page number. */
inline void
*page_address(int page_num)
{
  return (heap_base + (page_num * 4096));
}

/* Find the page index within the page_table for the given
   address. Returns -1 on failure. */
inline int
find_page_index(void *addr)
{
  int index = addr-heap_base;

  if (index >= 0) {
    index = ((unsigned int)index)/4096;
    if (index < NUM_PAGES)
      return (index);
  }

  return (-1);
}


/* A structure to hold the state of a generation */
struct generation {

  /* The first page that gc_alloc checks on its next call. */
  int  alloc_start_page;

  /* The first page that gc_alloc_unboxed checks on its next call. */
  int  alloc_unboxed_start_page;

  /* The first page that gc_alloc_large (boxed) considers on its next
     call. Although it always allocates after the boxed_region. */
  int  alloc_large_start_page;

  /* The first page that gc_alloc_large (unboxed) considers on its
     next call. Although it always allocates after the
     current_unboxed_region. */
  int  alloc_large_unboxed_start_page;

  /* The bytes allocate to this generation. */
  int  bytes_allocated;

  /* The number of bytes at which to trigger a GC */
  int  gc_trigger;

  /* To calculate a new level for gc_trigger */
  int  bytes_consed_between_gc;

  /* The number of GCs since the last raise. */
  int  num_gc;

  /* The average age at after which a GC will raise objects to the
     next generation. */
  int  trigger_age;

  /* The cumulative sum of the bytes allocated to this generation. It is
     cleared after a GC on this generations, and update before new
     objects are added from a GC of a younger generation. Dividing by
     the bytes_allocated will give the average age of the memory in
     this generation since its last GC. */
  int  cum_sum_bytes_allocated;

  /* A minimum average memory age before a GC will occur helps
     prevent a GC when a large number of new live objects have been
     added, in which case a GC could be a waste of time. */
  double  min_av_mem_age;
};

/* An array of generation structures. There needs to be one more
   generation structure than actual generations as the oldest
   generations is temporarily raised then lowered. */
static struct generation generations[NUM_GENERATIONS+1];

/* The oldest generation that is will currently be GCed by default.
   Valid values are: 0, 1, ... (NUM_GENERATIONS-1)

   The default of (NUM_GENERATIONS-1) enables GC on all generations.

   Setting this to 0 effectively disables the generational nature of
   the GC. In some applications generational GC may not be useful
   because there are no long-lived objects.

   An intermediate value could be handy after moving long-lived data
   into an older generation so an unnecessary GC of this long-lived
   data can be avoided. */
unsigned int  gencgc_oldest_gen_to_gc = NUM_GENERATIONS-1;


/* The maximum free page in the heap is maintained and used to update
   ALLOCATION_POINTER which is used by the room function
   to limit its search of the heap. XX Gencgc obviously needs to be
   better integrated with the lisp code. */
static int  last_free_page;
static int  last_used_page = 0;



/* Misc. heap functions. */

/* Count the number of pages write protected within the given
   generation */
static int
count_write_protect_generation_pages(int generation)
{
  int i;
  int cnt = 0;
  
  for (i = 0; i < last_free_page; i++)
    if ((page_table[i].allocated != FREE_PAGE)
	&& (page_table[i].gen == generation)
	&& (page_table[i].write_protected == 1))
      cnt++;
  return(cnt);
}

/* Count the number of pages within the given generation */
static int
count_generation_pages(int generation)
{
  int i;
  int cnt = 0;
  
  for (i = 0; i < last_free_page; i++)
    if ((page_table[i].allocated != 0)
	&& (page_table[i].gen == generation))
      cnt++;
  return(cnt);
}

/* Count the number of dont_move pages. */
static int
count_dont_move_pages(void)
{
  int i;
  int cnt = 0;
  
  for (i = 0; i < last_free_page; i++)
    if ((page_table[i].allocated != 0)
	&& (page_table[i].dont_move != 0))
      cnt++;
  return(cnt);
}

/* Work through the pages and add up the number of bytes used for the
   given generation. */
static int
generation_bytes_allocated (int gen)
{
  int i;
  int bytes_allocated = 0;
  
  for (i = 0; i < last_free_page; i++) {
    if ((page_table[i].allocated != 0) && (page_table[i].gen == gen))
      bytes_allocated += page_table[i].bytes_used;
  }
  return (bytes_allocated);
}

/* Return the average age of the memory in a generation. */
static double
gen_av_mem_age(int gen)
{
  if (generations[gen].bytes_allocated == 0)
    return (0.0);
  
  return (((double)generations[gen].cum_sum_bytes_allocated)/((double)generations[gen].bytes_allocated));
}

/* The verbose argument controls how much to print out: 0 for normal
   level of detail; 1 for debugging. */
static void
print_generation_stats(int  verbose)
{
  int i, gens;

  /* Number of generations to print out. */
  if (verbose)
    gens = NUM_GENERATIONS+1;
  else
    gens = NUM_GENERATIONS;

  /* Print the heap stats */
  fprintf(stderr,"   Generation Boxed Unboxed LB   LUB    Alloc  Waste   Trig    WP  GCs Mem-age\n");

  for (i = 0; i < gens; i++) {
    int j;
    int boxed_cnt = 0;
    int unboxed_cnt = 0;
    int large_boxed_cnt = 0;
    int large_unboxed_cnt = 0;
    
    for (j = 0; j < last_free_page; j++)
      if (page_table[j].gen == i) {
	/* Count the number of boxed pages within the given generation */
	if (page_table[j].allocated == BOXED_PAGE)
	  if (page_table[j].large_object)
	    large_boxed_cnt++;
	  else
	    boxed_cnt++;
	
	/* Count the number of unboxed pages within the given generation */
	if (page_table[j].allocated == UNBOXED_PAGE)
	  if (page_table[j].large_object)
	    large_unboxed_cnt++;
	  else
	    unboxed_cnt++;
      }
    
    gc_assert(generations[i].bytes_allocated == generation_bytes_allocated(i));
    fprintf(stderr,"   %8d: %5d %5d %5d %5d %8d %5d %8d %4d %3d %7.4lf\n",
	    i,
	    boxed_cnt, unboxed_cnt, large_boxed_cnt, large_unboxed_cnt,
	    generations[i].bytes_allocated,
	    (count_generation_pages(i)*4096 - generations[i].bytes_allocated),
	    generations[i].gc_trigger,
	    count_write_protect_generation_pages(i),
	    generations[i].num_gc,
	    gen_av_mem_age(i));
  }
  fprintf(stderr,"   Total bytes alloc=%d\n", bytes_allocated);
}



/* Allocation routines */

/* To support quick and inline allocation, regions of memory can be
   allocated and then allocated from with just a free pointer and a
   check against an end address.

   Since objects can be allocated to spaces with different properties
   e.g. boxed/unboxed, generation, ages; there may need to be many
   allocation regions.

   Each allocation region may be start within a partly used page.
   Many features of memory use are noted on a page wise basis,
   E.g. the generation; so if a region starts within an existing
   allocated page it must be consistent with this page.

   During the scavenging of the newspace, objects will be transported
   into an allocation region, and pointers updated to point to this
   allocation region. It is possible that these pointers will be
   scavenged again before the allocation region is closed, E.g. due to
   trans_list which jumps all over the place to cleanup the list. It
   is important to be able to determine properties of all objects
   pointed to when scavenging, E.g to detect pointers to the
   oldspace. Thus it's important that the allocation regions have the
   correct properties set when allocated, and not just set when
   closed.  The region allocation routines return regions with the
   specified properties, and grab all the pages, setting there
   properties appropriately, except that the amount used is not known.

   These regions are used to support quicker allocation using just a
   free pointer. The actual space used by the region is not reflected
   in the pages tables until it is closed. It can't be scavenged until
   closed.

   When finished with the region it should be closed, which will
   update the page tables for the actual space used returning unused
   space. Further it may be noted in the new regions which is
   necessary when scavenging the newspace.

   Large objects may be allocated directly without an allocation
   region, the page tables are updated immediately.

   Unboxed objects don't contain points to other objects so don't need
   scavenging. Further they can't contain pointers to younger
   generations so WP is not needed.  By allocating pages to unboxed
   objects the whole page never needs scavenging or write protecting.

   */

/* Only using two regions at present, both are for the current
   newspace generation. */
struct alloc_region  boxed_region;
struct alloc_region  unboxed_region;

/* X hack. current lisp code uses the following. Need coping
   in/out. */
void *current_region_free_pointer;
void *current_region_end_addr;

/* The generation currently being allocated to. X */
static int  gc_alloc_generation;

/* Find a new region with room for at least the given number of bytes.

   It starts looking at the current generations alloc_start_page. So
   may pick up from the previous region if there is enough space. This
   keeps the allocation contiguous when scavenging the newspace.

   The alloc_region is should have been closed by a call to
   gc_alloc_update_page_tables, and will thus be in an empty state.
   
   To assist the scavenging functions write protected pages are not
   used. Free pages should not be write protected.

   It is critical to the conservative GC that the start of regions be
   known. To help achieve this only small regions are allocated at a
   time.

   During scavenging pointers may be found to within the current
   region and the page generation must be set so pointers to the from
   space can be recognised.  So the generation of pages in the region
   are set to gc_alloc_generation.  To prevent another allocation call
   using the same pages, all the pages in the region are allocated,
   although they will initially be empty.

  */
static void
gc_alloc_new_region(int nbytes, int unboxed, struct alloc_region *alloc_region)
{
  int first_page;
  int last_page;
  int region_size;
  int restart_page;
  int bytes_found;
  int num_pages;
  int i;

  /* fprintf(stderr,"alloc_new_region for %d bytes from gen %d\n",
	  nbytes, gc_alloc_generation);*/

  /* Check that the region is in a reset state. */
  gc_assert((alloc_region->first_page == 0)
	    && (alloc_region->last_page == -1)
	    && (alloc_region->free_pointer == alloc_region->end_addr));

  if (unboxed)
    restart_page = generations[gc_alloc_generation].alloc_unboxed_start_page;
  else
    restart_page = generations[gc_alloc_generation].alloc_start_page;

  /* Search for a contiguous free region of at least nbytes with the
     given properties: boxed/unboxed, generation. */
  do {
    first_page = restart_page;
    
    /* First search for a page with at least 32 bytes free, that is
       not write protected, or marked dont_move. */
    while ((first_page < NUM_PAGES)
	   && (page_table[first_page].allocated != FREE_PAGE) /* Not free page */
	   && ((unboxed && (page_table[first_page].allocated != UNBOXED_PAGE))
	       || (!unboxed &&
		   (page_table[first_page].allocated != BOXED_PAGE))
	       || (page_table[first_page].large_object != 0)
	       || (page_table[first_page].gen != gc_alloc_generation)
	       || (page_table[first_page].bytes_used >= (4096-32))
	       || (page_table[first_page].write_protected != 0)
	       || (page_table[first_page].dont_move != 0)))
      first_page++;
    /* Check for a failure */
    if (first_page >= NUM_PAGES) {
      fprintf(stderr,"*A2 gc_alloc_new_region failed, nbytes=%d.\n", nbytes);
      print_generation_stats(1);
      exit(1);
    }
    
    gc_assert(page_table[first_page].write_protected == 0);
    
    /*      fprintf(stderr,"  first_page=%d bytes_used=%d\n",first_page, page_table[first_page].bytes_used);*/
    
    /* Now search forward to calculate the available region size.  It
       tries to keeps going until nbytes are found and the number of
       pages is greater than some level. This helps keep down the
       number of pages in a region. */
    last_page = first_page;
    bytes_found = 4096 - page_table[first_page].bytes_used;
    num_pages = 1;
    while (((bytes_found < nbytes) || (num_pages < 2))
	   && (last_page < (NUM_PAGES-1))
	   && (page_table[last_page+1].allocated == FREE_PAGE)) {
      last_page++;
      num_pages++;
      bytes_found += 4096;
      gc_assert(page_table[last_page].write_protected == 0);
    }
    
    region_size = (4096 - page_table[first_page].bytes_used)
      + 4096*(last_page-first_page);
    
    gc_assert(bytes_found == region_size);
    
    /* fprintf(stderr,"  last_page=%d bytes_found=%d num_pages=%d\n",last_page, bytes_found, num_pages);*/
    
    restart_page = last_page + 1;
  }
  while ((restart_page < NUM_PAGES) && (bytes_found < nbytes));
  
  /* Check for a failure */
  if ((restart_page >= NUM_PAGES) && (bytes_found < nbytes)) {
    fprintf(stderr,"*A1 gc_alloc_new_region failed, nbytes=%d.\n", nbytes);
    print_generation_stats(1);
    exit(1);
  }
  
  /*fprintf(stderr,"gc_alloc_new_region gen %d: %d bytes: from pages %d to %d: addr=%x\n", gc_alloc_generation, bytes_found, first_page, last_page, page_address(first_page));*/
  
  /* Setup the alloc_region. */
  alloc_region->first_page = first_page;
  alloc_region->last_page = last_page;
  alloc_region->start_addr = page_table[first_page].bytes_used
    + page_address(first_page);
  alloc_region->free_pointer = alloc_region->start_addr;
  alloc_region->end_addr = alloc_region->start_addr + bytes_found;

  if (gencgc_zero_check) {
    int *p;
    for(p = (int *)alloc_region->start_addr;
	p < (int *)alloc_region->end_addr; p++)
      if (*p != 0)
	fprintf(stderr,"** new region not zero @ %x\n",p);
  }

  /* Setup the pages. */

  /* The first page may have already been in use. */
  if (page_table[first_page].bytes_used == 0) {
    if (unboxed)
      page_table[first_page].allocated = UNBOXED_PAGE;
    else
      page_table[first_page].allocated = BOXED_PAGE;
    page_table[first_page].gen = gc_alloc_generation;
    page_table[first_page].large_object = 0;
    page_table[first_page].first_object_offset = 0;
  }
  
  if (unboxed)
    gc_assert(page_table[first_page].allocated == UNBOXED_PAGE);
  else
    gc_assert(page_table[first_page].allocated == BOXED_PAGE);
  gc_assert(page_table[first_page].gen == gc_alloc_generation);
  gc_assert(page_table[first_page].large_object == 0);

  for (i = first_page+1; i <= last_page; i++) {
    if (unboxed)
      page_table[i].allocated = UNBOXED_PAGE;
    else
      page_table[i].allocated = BOXED_PAGE;
    page_table[i].gen = gc_alloc_generation;
    page_table[i].large_object = 0;
    /* This may not be necessary for unboxed regions (think it was
       broken before!) */
    page_table[i].first_object_offset =
      alloc_region->start_addr - page_address(i);
  }

  /* Bump up last_free_page */
  if (last_page+1 > last_free_page) {
    last_free_page = last_page+1;
    SetSymbolValue(ALLOCATION_POINTER,
		   (lispobj)(((char *)heap_base) + last_free_page*4096));
    if (last_page+1 > last_used_page)
      last_used_page = last_page+1;
  }
}



/* If the record_new_objects flag is 2 then all new regions created
   are recorded.

   If it's 1 then then it is only recorded if the first page of the
   current region is <= new_areas_ignore_page. This helps avoid
   unnecessary recording when doing full scavenge pass.

   The new_object structure holds the page, byte offset, and size of
   new regions of objects. Each new area is placed in the array of
   these structures pointer to by new_areas. new_areas_index holds the
   offset into new_areas.

   If new_area overflows NUM_NEW_AREAS then it stops adding them. The
   later code must detect this an handle it, probably by doing a full
   scavenge of a generation.  */

#define NUM_NEW_AREAS 512
static int record_new_objects = 0;
static int new_areas_ignore_page;
struct new_area {
  int  page;
  int  offset;
  int  size;
};
static struct new_area (*new_areas)[];
static new_areas_index;
int max_new_areas;

/* Add a new area to new_areas. */
static void
add_new_area(int first_page, int offset, int size)
{
  unsigned new_area_start,c;
  int i;

  /* Ignore if full */
  if (new_areas_index >= NUM_NEW_AREAS)
    return;

  switch (record_new_objects) {
  case 0:
    return;
  case 1:
    if (first_page > new_areas_ignore_page)
      return;
    break;
  case 2:
    break;
  default:
    gc_abort();
  }
  
  new_area_start = 4096*first_page + offset;

  /* Search backwards for a prior area that this follows from.  If
     found this will save adding a new area. */
  for (i = new_areas_index-1, c = 0; (i >= 0) && (c < 8); i--, c++) {
    unsigned area_end = 4096*((*new_areas)[i].page)
      + (*new_areas)[i].offset + (*new_areas)[i].size; 
    /*fprintf(stderr,"*S1 %d %d %d %d\n",i,c,new_area_start,area_end);*/
    if (new_area_start == area_end) {
      /*fprintf(stderr,"-> Adding to [%d] %d %d %d with %d %d %d:\n",
	      i, (*new_areas)[i].page, (*new_areas)[i].offset ,
	      (*new_areas)[i].size, first_page, offset, size);*/
      (*new_areas)[i].size += size;
      return;
    }
  }
  /*fprintf(stderr,"*S1 %d %d %d\n",i,c,new_area_start);*/

  (*new_areas)[new_areas_index].page = first_page;
  (*new_areas)[new_areas_index].offset = offset;
  (*new_areas)[new_areas_index].size = size;
  /*fprintf(stderr,"  new_area %d page %d offset %d size %d\n",
	  new_areas_index, first_page, offset, size);*/
  new_areas_index++;
  
  /* Note the max new_areas used. */
  if (new_areas_index > max_new_areas)
    max_new_areas = new_areas_index;
}


/* Update the tables for the alloc_region. The region maybe added to
   the new_areas.

   When done the alloc_region its setup so that the next quick alloc
   will fail safely and thus a new regions will be allocated. Further
   it is safe to try and re-update the page table of this reset
   alloc_region.

   */
void
gc_alloc_update_page_tables(int unboxed, struct alloc_region *alloc_region)
{
  int more;
  int first_page;
  int next_page;
  int bytes_used;
  int orig_first_page_bytes_used;
  int region_size;
  int byte_cnt;

  /*fprintf(stderr,"gc_alloc_update_page_tables to gen %d: ",
	  gc_alloc_generation);*/

  first_page = alloc_region->first_page;

  /* Catch an unused alloc_region. */
  if ((first_page == 0) && (alloc_region->last_page == -1))
    return;

  next_page = first_page+1;

  /* Skip if no bytes were allocated */
  if (alloc_region->free_pointer != alloc_region->start_addr) {
    orig_first_page_bytes_used = page_table[first_page].bytes_used;
    
    gc_assert(alloc_region->start_addr == (page_address(first_page) + page_table[first_page].bytes_used));
    
    /* All the pages used need to be updated */
    
    /* Update the first page. */
    
    /*      fprintf(stderr,"0");*/
    
    /* If the page was free then setup the gen, and
       first_object_offset. */
    if (page_table[first_page].bytes_used == 0)
      gc_assert(page_table[first_page].first_object_offset == 0);
    
    if (unboxed)
      gc_assert(page_table[first_page].allocated == UNBOXED_PAGE);
    else
      gc_assert(page_table[first_page].allocated == BOXED_PAGE);
    gc_assert(page_table[first_page].gen == gc_alloc_generation);
    gc_assert(page_table[first_page].large_object == 0);
    
    byte_cnt = 0;
    
    /* Calc. the number of bytes used in this page. This is not always
       the number of new bytes, unless it was free. */
    more = 0;
    if ((bytes_used = (alloc_region->free_pointer - page_address(first_page)))>4096) {
      bytes_used = 4096;
      more = 1;
    }
    page_table[first_page].bytes_used = bytes_used;
    byte_cnt += bytes_used;
    
    
    /* All the rest of the pages should be free. Need to set their
       first_object_offset pointer to the start of the region, and set
       the bytes_used. */
    while (more) {
      /*	  	  fprintf(stderr,"+")*/
      if (unboxed)
	gc_assert(page_table[next_page].allocated == UNBOXED_PAGE);
      else
	gc_assert(page_table[next_page].allocated == BOXED_PAGE);
      gc_assert(page_table[next_page].bytes_used == 0);
      gc_assert(page_table[next_page].gen == gc_alloc_generation);
      gc_assert(page_table[next_page].large_object == 0);
      
      gc_assert(page_table[next_page].first_object_offset ==
		alloc_region->start_addr - page_address(next_page));
      
      /* Calc. the number of bytes used in this page. */
      more = 0;
      if ((bytes_used = (alloc_region->free_pointer
			 - page_address(next_page)))>4096) {
	bytes_used = 4096;
	more = 1;
      }
      page_table[next_page].bytes_used = bytes_used;
      byte_cnt += bytes_used;
      
      next_page++;
    }
    
    region_size = alloc_region->free_pointer - alloc_region->start_addr;
    bytes_allocated += region_size;
    generations[gc_alloc_generation].bytes_allocated += region_size;
    
    gc_assert((byte_cnt- orig_first_page_bytes_used) == region_size);
    
    /* Set the generations alloc restart page to the last page of
       the region. */
    if (unboxed)
      generations[gc_alloc_generation].alloc_unboxed_start_page =
	next_page-1;
    else
      generations[gc_alloc_generation].alloc_start_page = next_page-1;
    
    /* Add the region to the new_areas if requested. */
    if (!unboxed)
      add_new_area(first_page,orig_first_page_bytes_used, region_size);
    
    /*            fprintf(stderr,"  gc_alloc_update_page_tables update %d bytes to gen %d\n",region_size,gc_alloc_generation);*/
  }
  else
    /* No bytes allocated. Unallocate the first_page if there are 0
       bytes_used. */
    if (page_table[first_page].bytes_used == 0)
      page_table[first_page].allocated = FREE_PAGE;
  
  /* Unallocate any unused pages. */
  while (next_page <= alloc_region->last_page) {
    gc_assert(page_table[next_page].bytes_used == 0);
    page_table[next_page].allocated = FREE_PAGE;
    next_page++;
  }

  /* Reset the alloc_region. */
  alloc_region->first_page = 0;
  alloc_region->last_page = -1;
  alloc_region->start_addr = page_address(0);
  alloc_region->free_pointer = page_address(0);
  alloc_region->end_addr = page_address(0);

  /*    fprintf(stderr,"\n");*/
}



static inline void *gc_quick_alloc(int nbytes);

/* Allocate a possibly large object. */
static void
*gc_alloc_large(int  nbytes, int unboxed, struct alloc_region *alloc_region)
{
  int first_page;
  int last_page;
  int region_size;
  int restart_page;
  int bytes_found;
  int num_pages;
  int orig_first_page_bytes_used;
  int byte_cnt;
  int more;
  int bytes_used;
  int next_page;
  int large = (nbytes >= large_object_size);

  /*  if (nbytes > 200000)
    fprintf(stderr,"*** alloc_large %d\n",nbytes);*/

  /*  fprintf(stderr,"gc_alloc_large for %d bytes from gen %d\n",
	  nbytes, gc_alloc_generation);*/

  /* If the object is small, and there is room in the current region
     then allocation it in the current region. */
  if (!large
      && ((alloc_region->end_addr-alloc_region->free_pointer) >= nbytes))
    return gc_quick_alloc(nbytes);
  
  /* Search for a contiguous free region of at least nbytes. If it's a
     large object then align it on a page boundary by searching for a
     free page. */

  /* To allow the allocation of small objects without the danger of
     using a page in the current boxed region, the search starts after
     the current boxed free region. XX could probably keep a page
     index ahead of the current region and bumped up here to save a
     lot of re-scanning. */
  if (unboxed)
    restart_page = generations[gc_alloc_generation].alloc_large_unboxed_start_page;
  else
    restart_page = generations[gc_alloc_generation].alloc_large_start_page;
  if (restart_page <= alloc_region->last_page)
    restart_page = alloc_region->last_page+1;

  do {
    first_page = restart_page;
    
    if (large)
      while ((first_page < NUM_PAGES)
	     && (page_table[first_page].allocated != FREE_PAGE))
	first_page++;
    else
      while ((first_page < NUM_PAGES)
	     && (page_table[first_page].allocated != FREE_PAGE)
	     && ((unboxed &&
		  (page_table[first_page].allocated != UNBOXED_PAGE))
		 || (!unboxed &&
		     (page_table[first_page].allocated != BOXED_PAGE))
		 || (page_table[first_page].large_object != 0)
		 || (page_table[first_page].gen != gc_alloc_generation)
		 || (page_table[first_page].bytes_used >= (4096-32))
		 || (page_table[first_page].write_protected != 0)
		 || (page_table[first_page].dont_move != 0)))
	first_page++;
    
    /* Check for a failure */
    if (first_page >= NUM_PAGES) {
      fprintf(stderr,"*A2 gc_alloc_large failed, nbytes=%d.\n", nbytes);
      print_generation_stats(1);
      exit(1);
    }
    
    gc_assert(page_table[first_page].write_protected == 0);
    
    /*      fprintf(stderr,"  first_page=%d bytes_used=%d\n",first_page, page_table[first_page].bytes_used);*/
    
    last_page = first_page;
    bytes_found = 4096 - page_table[first_page].bytes_used;
    num_pages = 1;
    while ((bytes_found < nbytes)
	   && (last_page < (NUM_PAGES-1))
	   && (page_table[last_page+1].allocated == FREE_PAGE)) {
      last_page++;
      num_pages++;
      bytes_found += 4096;
      gc_assert(page_table[last_page].write_protected == 0);
    }
    
    region_size = (4096 - page_table[first_page].bytes_used)
      + 4096*(last_page-first_page);
    
    gc_assert(bytes_found == region_size);
    
    /*     fprintf(stderr,"  last_page=%d bytes_found=%d num_pages=%d\n",last_page, bytes_found, num_pages);*/
    
    restart_page = last_page + 1;
  }
  while ((restart_page < NUM_PAGES) && (bytes_found < nbytes));
  
  /* Check for a failure */
  if ((restart_page >= NUM_PAGES) && (bytes_found < nbytes)) {
    fprintf(stderr,"*A1 gc_alloc_large failed, nbytes=%d.\n", nbytes);
    print_generation_stats(1);
    exit(1);
  }
  
  /*  if (large)
    fprintf(stderr,"gc_alloc_large gen %d: %d of %d bytes: from pages %d to %d: addr=%x\n",
	    gc_alloc_generation, nbytes, bytes_found,
	    first_page, last_page, page_address(first_page));*/

  gc_assert(first_page > alloc_region->last_page);
  if (unboxed)
    generations[gc_alloc_generation].alloc_large_unboxed_start_page =
      last_page;
  else
    generations[gc_alloc_generation].alloc_large_start_page = last_page;

  /* Setup the pages. */
  orig_first_page_bytes_used = page_table[first_page].bytes_used;
  
  /* If the first page was free then setup the gen, and
     first_object_offset. */
  if (page_table[first_page].bytes_used == 0) {
    if (unboxed)
      page_table[first_page].allocated = UNBOXED_PAGE;
    else
      page_table[first_page].allocated = BOXED_PAGE;
    page_table[first_page].gen = gc_alloc_generation;
    page_table[first_page].first_object_offset = 0;
    page_table[first_page].large_object = large;
  }

  if (unboxed)
    gc_assert(page_table[first_page].allocated == UNBOXED_PAGE);
  else
    gc_assert(page_table[first_page].allocated == BOXED_PAGE);
  gc_assert(page_table[first_page].gen == gc_alloc_generation);
  gc_assert(page_table[first_page].large_object == large);
  
  byte_cnt = 0;
      
  /* Calc. the number of bytes used in this page. This is not
     always the number of new bytes, unless it was free. */
  more = 0;
  if ((bytes_used = nbytes+orig_first_page_bytes_used) > 4096) {
    bytes_used = 4096;
    more = 1;
  }
  page_table[first_page].bytes_used = bytes_used;
  byte_cnt += bytes_used;

  next_page = first_page+1;

  /* All the rest of the pages should be free. Need to set their
     first_object_offset pointer to the start of the region, and
     set the bytes_used. */
  while (more) {
    /*      fprintf(stderr,"+");*/
    
    gc_assert(page_table[next_page].allocated == FREE_PAGE);
    gc_assert(page_table[next_page].bytes_used == 0);
    if (unboxed)
      page_table[next_page].allocated = UNBOXED_PAGE;
    else
      page_table[next_page].allocated = BOXED_PAGE;
    page_table[next_page].gen = gc_alloc_generation;
    page_table[next_page].large_object = large;
    
    page_table[next_page].first_object_offset =
      orig_first_page_bytes_used - 4096*(next_page-first_page);
    
    /* Calc. the number of bytes used in this page. */
    more = 0;
    if ((bytes_used=(nbytes+orig_first_page_bytes_used)-byte_cnt) > 4096) {
      bytes_used = 4096;
      more = 1;
    }
    page_table[next_page].bytes_used = bytes_used;
    byte_cnt += bytes_used;
    
    next_page++;
  }
  
  gc_assert((byte_cnt-orig_first_page_bytes_used) == nbytes);

  bytes_allocated += nbytes;
  generations[gc_alloc_generation].bytes_allocated += nbytes;

  /* Add the region to the new_areas if requested. */
  if (!unboxed)
    add_new_area(first_page,orig_first_page_bytes_used,nbytes);
  
  /* Bump up last_free_page */
  if (last_page+1 > last_free_page) {
    last_free_page = last_page+1;
    SetSymbolValue(ALLOCATION_POINTER,
		   (lispobj)(((char *)heap_base) + last_free_page*4096));
    if (last_page+1 > last_used_page)
      last_used_page = last_page+1;
  }
  
  return((void *)(page_address(first_page)+orig_first_page_bytes_used));
}