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major_gc.c

/***********************************************************************/
/*                                                                     */
/*                           Objective Caml                            */
/*                                                                     */
/*             Damien Doligez, projet Para, INRIA Rocquencourt         */
/*                                                                     */
/*  Copyright 1996 Institut National de Recherche en Informatique et   */
/*  en Automatique.  All rights reserved.  This file is distributed    */
/*  under the terms of the GNU Library General Public License.         */
/*                                                                     */
/***********************************************************************/

/***---------------------------------------------------------------------
  Modified and adapted for the Lazy Virtual Machine by Daan Leijen.
  Modifications copyright 2001, Daan Leijen. This (modified) file is
  distributed under the terms of the GNU Library General Public License.
---------------------------------------------------------------------***/

/* $Id: major_gc.c 177 2002-11-15 16:21:56Z cvs-3 $ */

#include <limits.h>

#include "mlvalues.h"
#include "compact.h"
#include "custom.h"
#include "config.h"
#include "fail.h"
#include "finalise.h"
#include "heap.h"
#include "weak.h"

unsigned long percent_free;
/* LVM: changed [long] to [unsigned long] */
unsigned long major_heap_increment;
char *heap_start, *heap_end;
page_table_entry *page_table;
asize_t page_low, page_high;
char *gc_sweep_hp;
int gc_phase;
static value *gray_vals;
value *gray_vals_cur, *gray_vals_end;
static asize_t gray_vals_size;
static int heap_is_pure;   /* The heap is pure if the only gray objects
                              below [markhp] are also in [gray_vals]. */
unsigned long allocated_words;
double extra_heap_memory;
extern char *fl_merge;  /* Defined in freelist.c. */

static char *markhp, *chunk, *limit;

static int gc_subphase;     /* Subphase_main, Subphase_weak, Subphase_final */
#define Subphase_main 10
#define Subphase_weak 11
#define Subphase_final 12
static value *weak_prev;

static void realloc_gray_vals (void)
{
  value *new;

  Assert (gray_vals_cur == gray_vals_end);
  if (gray_vals_size < stat_heap_size / 128){
    gc_message (0x08, "Growing gray_vals to %luk bytes\n",
                (long) gray_vals_size * sizeof (value) / 512);
    new = (value *) realloc ((char *) gray_vals,
                             2 * gray_vals_size * sizeof (value));
    if (new == NULL){
      gc_message (0x08, "No room for growing gray_vals\n", 0);
      gray_vals_cur = gray_vals;
      heap_is_pure = 0;
    }else{
      gray_vals = new;
      gray_vals_cur = gray_vals + gray_vals_size;
      gray_vals_size *= 2;
      gray_vals_end = gray_vals + gray_vals_size;
    }
  }else{
    gray_vals_cur = gray_vals + gray_vals_size / 2;
    heap_is_pure = 0;
  }
}

void darken (value v, value *p /* not used */)
{
  if (Is_block (v) && Is_in_heap (v)) {
    if (Tag_val(v) == Infix_tag) v -= Infix_offset_val(v);
    if (Is_white_val (v)){
      Hd_val (v) = Grayhd_hd (Hd_val (v));
      *gray_vals_cur++ = v;
      if (gray_vals_cur >= gray_vals_end) realloc_gray_vals ();
    }
  }
}

static void start_cycle (void)
{
  Assert (gc_phase == Phase_idle);
  Assert (gray_vals_cur == gray_vals);
  gc_message (0x01, "Starting new major GC cycle\n", 0);
  darken_all_roots();
  gc_phase = Phase_mark;
  gc_subphase = Subphase_main;
  markhp = NULL;
#ifdef DEBUG
  heap_check ();
#endif
}

static void mark_slice (long work)
{
  value *gray_vals_ptr;  /* Local copy of gray_vals_cur */
  value v, child;
  header_t hd;
  mlsize_t size, i;

  gc_message (0x40, "Marking %ld words\n", work);
  gray_vals_ptr = gray_vals_cur;
  while (work > 0){
    if (gray_vals_ptr > gray_vals){
      v = *--gray_vals_ptr;
      hd = Hd_val(v);
      Assert (Is_gray_hd (hd));
      Hd_val (v) = Blackhd_hd (hd);
      size = Wosize_hd(hd);
      if (Tag_hd (hd) < No_scan_tag){
        for (i = 0; i < size; i++){
          child = Field (v, i);
        /* mark_again: */
          if (Is_block (child) && Is_in_heap (child)) {
            hd = Hd_val(child);
            if (Tag_hd (hd) == Forward_tag){
              /* child = Forward_val (child);
              Field (v, i) = child;
              goto mark_again;
              */
              Field(v,i) = Forward_val(child);
            }
            else if (Tag_hd(hd) == Infix_tag) {
              child -= Infix_offset_val(child);
              hd = Hd_val(child);
            }
            if (Is_white_hd (hd)){
              Hd_val (child) = Grayhd_hd (hd);
              *gray_vals_ptr++ = child;
              if (gray_vals_ptr >= gray_vals_end) {
                gray_vals_cur = gray_vals_ptr;
                realloc_gray_vals ();
                gray_vals_ptr = gray_vals_cur;
              }
            }
          }
        }
      }
      work -= Whsize_wosize(size);
    }else if (markhp != NULL){
      if (markhp == limit){
        chunk = Chunk_next (chunk);
        if (chunk == NULL){
          markhp = NULL;
        }else{
          markhp = chunk;
          limit = chunk + Chunk_size (chunk);
        }
      }else{
        if (Is_gray_val (Val_hp (markhp))){
          Assert (gray_vals_ptr == gray_vals);
          *gray_vals_ptr++ = Val_hp (markhp);
        }
        markhp += Bhsize_hp (markhp);
      }
    }else if (!heap_is_pure){
      heap_is_pure = 1;
      chunk = heap_start;
      markhp = chunk;
      limit = chunk + Chunk_size (chunk);
    }else if (gc_subphase == Subphase_main){
      /* The main marking phase is over.  Start removing weak pointers to
         dead values. */
      gc_subphase = Subphase_weak;
      weak_prev = &weak_list_head;
    }else if (gc_subphase == Subphase_weak){
      value cur, curfield;
      mlsize_t sz, i;
      header_t hd;

      cur = *weak_prev;
      if (cur != 0){
        hd = Hd_val (cur);
        if (Color_hd (hd) == Caml_white){
          /* The whole array is dead, remove it from the list. */
          *weak_prev = Field (cur, 0);
        }else{
          sz = Wosize_hd (hd);
          for (i = 1; i < sz; i++){
            curfield = Field (cur, i);
          weak_again:
            if (curfield != 0 && Is_block (curfield) && Is_in_heap (curfield)) {
               /* && Is_white_val (curfield)){ */
              if (Tag_val (curfield) == Forward_tag){
                curfield = Forward_val (curfield);
                Field (cur, i) = curfield;
                goto weak_again;
              }
              if (Is_white_val(curfield)){
                Field (cur, i) = 0;
              }
            }
          }
          weak_prev = &Field (cur, 0);
        }
        work -= Whsize_hd (hd);
      }else{
        /* Subphase_weak is done.  Handle finalised values. */
        gray_vals_cur = gray_vals_ptr;
        final_update ();
        gray_vals_ptr = gray_vals_cur;
        gc_subphase = Subphase_final;
      }
    }else{
      Assert (gc_subphase == Subphase_final);
      /* Initialise the sweep phase. */
      gray_vals_cur = gray_vals_ptr;
      gc_sweep_hp = heap_start;
      fl_init_merge ();
      gc_phase = Phase_sweep;
      chunk = heap_start;
      gc_sweep_hp = chunk;
      limit = chunk + Chunk_size (chunk);
      work = 0;
    }
  }
  gray_vals_cur = gray_vals_ptr;
}

static void sweep_slice (long int work)
{
  char *hp;
  header_t hd;

  gc_message (0x40, "Sweeping %ld words\n", work);
  while (work > 0){
    if (gc_sweep_hp < limit){
      hp = gc_sweep_hp;
      hd = Hd_hp (hp);
      work -= Whsize_hd (hd);
      gc_sweep_hp += Bhsize_hd (hd);
      switch (Color_hd (hd)){
      case Caml_white:
        if (Tag_hd (hd) == Custom_tag){
          void (*final_fun)(value) = Custom_ops_val(Val_hp(hp))->finalize;
          if (final_fun != NULL) final_fun(Val_hp(hp));
        }
        gc_sweep_hp = fl_merge_block (Bp_hp (hp));
        break;
      case Caml_blue:
        /* Only the blocks of the free-list are blue.  See [freelist.c]. */
        fl_merge = Bp_hp (hp);
        break;
      default:          /* gray or black */
        Assert (Color_hd (hd) == Caml_black);
        Hd_hp (hp) = Whitehd_hd (hd);
        break;
      }
      Assert (gc_sweep_hp <= limit);
    }else{
      chunk = Chunk_next (chunk);
      if (chunk == NULL){
        /* Sweeping is done. */
        ++ stat_major_collections;
        work = 0;
        gc_phase = Phase_idle;
      }else{
        gc_sweep_hp = chunk;
        limit = chunk + Chunk_size (chunk);
      }
    }
  }
}

/* The main entry point for the GC.  Called after each minor GC.
   [howmuch] is the amount of work to do, 0 to let the GC compute it.
   Return the computed amount of work to do.
 */
long major_collection_slice (long howmuch)
{
  double p;
  long computed_work;
  /*
     Free memory at the start of the GC cycle (garbage + free list) (assumed):
                 FM = stat_heap_size * percent_free / (100 + percent_free)
     Assuming steady state and enforcing a constant allocation rate, then
     FM is divided in 2/3 for garbage and 1/3 for free list.
                 G = 2 * FM / 3
     G is also the amount of memory that will be used during this slice
     (still assuming steady state).

     Proportion of G consumed since the previous slice:
                 PH = allocated_words / G
                    = allocated_words * 3 * (100 + percent_free)
                      / (2 * stat_heap_size * percent_free)
     Proportion of extra-heap memory consumed since the previous slice:
                 PE = extra_heap_memory
     Proportion of total work to do in this slice:
                 P  = max (PH, PE)
     Amount of marking work for the GC cycle:
                 MW = stat_heap_size * 100 / (100 + percent_free)
     Amount of sweeping work for the GC cycle:
                 SW = stat_heap_size
     Amount of marking work for this slice:
                 MS = P * MW
                 MS = P * stat_heap_size * 100 / (100 + percent_free)
     Amount of sweeping work for this slice:
                 SS = P * SW
                 SS = P * stat_heap_size
     This slice will either mark 2*MS words or sweep 2*SS words.
  */


  if (gc_phase == Phase_idle) start_cycle ();

  p = (double) allocated_words * 3.0 * (100 + percent_free)
      / stat_heap_size / percent_free / 2.0;
  if (p < extra_heap_memory) p = extra_heap_memory;

  gc_message (0x40, "allocated_words = %lu\n", allocated_words);
  gc_message (0x40, "extra_heap_memory = %luu\n",
              (unsigned long) (extra_heap_memory * 1000000));
  gc_message (0x40, "amount of work to do = %luu\n",
              (unsigned long) (p * 1000000));

  if (gc_phase == Phase_mark){
    computed_work = 2 * (long) (p * stat_heap_size * 100 / (100+percent_free));
  }else{
    computed_work = 2 * (long) (p * stat_heap_size);
  }

  gc_message (0x40, "ordered work = %ld words\n", howmuch);
  gc_message (0x40, "computed work = %ld words\n", computed_work);
  if (howmuch == 0) howmuch = computed_work;
  if (gc_phase == Phase_mark){
    mark_slice (howmuch);
    gc_message (0x02, "!", 0);
  }else{
    Assert (gc_phase == Phase_sweep);
    sweep_slice (howmuch);
    gc_message (0x02, "$", 0);
  }

  if (gc_phase == Phase_idle) compact_heap_maybe ();

  stat_major_words += allocated_words;
  allocated_words = 0;
  extra_heap_memory = 0.0;
  return computed_work;
}

/* The minor heap must be empty when this function is called;
   the minor heap is empty when this function returns.
*/
/* This does not call compact_heap_maybe because the estimations of
   free and live memory are only valid for a cycle done incrementally.
   Besides, this function is called by compact_heap_maybe.
*/
void finish_major_cycle (void)
{
  if (gc_phase == Phase_idle) start_cycle ();
  while (gc_phase == Phase_mark) mark_slice (LONG_MAX);
  Assert (gc_phase == Phase_sweep);
  while (gc_phase == Phase_sweep) sweep_slice (LONG_MAX);
  Assert (gc_phase == Phase_idle);
  stat_major_words += allocated_words;
  allocated_words = 0;
}

/* Clip the request to [Heap_chunk_min..Heap_chunk_max] and round it
   to a multiple of the page size.
*/
static asize_t clip_heap_chunk_size (asize_t request)
{                             Assert (Heap_chunk_max_wsize >= Heap_chunk_min_wsize);
                              Assert (Heap_chunk_min_wsize <= major_heap_increment);
  if (request < major_heap_increment){
    request = major_heap_increment;
  }
  if (request > Heap_chunk_max_wsize){
    request = Heap_chunk_max_wsize;
  }
  return ((request + Page_bsize - 1) >> Page_log) << Page_log;
}

/* Make sure the request is >= major_heap_increment, then call
   clip_heap_chunk_size, then make sure the result is >= request.
*/
asize_t round_heap_chunk_size (asize_t request)
{
  asize_t result = request;

  if (result < major_heap_increment){
    result = major_heap_increment;
  }
  result = clip_heap_chunk_size (result);

  if (result < request){
    raise_out_of_memory (stat_heap_size);
    return 0; /* not reached */
  }
  return result;
}


void init_major_heap (asize_t heap_size)
{
  asize_t i;
  asize_t page_table_size;
  page_table_entry *page_table_block;

  stat_peak_heap_bsize = stat_heap_size = clip_heap_chunk_size (heap_size);
  Assert (stat_heap_size % Page_bsize == 0);
  /* heap_start = aligned_malloc (stat_heap_size + sizeof (heap_chunk_head),
                               sizeof (heap_chunk_head), &block); */
  heap_start = (char *) alloc_for_heap(stat_heap_size);
  if (heap_start == NULL)
    fatal_error ("Fatal error: not enough memory for the initial heap.\n");
/*
  heap_start += sizeof (heap_chunk_head);
  Assert ((unsigned long) heap_start % Page_bsize == 0);
  Chunk_size (heap_start) = stat_heap_size;
*/
  Chunk_next (heap_start) = NULL;
/*  Chunk_block (heap_start) = block; */
  heap_end = heap_start + stat_heap_size;
  Assert ((unsigned long) heap_end % Page_bsize == 0);

  page_low = Page (heap_start);
  page_high = Page (heap_end);

  page_table_size = page_high - page_low;
  page_table_block =
    (page_table_entry *) malloc (page_table_size * sizeof (page_table_entry));
  if (page_table_block == NULL){
    fatal_error ("Fatal error: not enough memory for the initial heap.\n");
  }
  page_table = page_table_block - page_low;
  for (i = Page (heap_start); i < Page (heap_end); i++){
    page_table [i] = In_heap;
  }

  Hd_hp (heap_start) = Make_header (Wosize_bhsize (stat_heap_size), 0, Caml_blue);
  fl_init_merge ();
  fl_merge_block (Bp_hp (heap_start));
  gc_phase = Phase_idle;
  gray_vals_size = 2048;
  gray_vals = (value *) malloc (gray_vals_size * sizeof (value));
  if (gray_vals == NULL)
    fatal_error ("Fatal error: not enough memory for the initial heap.\n");
  gray_vals_cur = gray_vals;
  gray_vals_end = gray_vals + gray_vals_size;
  heap_is_pure = 1;
  allocated_words = 0;
  extra_heap_memory = 0.0;
}

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