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ocaml/byterun/major_gc.c

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/***********************************************************************/
/* */
/* 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, with */
/* the special exception on linking described in file ../LICENSE. */
/* */
/***********************************************************************/
/* $Id$ */
#include <limits.h>
#include "compact.h"
#include "custom.h"
#include "config.h"
#include "fail.h"
#include "finalise.h"
#include "freelist.h"
#include "gc.h"
#include "gc_ctrl.h"
#include "major_gc.h"
#include "misc.h"
#include "mlvalues.h"
#include "roots.h"
#include "weak.h"
unsigned long percent_free;
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; /* always Phase_mark, Phase_sweep, or Phase_idle */
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;
unsigned long fl_size_at_phase_change = 0;
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);
if (Is_block (child) && Is_in_heap (child)) {
hd = Hd_val (child);
if (Tag_hd (hd) == Forward_tag){
value f = Forward_val (child);
if (Is_block (f) && (Is_young (f) || Is_in_heap (f))
&& (Tag_val (f) == Forward_tag || Tag_val (f) == Lazy_tag)){
/* Do not short-circuit the pointer. */
}else{
Field (v, i) = f;
}
}
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 != (value) NULL){
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)){
if (Tag_val (curfield) == Forward_tag){
value f = Forward_val (curfield);
if (Is_block (f) && (Is_young (f) || Is_in_heap (f))){
if (Tag_val (f) == Forward_tag || Tag_val (f) == Lazy_tag){
/* Do not short-circuit the pointer. */
}else{
Field (cur, i) = curfield = f;
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;
fl_size_at_phase_change = fl_cur_size;
}
}
gray_vals_cur = gray_vals_ptr;
}
static void sweep_slice (long 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)
/ Wsize_bsize (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 * Wsize_bsize (stat_heap_size) * 100
/ (100+percent_free));
}else{
computed_work = 2 * (long) (p * Wsize_bsize (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;
}
/* Make sure the request is at least Heap_chunk_min and round it up
to a multiple of the page size.
*/
static asize_t clip_heap_chunk_size (asize_t request)
{
if (request < Bsize_wsize (Heap_chunk_min)){
request = Bsize_wsize (Heap_chunk_min);
}
return ((request + Page_size - 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 ();
return 0; /* not reached */
}
return result;
}
void init_major_heap (asize_t heap_size)
{
asize_t i;
void *block;
asize_t page_table_size;
page_table_entry *page_table_block;
stat_heap_size = clip_heap_chunk_size (heap_size);
stat_top_heap_size = stat_heap_size;
Assert (stat_heap_size % Page_size == 0);
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");
Chunk_next (heap_start) = NULL;
heap_end = heap_start + stat_heap_size;
Assert ((unsigned long) heap_end % Page_size == 0);
stat_heap_chunks = 1;
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;
}
fl_init_merge ();
make_free_blocks ((value *) heap_start, Wsize_bsize (stat_heap_size), 1);
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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