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Make ephemeron marking incremental.
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Without incremental marking of ephemerons, with sufficiently large
ephemeron list, the GC would fail to make progress as it would start
scanning the ephemeron list from the beginning every time.
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@kayceesrk
kayceesrk committed Sep 10, 2018
1 parent 0c5690c commit df76040
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Showing 5 changed files with 78 additions and 42 deletions.
4 changes: 1 addition & 3 deletions byterun/caml/domain_state.tbl
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Original file line number Diff line number Diff line change
Expand Up @@ -14,9 +14,7 @@ DOMAIN_STATE(uintnat, stealing)
DOMAIN_STATE(uintnat, allocated_words)
DOMAIN_STATE(uintnat, swept_words)
DOMAIN_STATE(struct caml__roots_block*, local_roots)
DOMAIN_STATE(value, ephe_list_todo)
DOMAIN_STATE(value, ephe_list_live)
DOMAIN_STATE(uintnat, ephe_cycle)
DOMAIN_STATE(struct caml_ephe_info*, ephe_info)
DOMAIN_STATE(struct caml_final_info*, final_info)
DOMAIN_STATE(intnat, backtrace_pos)
DOMAIN_STATE(intnat, backtrace_active)
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11 changes: 11 additions & 0 deletions byterun/caml/weak.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,16 @@

extern value caml_ephe_none;

struct caml_ephe_info {
value todo;
value live;
uintnat cycle;
struct {
value* todop;
uintnat cycle;
} cursor;
};

#define CAML_EPHE_LINK_OFFSET 0
#define CAML_EPHE_DOMAIN_OFFSET 1
#define CAML_EPHE_DATA_OFFSET 2
Expand All @@ -40,6 +50,7 @@ extern value caml_ephe_none;
#define Ephe_domain(e) (*(struct domain**)(Op_val(e) + CAML_EPHE_DOMAIN_OFFSET))
#define Ephe_data(e) (*(Op_val(e) + CAML_EPHE_DATA_OFFSET))

struct caml_ephe_info* caml_alloc_ephe_info (void);
void caml_ephe_clean(struct domain* d, value e);
value caml_bias_ephe_list(value, struct domain*);

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18 changes: 9 additions & 9 deletions byterun/domain.c
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Original file line number Diff line number Diff line change
Expand Up @@ -791,19 +791,19 @@ static void handover_ephemerons(caml_domain_state* domain_state)
value todo_tail = 0;
value live_tail = 0;

if (domain_state->ephe_list_todo == 0 &&
domain_state->ephe_list_live == 0)
if (domain_state->ephe_info->todo == 0 &&
domain_state->ephe_info->live == 0)
return;

todo_tail = caml_bias_ephe_list(domain_state->ephe_list_todo, (struct domain*)NULL);
live_tail = caml_bias_ephe_list(domain_state->ephe_list_live, (struct domain*)NULL);
caml_add_orphaned_ephe(domain_state->ephe_list_todo, todo_tail,
domain_state->ephe_list_live, live_tail);
if (domain_state->ephe_list_todo != 0) {
todo_tail = caml_bias_ephe_list(domain_state->ephe_info->todo, (struct domain*)NULL);
live_tail = caml_bias_ephe_list(domain_state->ephe_info->live, (struct domain*)NULL);
caml_add_orphaned_ephe(domain_state->ephe_info->todo, todo_tail,
domain_state->ephe_info->live, live_tail);
if (domain_state->ephe_info->todo != 0) {
caml_ephe_todo_list_emptied();
}
domain_state->ephe_list_live = 0;
domain_state->ephe_list_todo = 0;
domain_state->ephe_info->live = 0;
domain_state->ephe_info->todo = 0;
}

static void handover_finalisers(caml_domain_state* domain_state)
Expand Down
75 changes: 47 additions & 28 deletions byterun/major_gc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ extern value caml_ephe_none; /* See weak.c */
struct ephe_cycle_info_t {
atomic_uintnat num_domains_todo;
/* Number of domains that need to scan their ephemerons in the current major
* GC cycle. This field is decremented when ephe_list_todo at a domain
* GC cycle. This field is decremented when ephe_info->todo list at a domain
* becomes empty. */
atomic_uintnat ephe_cycle;
/* Ephemeron cycle count */
Expand Down Expand Up @@ -127,7 +127,7 @@ static void record_ephe_marking_done (uintnat ephe_cycle)

caml_plat_lock(&ephe_lock);
if (ephe_cycle == ephe_cycle_info.ephe_cycle.val) {
Caml_state->ephe_cycle = ephe_cycle;
Caml_state->ephe_info->cycle = ephe_cycle;
ephe_cycle_info.num_domains_done.val++;
}
caml_plat_unlock(&ephe_lock);
Expand Down Expand Up @@ -208,18 +208,18 @@ void caml_adopt_orphaned_work ()

if (orph_structs.ephe_list_live) {
last = caml_bias_ephe_list(orph_structs.ephe_list_live, d);
Ephe_link(last) = domain_state->ephe_list_live;
domain_state->ephe_list_live = orph_structs.ephe_list_live;
Ephe_link(last) = domain_state->ephe_info->live;
domain_state->ephe_info->live = orph_structs.ephe_list_live;
orph_structs.ephe_list_live = 0;
}

if (orph_structs.ephe_list_todo) {
if (domain_state->ephe_list_todo == 0) {
if (domain_state->ephe_info->todo == 0) {
caml_ephe_todo_list_stolen();
}
last = caml_bias_ephe_list(orph_structs.ephe_list_todo, d);
Ephe_link(last) = domain_state->ephe_list_todo;
domain_state->ephe_list_todo = orph_structs.ephe_list_todo;
Ephe_link(last) = domain_state->ephe_info->todo;
domain_state->ephe_info->todo = orph_structs.ephe_list_todo;
orph_structs.ephe_list_todo = 0;
}

Expand Down Expand Up @@ -610,17 +610,23 @@ void caml_darken(void* state, value v, value* ignored) {
}
}

intnat ephe_mark (intnat budget)
intnat ephe_mark (intnat budget, uintnat for_cycle)
{
value v, data, key, f, todo;
value* prev_linkp;
header_t hd;
mlsize_t size, i;
caml_domain_state* domain_state = Caml_state;
int alive_data;
intnat marked = 0, made_live = 0;

todo = domain_state->ephe_list_todo;
prev_linkp = &domain_state->ephe_list_todo;
if (domain_state->ephe_info->cursor.cycle == for_cycle) {
prev_linkp = domain_state->ephe_info->cursor.todop;
todo = *prev_linkp;
} else {
todo = domain_state->ephe_info->todo;
prev_linkp = &domain_state->ephe_info->todo;
}
while (todo != 0 && budget > 0) {
v = todo;
todo = Ephe_link(v);
Expand Down Expand Up @@ -659,15 +665,25 @@ intnat ephe_mark (intnat budget)
if (data != caml_ephe_none && Is_block(data) && is_unmarked(data)) {
caml_darken (0, data, 0);
}
Ephe_link(v) = domain_state->ephe_list_live;
domain_state->ephe_list_live = v;
Ephe_link(v) = domain_state->ephe_info->live;
domain_state->ephe_info->live = v;
*prev_linkp = todo;
made_live++;
} else {
/* Leave this ephemeron on the todo list */
prev_linkp = &Ephe_link(v);
}
marked++;
}

caml_gc_log ("Mark Ephemeron: %s. for ephemeron cycle=%"ARCH_INTNAT_PRINTF_FORMAT"d "
"marked=%"ARCH_INTNAT_PRINTF_FORMAT"d made_live=%"ARCH_INTNAT_PRINTF_FORMAT"d",
domain_state->ephe_info->cursor.cycle == for_cycle ? "continued from cursor" : "discarded cursor",
for_cycle, marked, made_live);

domain_state->ephe_info->cursor.cycle = for_cycle;
domain_state->ephe_info->cursor.todop = prev_linkp;

return budget;
}

Expand All @@ -677,18 +693,18 @@ intnat ephe_sweep (struct domain* d, intnat budget)
value v;
caml_domain_state* domain_state = d->state;

while (domain_state->ephe_list_todo != 0 && budget > 0) {
v = domain_state->ephe_list_todo;
domain_state->ephe_list_todo = Ephe_link(v);
while (domain_state->ephe_info->todo != 0 && budget > 0) {
v = domain_state->ephe_info->todo;
domain_state->ephe_info->todo = Ephe_link(v);
CAMLassert (Tag_val(v) == Abstract_tag);

if (is_unmarked(v)) {
/* The whole array is dead, drop this ephemeron */
budget -= 1;
} else {
caml_ephe_clean(d, v);
Ephe_link(v) = domain_state->ephe_list_live;
domain_state->ephe_list_live = v;
Ephe_link(v) = domain_state->ephe_info->live;
domain_state->ephe_info->live = v;
budget -= Whsize_val(v);
}
}
Expand Down Expand Up @@ -879,11 +895,13 @@ static void cycle_all_domains_callback(struct domain* domain, void* unused)
}

/* Ephemerons */
CAMLassert(domain->state->ephe_list_todo == (value) NULL);
domain->state->ephe_list_todo = domain->state->ephe_list_live;
domain->state->ephe_list_live = (value) NULL;
domain->state->ephe_cycle = 0;
if (domain->state->ephe_list_todo == (value) NULL)
CAMLassert(domain->state->ephe_info->todo == (value) NULL);
domain->state->ephe_info->todo = domain->state->ephe_info->live;
domain->state->ephe_info->live = (value) NULL;
domain->state->ephe_info->cycle = 0;
domain->state->ephe_info->cursor.todop = NULL;
domain->state->ephe_info->cursor.cycle = 0;
if (domain->state->ephe_info->todo == (value) NULL)
caml_ephe_todo_list_emptied();

/* Finalisers */
Expand Down Expand Up @@ -1055,24 +1073,24 @@ static intnat major_collection_slice(intnat howmuch,

/* Ephemerons */
saved_ephe_cycle = atomic_load_acq(&ephe_cycle_info.ephe_cycle);
if (domain_state->ephe_list_todo != (value) NULL &&
saved_ephe_cycle > domain_state->ephe_cycle) {
if (domain_state->ephe_info->todo != (value) NULL &&
saved_ephe_cycle > domain_state->ephe_info->cycle) {
caml_ev_begin("major_gc/ephe_mark");
budget = ephe_mark(budget);
budget = ephe_mark(budget, saved_ephe_cycle);
caml_ev_end("major_gc/ephe_mark");
if (domain_state->ephe_list_todo == (value) NULL)
if (domain_state->ephe_info->todo == (value) NULL)
caml_ephe_todo_list_emptied ();
else if (budget > 0 && domain_state->marking_done)
record_ephe_marking_done(saved_ephe_cycle);
else if (budget > 0) goto mark_again;
}

if (caml_gc_phase == Phase_sweep_ephe &&
domain_state->ephe_list_todo != 0) {
domain_state->ephe_info->todo != 0) {
caml_ev_begin("major_gc/ephe_sweep");
budget = ephe_sweep (d, budget);
caml_ev_end("major_gc/ephe_sweep");
if (domain_state->ephe_list_todo == 0) {
if (domain_state->ephe_info->todo == 0) {
atomic_fetch_add_verify_ge0(&num_domains_to_ephe_sweep, -1);
}
}
Expand Down Expand Up @@ -1347,6 +1365,7 @@ void caml_init_major_gc(caml_domain_state* d) {
d->stealing = 0;
/* Finalisers. Fresh domains participate in updating finalisers. */
d->final_info = caml_alloc_final_info ();
d->ephe_info = caml_alloc_ephe_info();
atomic_fetch_add(&num_domains_to_final_update_first, 1);
atomic_fetch_add(&num_domains_to_final_update_last, 1);
}
Expand Down
12 changes: 10 additions & 2 deletions byterun/weak.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,14 @@ value caml_ephe_none = (value)&caml_dummy[1];
#define None_val (Val_int(0))
#define Some_tag 0

struct caml_ephe_info* caml_alloc_ephe_info ()
{
struct caml_ephe_info* e =
caml_stat_alloc (sizeof(struct caml_ephe_info));
memset (e, 0, sizeof(struct caml_ephe_info));
return e;
}

/* [len] is a value that represents a number of words (fields) */
CAMLprim value caml_ephe_create (value len)
{
Expand All @@ -50,8 +58,8 @@ CAMLprim value caml_ephe_create (value len)
if (size < CAML_EPHE_FIRST_KEY || size > Max_wosize) caml_invalid_argument ("Weak.create");
res = caml_alloc_shr (size, Abstract_tag);

Ephe_link(res) = domain_state->ephe_list_live;
domain_state->ephe_list_live = res;
Ephe_link(res) = domain_state->ephe_info->live;
domain_state->ephe_info->live = res;
Ephe_domain(res) = caml_domain_self();
for (i = CAML_EPHE_DATA_OFFSET; i < size; i++)
Op_val(res)[i] = caml_ephe_none;
Expand Down

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