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ocaml/byterun/compact.c

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/***********************************************************************/
/* */
/* OCaml */
/* */
/* 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 <string.h>
#include "config.h"
#include "finalise.h"
#include "freelist.h"
#include "gc.h"
#include "gc_ctrl.h"
#include "major_gc.h"
#include "memory.h"
#include "mlvalues.h"
#include "roots.h"
#include "weak.h"
extern uintnat caml_percent_free; /* major_gc.c */
extern void caml_shrink_heap (char *); /* memory.c */
/* Encoded headers: the color is stored in the 2 least significant bits.
(For pointer inversion, we need to distinguish headers from pointers.)
s is a Wosize, t is a tag, and c is a color (a two-bit number)
For the purpose of compaction, "colors" are:
0: pointers (direct or inverted)
1: integer or (unencoded) infix header
2: inverted pointer for infix header
3: integer or encoded (noninfix) header
XXX Should be fixed:
XXX The above assumes that all roots are aligned on a 4-byte boundary,
XXX which is not always guaranteed by C.
XXX (see [caml_register_global_roots] and [caml_init_exceptions])
XXX Should be able to fix it to only assume 2-byte alignment.
*/
#define Make_ehd(s,t,c) (((s) << 10) | (t) << 2 | (c))
#define Whsize_ehd(h) Whsize_hd (h)
#define Wosize_ehd(h) Wosize_hd (h)
#define Tag_ehd(h) (((h) >> 2) & 0xFF)
#define Ecolor(w) ((w) & 3)
typedef uintnat word;
static void invert_pointer_at (word *p)
{
word q = *p;
Assert (Ecolor ((intnat) p) == 0);
/* Use Ecolor (q) == 0 instead of Is_block (q) because q could be an
inverted pointer for an infix header (with Ecolor == 2). */
if (Ecolor (q) == 0 && (Classify_addr (q) & In_heap)){
switch (Ecolor (Hd_val (q))){
case 0:
case 3: /* Pointer or header: insert in inverted list. */
*p = Hd_val (q);
Hd_val (q) = (header_t) p;
break;
case 1: /* Infix header: make inverted infix list. */
/* Double inversion: the last of the inverted infix list points to
the next infix header in this block. The last of the last list
contains the original block header. */
{
/* This block as a value. */
value val = (value) q - Infix_offset_val (q);
/* Get the block header. */
word *hp = (word *) Hp_val (val);
while (Ecolor (*hp) == 0) hp = (word *) *hp;
Assert (Ecolor (*hp) == 3);
if (Tag_ehd (*hp) == Closure_tag){
/* This is the first infix found in this block. */
/* Save original header. */
*p = *hp;
/* Link inverted infix list. */
Hd_val (q) = (header_t) ((word) p | 2);
/* Change block header's tag to Infix_tag, and change its size
to point to the infix list. */
*hp = Make_ehd (Wosize_bhsize (q - val), Infix_tag, 3);
}else{ Assert (Tag_ehd (*hp) == Infix_tag);
/* Point the last of this infix list to the current first infix
list of the block. */
*p = (word) &Field (val, Wosize_ehd (*hp)) | 1;
/* Point the head of this infix list to the above. */
Hd_val (q) = (header_t) ((word) p | 2);
/* Change block header's size to point to this infix list. */
*hp = Make_ehd (Wosize_bhsize (q - val), Infix_tag, 3);
}
}
break;
case 2: /* Inverted infix list: insert. */
*p = Hd_val (q);
Hd_val (q) = (header_t) ((word) p | 2);
break;
}
}
}
static void invert_root (value v, value *p)
{
invert_pointer_at ((word *) p);
}
static char *compact_fl;
static void init_compact_allocate (void)
{
char *ch = caml_heap_start;
while (ch != NULL){
Chunk_alloc (ch) = 0;
ch = Chunk_next (ch);
}
compact_fl = caml_heap_start;
}
static char *compact_allocate (mlsize_t size)
/* in bytes, including header */
{
char *chunk, *adr;
while (Chunk_size (compact_fl) - Chunk_alloc (compact_fl) <= Bhsize_wosize (3)
&& Chunk_size (Chunk_next (compact_fl))
- Chunk_alloc (Chunk_next (compact_fl))
<= Bhsize_wosize (3)){
compact_fl = Chunk_next (compact_fl);
}
chunk = compact_fl;
while (Chunk_size (chunk) - Chunk_alloc (chunk) < size){
chunk = Chunk_next (chunk); Assert (chunk != NULL);
}
adr = chunk + Chunk_alloc (chunk);
Chunk_alloc (chunk) += size;
return adr;
}
void caml_compact_heap (void)
{
char *ch, *chend;
Assert (caml_gc_phase == Phase_idle);
caml_gc_message (0x10, "Compacting heap...\n", 0);
#ifdef DEBUG
caml_heap_check ();
#endif
/* First pass: encode all noninfix headers. */
{
ch = caml_heap_start;
while (ch != NULL){
header_t *p = (header_t *) ch;
chend = ch + Chunk_size (ch);
while ((char *) p < chend){
header_t hd = Hd_hp (p);
mlsize_t sz = Wosize_hd (hd);
if (Is_blue_hd (hd)){
/* Free object. Give it a string tag. */
Hd_hp (p) = Make_ehd (sz, String_tag, 3);
}else{ Assert (Is_white_hd (hd));
/* Live object. Keep its tag. */
Hd_hp (p) = Make_ehd (sz, Tag_hd (hd), 3);
}
p += Whsize_wosize (sz);
}
ch = Chunk_next (ch);
}
}
/* Second pass: invert pointers.
Link infix headers in each block in an inverted list of inverted lists.
Don't forget roots and weak pointers. */
{
/* Invert roots first because the threads library needs some heap
data structures to find its roots. Fortunately, it doesn't need
the headers (see above). */
caml_do_roots (invert_root);
caml_final_do_weak_roots (invert_root);
ch = caml_heap_start;
while (ch != NULL){
word *p = (word *) ch;
chend = ch + Chunk_size (ch);
while ((char *) p < chend){
word q = *p;
size_t sz, i;
tag_t t;
word *infixes;
while (Ecolor (q) == 0) q = * (word *) q;
sz = Whsize_ehd (q);
t = Tag_ehd (q);
if (t == Infix_tag){
/* Get the original header of this block. */
infixes = p + sz;
q = *infixes;
while (Ecolor (q) != 3) q = * (word *) (q & ~(uintnat)3);
sz = Whsize_ehd (q);
t = Tag_ehd (q);
}
if (t < No_scan_tag){
for (i = 1; i < sz; i++) invert_pointer_at (&(p[i]));
}
p += sz;
}
ch = Chunk_next (ch);
}
/* Invert weak pointers. */
{
value *pp = &caml_weak_list_head;
value p;
word q;
size_t sz, i;
while (1){
p = *pp;
if (p == (value) NULL) break;
q = Hd_val (p);
while (Ecolor (q) == 0) q = * (word *) q;
sz = Wosize_ehd (q);
for (i = 1; i < sz; i++){
if (Field (p,i) != caml_weak_none){
invert_pointer_at ((word *) &(Field (p,i)));
}
}
invert_pointer_at ((word *) pp);
pp = &Field (p, 0);
}
}
}
/* Third pass: reallocate virtually; revert pointers; decode headers.
Rebuild infix headers. */
{
init_compact_allocate ();
ch = caml_heap_start;
while (ch != NULL){
word *p = (word *) ch;
chend = ch + Chunk_size (ch);
while ((char *) p < chend){
word q = *p;
if (Ecolor (q) == 0 || Tag_ehd (q) == Infix_tag){
/* There were (normal or infix) pointers to this block. */
size_t sz;
tag_t t;
char *newadr;
word *infixes = NULL;
while (Ecolor (q) == 0) q = * (word *) q;
sz = Whsize_ehd (q);
t = Tag_ehd (q);
if (t == Infix_tag){
/* Get the original header of this block. */
infixes = p + sz;
q = *infixes; Assert (Ecolor (q) == 2);
while (Ecolor (q) != 3) q = * (word *) (q & ~(uintnat)3);
sz = Whsize_ehd (q);
t = Tag_ehd (q);
}
newadr = compact_allocate (Bsize_wsize (sz));
q = *p;
while (Ecolor (q) == 0){
word next = * (word *) q;
* (word *) q = (word) Val_hp (newadr);
q = next;
}
*p = Make_header (Wosize_whsize (sz), t, Caml_white);
if (infixes != NULL){
/* Rebuild the infix headers and revert the infix pointers. */
while (Ecolor ((word) infixes) != 3){
infixes = (word *) ((word) infixes & ~(uintnat) 3);
q = *infixes;
while (Ecolor (q) == 2){
word next;
q = (word) q & ~(uintnat) 3;
next = * (word *) q;
* (word *) q = (word) Val_hp ((word *) newadr + (infixes - p));
q = next;
} Assert (Ecolor (q) == 1 || Ecolor (q) == 3);
*infixes = Make_header (infixes - p, Infix_tag, Caml_white);
infixes = (word *) q;
}
}
p += sz;
}else{ Assert (Ecolor (q) == 3);
/* This is guaranteed only if caml_compact_heap was called after a
nonincremental major GC: Assert (Tag_ehd (q) == String_tag);
*/
/* No pointers to the header and no infix header:
the object was free. */
*p = Make_header (Wosize_ehd (q), Tag_ehd (q), Caml_blue);
p += Whsize_ehd (q);
}
}
ch = Chunk_next (ch);
}
}
/* Fourth pass: reallocate and move objects.
Use the exact same allocation algorithm as pass 3. */
{
init_compact_allocate ();
ch = caml_heap_start;
while (ch != NULL){
word *p = (word *) ch;
chend = ch + Chunk_size (ch);
while ((char *) p < chend){
word q = *p;
if (Color_hd (q) == Caml_white){
size_t sz = Bhsize_hd (q);
char *newadr = compact_allocate (sz); Assert (newadr <= (char *)p);
memmove (newadr, p, sz);
p += Wsize_bsize (sz);
}else{
Assert (Color_hd (q) == Caml_blue);
p += Whsize_hd (q);
}
}
ch = Chunk_next (ch);
}
}
/* Shrink the heap if needed. */
{
/* Find the amount of live data and the unshrinkable free space. */
asize_t live = 0;
asize_t free = 0;
asize_t wanted;
ch = caml_heap_start;
while (ch != NULL){
if (Chunk_alloc (ch) != 0){
live += Wsize_bsize (Chunk_alloc (ch));
free += Wsize_bsize (Chunk_size (ch) - Chunk_alloc (ch));
}
ch = Chunk_next (ch);
}
/* Add up the empty chunks until there are enough, then remove the
other empty chunks. */
wanted = caml_percent_free * (live / 100 + 1);
ch = caml_heap_start;
while (ch != NULL){
char *next_chunk = Chunk_next (ch); /* Chunk_next (ch) will be erased */
if (Chunk_alloc (ch) == 0){
if (free < wanted){
free += Wsize_bsize (Chunk_size (ch));
}else{
caml_shrink_heap (ch);
}
}
ch = next_chunk;
}
}
/* Rebuild the free list. */
{
ch = caml_heap_start;
caml_fl_reset ();
while (ch != NULL){
if (Chunk_size (ch) > Chunk_alloc (ch)){
caml_make_free_blocks ((value *) (ch + Chunk_alloc (ch)),
Wsize_bsize (Chunk_size(ch)-Chunk_alloc(ch)), 1);
}
ch = Chunk_next (ch);
}
}
++ caml_stat_compactions;
caml_gc_message (0x10, "done.\n", 0);
}
uintnat caml_percent_max; /* used in gc_ctrl.c and memory.c */
void caml_compact_heap_maybe (void)
{
/* Estimated free words in the heap:
FW = fl_size_at_change + 3 * (caml_fl_cur_size
- caml_fl_size_at_phase_change)
FW = 3 * caml_fl_cur_size - 2 * caml_fl_size_at_phase_change
Estimated live words: LW = caml_stat_heap_size - FW
Estimated free percentage: FP = 100 * FW / LW
We compact the heap if FP > caml_percent_max
*/
float fw, fp;
Assert (caml_gc_phase == Phase_idle);
if (caml_percent_max >= 1000000) return;
if (caml_stat_major_collections < 3 || caml_stat_heap_chunks < 3) return;
fw = 3.0 * caml_fl_cur_size - 2.0 * caml_fl_size_at_phase_change;
if (fw < 0) fw = caml_fl_cur_size;
if (fw >= Wsize_bsize (caml_stat_heap_size)){
fp = 1000000.0;
}else{
fp = 100.0 * fw / (Wsize_bsize (caml_stat_heap_size) - fw);
if (fp > 1000000.0) fp = 1000000.0;
}
caml_gc_message (0x200, "FL size at phase change = %"
ARCH_INTNAT_PRINTF_FORMAT "u\n",
(uintnat) caml_fl_size_at_phase_change);
caml_gc_message (0x200, "Estimated overhead = %"
ARCH_INTNAT_PRINTF_FORMAT "u%%\n",
(uintnat) fp);
if (fp >= caml_percent_max){
caml_gc_message (0x200, "Automatic compaction triggered.\n", 0);
caml_finish_major_cycle ();
/* We just did a complete GC, so we can measure the overhead exactly. */
fw = caml_fl_cur_size;
fp = 100.0 * fw / (Wsize_bsize (caml_stat_heap_size) - fw);
caml_gc_message (0x200, "Measured overhead: %"
ARCH_INTNAT_PRINTF_FORMAT "u%%\n",
(uintnat) fp);
caml_compact_heap ();
}
}
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