/
major_gc.c
1179 lines (1035 loc) · 37.1 KB
/
major_gc.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 Lesser General Public License version 2.1, with the */
/* special exception on linking described in the file LICENSE. */
/* */
/**************************************************************************/
#define CAML_INTERNALS
#include <limits.h>
#include <math.h>
#include "caml/compact.h"
#include "caml/custom.h"
#include "caml/config.h"
#include "caml/fail.h"
#include "caml/finalise.h"
#include "caml/freelist.h"
#include "caml/gc.h"
#include "caml/gc_ctrl.h"
#include "caml/major_gc.h"
#include "caml/misc.h"
#include "caml/mlvalues.h"
#include "caml/roots.h"
#include "caml/skiplist.h"
#include "caml/signals.h"
#include "caml/weak.h"
#include "caml/memprof.h"
#include "caml/eventlog.h"
#ifdef _MSC_VER
Caml_inline double fmin(double a, double b) {
return (a < b) ? a : b;
}
#endif
#define MARK_STACK_INIT_SIZE 2048
typedef struct {
value block;
uintnat offset;
} mark_entry;
struct mark_stack {
mark_entry* stack;
uintnat count;
uintnat size;
};
uintnat caml_percent_free;
uintnat caml_major_heap_increment;
CAMLexport char *caml_heap_start;
char *caml_gc_sweep_hp;
int caml_gc_phase; /* always Phase_mark, Pase_clean,
Phase_sweep, or Phase_idle */
uintnat caml_allocated_words;
uintnat caml_dependent_size, caml_dependent_allocated;
double caml_extra_heap_resources;
uintnat caml_fl_wsz_at_phase_change = 0;
extern value caml_fl_merge; /* Defined in freelist.c. */
/* redarken_first_chunk is the first chunk needing redarkening, if NULL no
redarkening required */
static char *redarken_first_chunk = NULL;
static char *sweep_chunk, *sweep_limit;
static double p_backlog = 0.0; /* backlog for the gc speedup parameter */
int caml_gc_subphase; /* Subphase_{mark_roots,mark_main,mark_final} */
/**
Ephemerons:
During mark phase the list caml_ephe_list_head of ephemerons
is iterated by different pointers that follow the invariants:
caml_ephe_list_head ->* ephes_checked_if_pure ->* ephes_to_check ->* null
| | |
(1) (2) (3)
At the start of mark phase, (1) and (2) are empty.
In mark phase:
- the ephemerons in (1) have a data alive or none
(nb: new ephemerons are added in this part by weak.c)
- the ephemerons in (2) have at least a white key or are white
if ephe_list_pure is true, otherwise they are in an unknown state and
must be checked again.
- the ephemerons in (3) are in an unknown state and must be checked
At the end of mark phase, (3) is empty and ephe_list_pure is true.
The ephemeron in (1) and (2) will be cleaned (white keys and data
replaced by none or the ephemeron is removed from the list if it is white)
in clean phase.
In clean phase:
caml_ephe_list_head ->* ephes_to_check ->* null
| |
(1) (3)
In clean phase, (2) is not used, ephes_to_check is initialized at
caml_ephe_list_head:
- the ephemerons in (1) are clean.
- the ephemerons in (3) should be cleaned or removed if white.
*/
static int ephe_list_pure;
/** The ephemerons is pure if since the start of its iteration
no value have been darkened. */
static value *ephes_checked_if_pure;
static value *ephes_to_check;
int caml_major_window = 1;
double caml_major_ring[Max_major_window] = { 0. };
int caml_major_ring_index = 0;
double caml_major_work_credit = 0.0;
double caml_gc_clock = 0.0;
#ifdef DEBUG
static unsigned long major_gc_counter = 0;
#endif
void (*caml_major_gc_hook)(void) = NULL;
/* This function prunes the mark stack if it's about to overflow. It does so
by building a skiplist of major heap chunks and then iterating through the
mark stack and setting redarken_start/redarken_end on each chunk to indicate
the range that requires redarkening. */
static void mark_stack_prune (struct mark_stack* stk)
{
int entry;
uintnat mark_stack_count = stk->count;
mark_entry* mark_stack = stk->stack;
char* heap_chunk = caml_heap_start;
struct skiplist chunk_sklist = SKIPLIST_STATIC_INITIALIZER;
do {
caml_skiplist_insert(&chunk_sklist, (uintnat)heap_chunk,
(uintnat)(heap_chunk+Chunk_size(heap_chunk)));
heap_chunk = Chunk_next(heap_chunk);
} while( heap_chunk != NULL );
for( entry = 0; entry < mark_stack_count ; entry++ ) {
mark_entry me = mark_stack[entry];
value* block_op = Op_val(me.block);
uintnat chunk_addr = 0, chunk_addr_below = 0;
if( caml_skiplist_find_below(&chunk_sklist, (uintnat)me.block,
&chunk_addr, &chunk_addr_below)
&& me.block < chunk_addr_below ) {
if( Chunk_redarken_start(chunk_addr) > block_op ) {
Chunk_redarken_start(chunk_addr) = block_op;
}
if( Chunk_redarken_end(chunk_addr) < block_op ) {
Chunk_redarken_end(chunk_addr) = block_op;
}
if( redarken_first_chunk == NULL
|| redarken_first_chunk > (char*)chunk_addr ) {
redarken_first_chunk = (char*)chunk_addr;
}
}
}
caml_skiplist_empty(&chunk_sklist);
caml_gc_message(0x08, "Mark stack overflow.\n");
stk->count = 0;
}
static void realloc_mark_stack (struct mark_stack* stk)
{
mark_entry* new;
uintnat mark_stack_bsize = stk->size * sizeof(mark_entry);
if ( Wsize_bsize(mark_stack_bsize) < Caml_state->stat_heap_wsz / 64 ) {
caml_gc_message (0x08, "Growing mark stack to %"
ARCH_INTNAT_PRINTF_FORMAT "uk bytes\n",
(intnat) mark_stack_bsize * 2 / 1024);
new = (mark_entry*) caml_stat_resize_noexc ((char*) stk->stack,
2 * mark_stack_bsize);
if (new != NULL) {
stk->stack = new;
stk->size *= 2;
return;
}
}
caml_gc_message (0x08, "No room for growing mark stack. Pruning..\n");
mark_stack_prune(stk);
}
/* This function pushes the provided mark_entry [me] onto the current mark
stack [stk]. It first checks, if the block is small enough, whether there
are any fields we would actually do mark work on. If so then it enqueues
the entry. */
Caml_inline void mark_stack_push(struct mark_stack* stk, value block,
uintnat offset, intnat* work)
{
value v;
int i, block_wsz = Wosize_val(block), end;
mark_entry* me;
CAMLassert(Is_block(block) && Is_in_heap (block)
&& Is_black_val(block));
CAMLassert(Tag_val(block) != Infix_tag);
CAMLassert(Tag_val(block) < No_scan_tag);
#if defined(NO_NAKED_POINTERS) || defined(NAKED_POINTERS_CHECKER)
if (Tag_val(block) == Closure_tag) {
/* Skip the code pointers and integers at beginning of closure;
start scanning at the first word of the environment part. */
/* It might be the case that [mark_stack_push] has been called
while we are traversing a closure block but have not enough
budget to finish the block. In that specific case, we should not
update [m.offset] */
if (offset == 0)
offset = Start_env_closinfo(Closinfo_val(block));
CAMLassert(offset <= Wosize_val(block)
&& offset >= Start_env_closinfo(Closinfo_val(block)));
}
#endif
end = (block_wsz < 8 ? block_wsz : 8);
/* Optimisation to avoid pushing small, unmarkable objects such as [Some 42]
* into the mark stack. */
for (i = offset; i < end; i++) {
v = Field(block, i);
if (Is_block(v) && !Is_young(v))
/* found something to mark */
break;
}
if (i == block_wsz) {
/* nothing left to mark */
if( work != NULL ) {
/* we should take credit for it though */
*work -= Whsize_wosize(block_wsz - offset);
}
return;
}
if( work != NULL ) {
/* take credit for the work we skipped due to the optimisation.
we will take credit for the header later as part of marking. */
*work -= (i - offset);
}
offset = i;
if (stk->count == stk->size)
realloc_mark_stack(stk);
me = &stk->stack[stk->count++];
me->block = block;
me->offset = offset;
}
#if defined(NAKED_POINTERS_CHECKER) && defined(NATIVE_CODE)
static void is_naked_pointer_safe (value v, value *p);
#endif
void caml_darken (value v, value *p)
{
#ifdef NO_NAKED_POINTERS
if (Is_block(v) && !Is_young (v)) {
#else
if (Is_block(v) && Is_in_heap (v)) {
#endif
header_t h = Hd_val (v);
tag_t t = Tag_hd (h);
if (t == Infix_tag){
v -= Infix_offset_val(v);
h = Hd_val (v);
t = Tag_hd (h);
}
#ifdef NO_NAKED_POINTERS
/* We insist that naked pointers to outside the heap point to things that
look like values with headers coloured black. This is always
strictly necessary because the compactor relies on it. */
CAMLassert (Is_in_heap (v) || Is_black_hd (h));
#endif
CAMLassert (!Is_blue_hd (h));
if (Is_white_hd (h)){
ephe_list_pure = 0;
Hd_val (v) = Blackhd_hd (h);
if (t < No_scan_tag){
mark_stack_push(Caml_state->mark_stack, v, 0, NULL);
}
}
}
#if defined(NAKED_POINTERS_CHECKER) && defined(NATIVE_CODE)
else if (Is_block(v) && !Is_young(v)) {
is_naked_pointer_safe(v, p);
}
#endif
}
/* This function shrinks the mark stack back to the MARK_STACK_INIT_SIZE size
and is called at the end of a GC compaction to avoid a mark stack greater
than 1/32th of the heap. */
void caml_shrink_mark_stack () {
struct mark_stack* stk = Caml_state->mark_stack;
intnat init_stack_bsize = MARK_STACK_INIT_SIZE * sizeof(mark_entry);
mark_entry* shrunk_stack;
caml_gc_message (0x08, "Shrinking mark stack to %"
ARCH_INTNAT_PRINTF_FORMAT "uk bytes\n",
init_stack_bsize);
shrunk_stack = (mark_entry*) caml_stat_resize_noexc ((char*) stk->stack,
init_stack_bsize);
if (shrunk_stack != NULL) {
stk->stack = shrunk_stack;
stk->size = MARK_STACK_INIT_SIZE;
}else{
caml_gc_message (0x08, "Mark stack shrinking failed");
}
}
/* This function adds blocks in the passed heap chunk [heap_chunk] to
the mark stack. It returns 1 when the supplied chunk has no more
range to redarken. It returns 0 if there are still blocks in the
chunk that need redarkening because pushing them onto the stack
would make it grow more than a quarter full. This is to lower the
chance of triggering another overflow, which would be
wasteful. Subsequent calls will continue progress.
*/
static int redarken_chunk(char* heap_chunk, struct mark_stack* stk) {
value* p = Chunk_redarken_start(heap_chunk);
value* end = Chunk_redarken_end(heap_chunk);
while (p <= end) {
header_t hd = Hd_op(p);
if( Is_black_hd(hd) && Tag_hd(hd) < No_scan_tag ) {
if( stk->count < stk->size/4 ) {
mark_stack_push(stk, Val_op(p), 0, NULL);
} else {
/* Only fill up a quarter of the mark stack, we can resume later
for more if we need to */
Chunk_redarken_start(heap_chunk) = p;
return 0;
}
}
p += Whsize_hp(Hp_op(p));
}
Chunk_redarken_start(heap_chunk) =
(value*)(heap_chunk + Chunk_size(heap_chunk));
Chunk_redarken_end(heap_chunk) = 0;
return 1;
}
static void start_cycle (void)
{
CAMLassert (caml_gc_phase == Phase_idle);
CAMLassert (Caml_state->mark_stack->count == 0);
CAMLassert (redarken_first_chunk == NULL);
caml_gc_message (0x01, "Starting new major GC cycle\n");
caml_darken_all_roots_start ();
caml_gc_phase = Phase_mark;
caml_gc_subphase = Subphase_mark_roots;
ephe_list_pure = 1;
ephes_checked_if_pure = &caml_ephe_list_head;
ephes_to_check = &caml_ephe_list_head;
#ifdef DEBUG
++ major_gc_counter;
caml_heap_check ();
#endif
}
static void init_sweep_phase(void)
{
/* Phase_clean is done. */
/* Initialise the sweep phase. */
caml_gc_sweep_hp = caml_heap_start;
caml_fl_init_merge ();
caml_gc_phase = Phase_sweep;
sweep_chunk = caml_heap_start;
caml_gc_sweep_hp = sweep_chunk;
sweep_limit = sweep_chunk + Chunk_size (sweep_chunk);
caml_fl_wsz_at_phase_change = caml_fl_cur_wsz;
if (caml_major_gc_hook) (*caml_major_gc_hook)();
}
/* auxiliary function of mark_slice */
Caml_inline void mark_slice_darken(struct mark_stack* stk, value v, mlsize_t i,
int in_ephemeron, int *slice_pointers,
intnat *work)
{
value child;
header_t chd;
child = Field (v, i);
#ifdef NO_NAKED_POINTERS
if (Is_block (child) && ! Is_young (child)) {
#else
if (Is_block (child) && Is_in_heap (child)) {
#endif
CAML_EVENTLOG_DO (++ *slice_pointers);
chd = Hd_val (child);
if (Tag_hd (chd) == Forward_tag){
value f = Forward_val (child);
if ((in_ephemeron && Is_long(f)) ||
(Is_block (f)
&& (!Is_in_value_area(f) || Tag_val (f) == Forward_tag
|| Tag_val (f) == Lazy_tag
#ifdef FLAT_FLOAT_ARRAY
|| Tag_val (f) == Double_tag
#endif
))){
/* Do not short-circuit the pointer. */
}else{
/* The variable child is not changed because it must be mark alive */
Field (v, i) = f;
if (Is_block (f) && Is_young (f) && !Is_young (child)){
if(in_ephemeron) {
add_to_ephe_ref_table (Caml_state->ephe_ref_table, v, i);
} else {
add_to_ref_table (Caml_state->ref_table, &Field (v, i));
}
}
}
}
else if (Tag_hd(chd) == Infix_tag) {
child -= Infix_offset_val(child);
chd = Hd_val(child);
}
#ifdef NO_NAKED_POINTERS
/* See [caml_darken] for a description of this assertion. */
CAMLassert (Is_in_heap (child) || Is_black_hd (chd));
#endif
if (Is_white_hd (chd)){
ephe_list_pure = 0;
Hd_val (child) = Blackhd_hd (chd);
if( Tag_hd(chd) < No_scan_tag ) {
mark_stack_push(stk, child, 0, work);
} else {
*work -= 1; /* Account for header */
}
}
}
#if defined(NAKED_POINTERS_CHECKER) && defined(NATIVE_CODE)
else if (Is_block(child) && ! Is_young(child)) {
is_naked_pointer_safe(child, &Field (v, i));
}
#endif
}
static void mark_ephe_aux (struct mark_stack *stk, intnat *work,
int *slice_pointers)
{
value v, data, key;
header_t hd;
mlsize_t size, i;
v = *ephes_to_check;
hd = Hd_val(v);
CAMLassert(Tag_val (v) == Abstract_tag);
data = Field(v,CAML_EPHE_DATA_OFFSET);
if ( data != caml_ephe_none &&
Is_block (data) &&
#ifdef NO_NAKED_POINTERS
!Is_young(data) &&
#else
Is_in_heap (data) &&
#endif
Is_white_val (data)){
int alive_data = 1;
/* The liveness of the ephemeron is one of the condition */
if (Is_white_hd (hd)) alive_data = 0;
/* The liveness of the keys not caml_ephe_none is the other condition */
size = Wosize_hd (hd);
for (i = CAML_EPHE_FIRST_KEY; alive_data && i < size; i++){
key = Field (v, i);
ephemeron_again:
if (key != caml_ephe_none &&
Is_block (key) &&
#ifdef NO_NAKED_POINTERS
!Is_young(key)
#else
Is_in_heap(key)
#endif
){
if (Tag_val (key) == Forward_tag){
value f = Forward_val (key);
if (Is_long (f) ||
(Is_block (f) &&
(!Is_in_value_area(f) || Tag_val (f) == Forward_tag
|| Tag_val (f) == Lazy_tag
#ifdef FLAT_FLOAT_ARRAY
|| Tag_val (f) == Double_tag
#endif
))){
/* Do not short-circuit the pointer. */
}else{
Field (v, i) = key = f;
goto ephemeron_again;
}
}
if (Is_white_val (key)){
alive_data = 0;
}
}
}
*work -= Whsize_wosize(i);
if (alive_data){
mark_slice_darken(stk, v, CAML_EPHE_DATA_OFFSET, /*in_ephemeron=*/1,
slice_pointers, work);
} else { /* not triggered move to the next one */
ephes_to_check = &Field(v,CAML_EPHE_LINK_OFFSET);
return;
}
} else { /* a simily weak pointer or an already alive data */
*work -= 1;
}
/* all keys black or data none or black
move the ephemerons from (3) to the end of (1) */
if ( ephes_checked_if_pure == ephes_to_check ) {
/* corner case and optim */
ephes_checked_if_pure = &Field(v,CAML_EPHE_LINK_OFFSET);
ephes_to_check = ephes_checked_if_pure;
} else {
/* - remove v from the list (3) */
*ephes_to_check = Field(v,CAML_EPHE_LINK_OFFSET);
/* - insert it at the end of (1) */
Field(v,CAML_EPHE_LINK_OFFSET) = *ephes_checked_if_pure;
*ephes_checked_if_pure = v;
ephes_checked_if_pure = &Field(v,CAML_EPHE_LINK_OFFSET);
}
}
static void mark_slice (intnat work)
{
mark_entry me = {0, 0};
mlsize_t me_end = 0;
#ifdef CAML_INSTR
int slice_fields = 0; /** eventlog counters */
#endif /*CAML_INSTR*/
int slice_pointers = 0;
struct mark_stack* stk = Caml_state->mark_stack;
caml_gc_message (0x40, "Marking %"ARCH_INTNAT_PRINTF_FORMAT"d words\n", work);
caml_gc_message (0x40, "Subphase = %d\n", caml_gc_subphase);
while (1){
int can_mark = 0;
if (me.offset == me_end) {
if (stk->count > 0)
{
me = stk->stack[--stk->count];
me_end = Wosize_val(me.block);
can_mark = 1;
}
} else {
can_mark = 1;
}
if (work <= 0) {
if( can_mark ) {
mark_stack_push(stk, me.block, me.offset, NULL);
CAML_EVENTLOG_DO({
CAML_EV_COUNTER(EV_C_MAJOR_MARK_SLICE_REMAIN, me_end - me.offset);
});
}
break;
}
if( can_mark ) {
CAMLassert(Is_block(me.block) &&
Is_black_val (me.block) &&
Tag_val(me.block) < No_scan_tag);
mark_slice_darken(stk, me.block, me.offset++, /*in_ephemeron=*/ 0,
&slice_pointers, &work);
work--;
CAML_EVENTLOG_DO({
slice_fields++;
});
if( me.offset == me_end ) {
work--; /* Include header word */
}
} else if( redarken_first_chunk != NULL ) {
/* There are chunks that need to be redarkened because we
overflowed our mark stack */
if( redarken_chunk(redarken_first_chunk, stk) ) {
redarken_first_chunk = Chunk_next(redarken_first_chunk);
}
} else if (caml_gc_subphase == Subphase_mark_roots) {
CAML_EV_BEGIN(EV_MAJOR_MARK_ROOTS);
work = caml_darken_all_roots_slice (work);
CAML_EV_END(EV_MAJOR_MARK_ROOTS);
if (work > 0){
caml_gc_subphase = Subphase_mark_main;
}
} else if (*ephes_to_check != (value) NULL) {
/* Continue to scan the list of ephe */
mark_ephe_aux(stk,&work,&slice_pointers);
} else if (!ephe_list_pure){
/* We must scan again the list because some value have been darken */
ephe_list_pure = 1;
ephes_to_check = ephes_checked_if_pure;
}else{
switch (caml_gc_subphase){
case Subphase_mark_main: {
/* Subphase_mark_main is done.
Mark finalised values. */
CAML_EV_BEGIN(EV_MAJOR_MARK_MAIN);
caml_final_update_mark_phase ();
/* Complete the marking */
ephes_to_check = ephes_checked_if_pure;
CAML_EV_END(EV_MAJOR_MARK_MAIN);
caml_gc_subphase = Subphase_mark_final;
}
break;
case Subphase_mark_final: {
/** The set of unreachable value will not change anymore for
this cycle. Start clean phase. */
CAML_EV_BEGIN(EV_MAJOR_MARK_FINAL);
caml_gc_phase = Phase_clean;
caml_final_update_clean_phase ();
caml_memprof_update_clean_phase ();
if (caml_ephe_list_head != (value) NULL){
/* Initialise the clean phase. */
ephes_to_check = &caml_ephe_list_head;
} else {
/* Initialise the sweep phase. */
init_sweep_phase();
}
work = 0;
CAML_EV_END(EV_MAJOR_MARK_FINAL);
}
break;
default: CAMLassert (0);
}
}
}
CAML_EV_COUNTER(EV_C_MAJOR_MARK_SLICE_FIELDS, slice_fields);
CAML_EV_COUNTER(EV_C_MAJOR_MARK_SLICE_POINTERS, slice_pointers);
}
/* Clean ephemerons */
static void clean_slice (intnat work)
{
value v;
caml_gc_message (0x40, "Cleaning %"
ARCH_INTNAT_PRINTF_FORMAT "d words\n", work);
while (work > 0){
v = *ephes_to_check;
if (v != (value) NULL){
if (Is_white_val (v)){
/* The whole array is dead, remove it from the list. */
*ephes_to_check = Field (v, CAML_EPHE_LINK_OFFSET);
work -= 1;
}else{
caml_ephe_clean(v);
ephes_to_check = &Field (v, CAML_EPHE_LINK_OFFSET);
work -= Whsize_val (v);
}
}else{ /* End of list reached */
/* Phase_clean is done. */
/* Initialise the sweep phase. */
init_sweep_phase();
work = 0;
}
}
}
static void sweep_slice (intnat work)
{
char *hp;
header_t hd;
caml_gc_message (0x40, "Sweeping %"
ARCH_INTNAT_PRINTF_FORMAT "d words\n", work);
while (work > 0){
if (caml_gc_sweep_hp < sweep_limit){
hp = caml_gc_sweep_hp;
hd = Hd_hp (hp);
work -= Whsize_hd (hd);
caml_gc_sweep_hp += Bhsize_hd (hd);
switch (Color_hd (hd)){
case Caml_white:
caml_gc_sweep_hp =
(char *)caml_fl_merge_block(Val_hp (hp), sweep_limit);
break;
case Caml_blue:
/* Only the blocks of the free-list are blue. See [freelist.c]. */
caml_fl_merge = (value) Bp_hp (hp);
break;
default: /* gray or black */
CAMLassert (Color_hd (hd) == Caml_black);
Hd_hp (hp) = Whitehd_hd (hd);
break;
}
CAMLassert (caml_gc_sweep_hp <= sweep_limit);
}else{
sweep_chunk = Chunk_next (sweep_chunk);
if (sweep_chunk == NULL){
/* Sweeping is done. */
++ Caml_state->stat_major_collections;
work = 0;
caml_gc_phase = Phase_idle;
caml_request_minor_gc ();
}else{
caml_gc_sweep_hp = sweep_chunk;
sweep_limit = sweep_chunk + Chunk_size (sweep_chunk);
}
}
}
}
/* The main entry point for the major GC. Called about once for each
minor GC. [howmuch] is the amount of work to do:
-1 if the GC is triggered automatically
0 to let the GC compute the amount of work
[n] to make the GC do enough work to (on average) free [n] words
*/
void caml_major_collection_slice (intnat howmuch)
{
double p, dp, filt_p, spend;
intnat computed_work;
int i;
/*
Free memory at the start of the GC cycle (garbage + free list) (assumed):
FM = Caml_state->stat_heap_wsz * caml_percent_free
/ (100 + caml_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 cycle
(still assuming steady state).
Proportion of G consumed since the previous slice:
PH = caml_allocated_words / G
= caml_allocated_words * 3 * (100 + caml_percent_free)
/ (2 * Caml_state->stat_heap_wsz * caml_percent_free)
Proportion of extra-heap resources consumed since the previous slice:
PE = caml_extra_heap_resources
Proportion of total work to do in this slice:
P = max (PH, PE)
Here, we insert a time-based filter on the P variable to avoid large
latency spikes in the GC, so the P below is a smoothed-out version of
the P above.
Amount of marking work for the GC cycle:
MW = Caml_state->stat_heap_wsz * 100 / (100 + caml_percent_free)
+ caml_incremental_roots_count
Amount of sweeping work for the GC cycle:
SW = Caml_state->stat_heap_wsz
In order to finish marking with a non-empty free list, we will
use 40% of the time for marking, and 60% for sweeping.
Let MT be the time spent marking, ST the time spent sweeping, and TT
the total time for this cycle. We have:
MT = 40/100 * TT
ST = 60/100 * TT
Amount of time to spend on this slice:
T = P * TT = P * MT / (40/100) = P * ST / (60/100)
Since we must do MW work in MT time or SW work in ST time, the amount
of work for this slice is:
MS = P * MW / (40/100) if marking
SS = P * SW / (60/100) if sweeping
Amount of marking work for a marking slice:
MS = P * MW / (40/100)
MS = P * (Caml_state->stat_heap_wsz * 250
/ (100 + caml_percent_free)
+ 2.5 * caml_incremental_roots_count)
Amount of sweeping work for a sweeping slice:
SS = P * SW / (60/100)
SS = P * Caml_state->stat_heap_wsz * 5 / 3
This slice will either mark MS words or sweep SS words.
*/
if (caml_major_slice_begin_hook != NULL) (*caml_major_slice_begin_hook) ();
p = (double) caml_allocated_words * 3.0 * (100 + caml_percent_free)
/ Caml_state->stat_heap_wsz / caml_percent_free / 2.0;
if (caml_dependent_size > 0){
dp = (double) caml_dependent_allocated * (100 + caml_percent_free)
/ caml_dependent_size / caml_percent_free;
}else{
dp = 0.0;
}
if (p < dp) p = dp;
if (p < caml_extra_heap_resources) p = caml_extra_heap_resources;
p += p_backlog;
p_backlog = 0.0;
if (p > 0.3){
p_backlog = p - 0.3;
p = 0.3;
}
CAML_EV_COUNTER (EV_C_MAJOR_WORK_EXTRA,
(uintnat) (caml_extra_heap_resources * 1000000));
caml_gc_message (0x40, "ordered work = %"
ARCH_INTNAT_PRINTF_FORMAT "d words\n", howmuch);
caml_gc_message (0x40, "allocated_words = %"
ARCH_INTNAT_PRINTF_FORMAT "u\n",
caml_allocated_words);
caml_gc_message (0x40, "extra_heap_resources = %"
ARCH_INTNAT_PRINTF_FORMAT "uu\n",
(uintnat) (caml_extra_heap_resources * 1000000));
caml_gc_message (0x40, "raw work-to-do = %"
ARCH_INTNAT_PRINTF_FORMAT "du\n",
(intnat) (p * 1000000));
caml_gc_message (0x40, "work backlog = %"
ARCH_INTNAT_PRINTF_FORMAT "du\n",
(intnat) (p_backlog * 1000000));
for (i = 0; i < caml_major_window; i++){
caml_major_ring[i] += p / caml_major_window;
}
if (caml_gc_clock >= 1.0){
caml_gc_clock -= 1.0;
++caml_major_ring_index;
if (caml_major_ring_index >= caml_major_window){
caml_major_ring_index = 0;
}
}
if (howmuch == -1){
/* auto-triggered GC slice: spend work credit on the current bucket,
then do the remaining work, if any */
/* Note that the minor GC guarantees that the major slice is called in
automatic mode (with [howmuch] = -1) at least once per clock tick.
This means we never leave a non-empty bucket behind. */
spend = fmin (caml_major_work_credit,
caml_major_ring[caml_major_ring_index]);
caml_major_work_credit -= spend;
filt_p = caml_major_ring[caml_major_ring_index] - spend;
caml_major_ring[caml_major_ring_index] = 0.0;
}else{
/* forced GC slice: do work and add it to the credit */
if (howmuch == 0){
/* automatic setting: size of next bucket
we do not use the current bucket, as it may be empty */
int i = caml_major_ring_index + 1;
if (i >= caml_major_window) i = 0;
filt_p = caml_major_ring[i];
}else{
/* manual setting */
filt_p = (double) howmuch * 3.0 * (100 + caml_percent_free)
/ Caml_state->stat_heap_wsz / caml_percent_free / 2.0;
}
caml_major_work_credit += filt_p;
/* Limit work credit to 1.0 */
caml_major_work_credit = fmin(caml_major_work_credit, 1.0);
}
p = filt_p;
caml_gc_message (0x40, "filtered work-to-do = %"
ARCH_INTNAT_PRINTF_FORMAT "du\n",
(intnat) (p * 1000000));
if (caml_gc_phase == Phase_idle){
if (Caml_state->young_ptr == Caml_state->young_alloc_end){
/* We can only start a major GC cycle if the minor allocation arena
is empty, otherwise we'd have to treat it as a set of roots. */
CAML_EV_BEGIN(EV_MAJOR_ROOTS);
start_cycle ();
CAML_EV_END(EV_MAJOR_ROOTS);
}
p = 0;
goto finished;
}
if (p < 0){
p = 0;
goto finished;
}
if (caml_gc_phase == Phase_mark || caml_gc_phase == Phase_clean){
computed_work = (intnat) (p * ((double) Caml_state->stat_heap_wsz * 250
/ (100 + caml_percent_free)
+ caml_incremental_roots_count));
}else{
computed_work = (intnat) (p * Caml_state->stat_heap_wsz * 5 / 3);
}
caml_gc_message (0x40, "computed work = %"
ARCH_INTNAT_PRINTF_FORMAT "d words\n", computed_work);
if (caml_gc_phase == Phase_mark){
CAML_EV_COUNTER (EV_C_MAJOR_WORK_MARK, computed_work);
CAML_EV_BEGIN(EV_MAJOR_MARK);
mark_slice (computed_work);
CAML_EV_END(EV_MAJOR_MARK);
caml_gc_message (0x02, "!");
}else if (caml_gc_phase == Phase_clean){
clean_slice (computed_work);
caml_gc_message (0x02, "%%");
}else{
CAMLassert (caml_gc_phase == Phase_sweep);
CAML_EV_COUNTER (EV_C_MAJOR_WORK_SWEEP, computed_work);
CAML_EV_BEGIN(EV_MAJOR_SWEEP);
sweep_slice (computed_work);
CAML_EV_END(EV_MAJOR_SWEEP);
caml_gc_message (0x02, "$");
}
if (caml_gc_phase == Phase_idle){
CAML_EV_BEGIN(EV_MAJOR_CHECK_AND_COMPACT);
caml_compact_heap_maybe ();
CAML_EV_END(EV_MAJOR_CHECK_AND_COMPACT);
}
finished:
caml_gc_message (0x40, "work-done = %"
ARCH_INTNAT_PRINTF_FORMAT "du\n",
(intnat) (p * 1000000));
/* if some of the work was not done, take it back from the credit
or spread it over the buckets. */
p = filt_p - p;
spend = fmin (p, caml_major_work_credit);
caml_major_work_credit -= spend;
if (p > spend){
p -= spend;
p /= caml_major_window;
for (i = 0; i < caml_major_window; i++) caml_major_ring[i] += p;
}
Caml_state->stat_major_words += caml_allocated_words;
caml_allocated_words = 0;
caml_dependent_allocated = 0;
caml_extra_heap_resources = 0.0;
if (caml_major_slice_end_hook != NULL) (*caml_major_slice_end_hook) ();
}
/* This does not call [caml_compact_heap_maybe] because the estimates of
free and live memory are only valid for a cycle done incrementally.
Besides, this function itself is called by [caml_compact_heap_maybe].
*/
void caml_finish_major_cycle (void)
{
if (caml_gc_phase == Phase_idle){
p_backlog = 0.0; /* full major GC cycle, the backlog becomes irrelevant */
start_cycle ();
}
while (caml_gc_phase == Phase_mark) mark_slice (LONG_MAX);
while (caml_gc_phase == Phase_clean) clean_slice (LONG_MAX);
CAMLassert (caml_gc_phase == Phase_sweep);
CAMLassert (redarken_first_chunk == NULL);
while (caml_gc_phase == Phase_sweep) sweep_slice (LONG_MAX);
CAMLassert (caml_gc_phase == Phase_idle);
Caml_state->stat_major_words += caml_allocated_words;
caml_allocated_words = 0;
}
/* Call this function to make sure [bsz] is greater than or equal
to both [Heap_chunk_min] and the current heap increment.
*/
asize_t caml_clip_heap_chunk_wsz (asize_t wsz)
{
asize_t result = wsz;
uintnat incr;
/* Compute the heap increment as a word size. */
if (caml_major_heap_increment > 1000){
incr = caml_major_heap_increment;
}else{
incr = Caml_state->stat_heap_wsz / 100 * caml_major_heap_increment;