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shared_heap.c
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shared_heap.c
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/**************************************************************************/
/* */
/* OCaml */
/* */
/* KC Sivaramakrishnan, Indian Institute of Technology, Madras */
/* Stephen Dolan, University of Cambridge */
/* */
/* Copyright 2015 Indian Institute of Technology, Madras */
/* Copyright 2015 University of Cambridge */
/* */
/* 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 <stdlib.h>
#include <string.h>
#include <assert.h>
#include "caml/addrmap.h"
#include "caml/custom.h"
#include "caml/runtime_events.h"
#include "caml/fail.h"
#include "caml/fiber.h" /* for verification */
#include "caml/gc.h"
#include "caml/globroots.h"
#include "caml/major_gc.h"
#include "caml/memory.h"
#include "caml/mlvalues.h"
#include "caml/platform.h"
#include "caml/roots.h"
#include "caml/shared_heap.h"
#include "caml/sizeclasses.h"
#include "caml/startup_aux.h"
#include "caml/weak.h"
CAMLexport atomic_uintnat caml_compactions_count;
typedef unsigned int sizeclass;
/* Initial MARKED, UNMARKED, and GARBAGE values; any permutation would work */
struct global_heap_state caml_global_heap_state = {
0 << HEADER_COLOR_SHIFT,
1 << HEADER_COLOR_SHIFT,
2 << HEADER_COLOR_SHIFT,
};
typedef struct pool {
struct pool* next;
value* next_obj;
caml_domain_state* owner;
sizeclass sz;
} pool;
static_assert(sizeof(pool) == Bsize_wsize(POOL_HEADER_WSIZE), "");
#define POOL_SLAB_WOFFSET(sz) (POOL_HEADER_WSIZE + wastage_sizeclass[sz])
#define POOL_FIRST_BLOCK(p, sz) ((header_t*)(p) + POOL_SLAB_WOFFSET(sz))
#define POOL_END(p) ((header_t*)(p) + POOL_WSIZE)
#define POOL_BLOCKS(p) ((POOL_WSIZE - POOL_HEADER_WSIZE) / \
wsize_sizeclass[(p)->sz])
typedef struct large_alloc {
caml_domain_state* owner;
struct large_alloc* next;
} large_alloc;
static_assert(sizeof(large_alloc) % sizeof(value) == 0, "");
#define LARGE_ALLOC_HEADER_SZ sizeof(large_alloc)
static struct {
caml_plat_mutex lock;
pool* free;
/* these only contain swept memory of terminated domains*/
struct heap_stats stats;
_Atomic(pool*) global_avail_pools[NUM_SIZECLASSES];
_Atomic(pool*) global_full_pools[NUM_SIZECLASSES];
large_alloc* global_large;
} pool_freelist = {
CAML_PLAT_MUTEX_INITIALIZER,
NULL,
{ 0, },
{ NULL, },
{ NULL, },
NULL
};
/* readable and writable only by the current thread */
struct caml_heap_state {
pool* avail_pools[NUM_SIZECLASSES];
pool* full_pools[NUM_SIZECLASSES];
pool* unswept_avail_pools[NUM_SIZECLASSES];
pool* unswept_full_pools[NUM_SIZECLASSES];
large_alloc* swept_large;
large_alloc* unswept_large;
sizeclass next_to_sweep;
caml_domain_state* owner;
struct heap_stats stats;
};
struct compact_pool_stat {
int free_blocks;
int live_blocks;
};
/* You need to hold the [pool_freelist] lock to call these functions. */
static void orphan_heap_stats_with_lock(struct caml_heap_state *);
static void adopt_pool_stats_with_lock(struct caml_heap_state *,
pool *, sizeclass);
struct caml_heap_state* caml_init_shared_heap (void) {
int i;
struct caml_heap_state* heap;
heap = caml_stat_alloc_noexc(sizeof(struct caml_heap_state));
if(heap != NULL) {
for (i = 0; i<NUM_SIZECLASSES; i++) {
heap->avail_pools[i] = heap->full_pools[i] =
heap->unswept_avail_pools[i] = heap->unswept_full_pools[i] = 0;
}
heap->next_to_sweep = 0;
heap->swept_large = NULL;
heap->unswept_large = NULL;
heap->owner = Caml_state;
memset(&heap->stats, 0, sizeof(heap->stats));
}
return heap;
}
static int move_all_pools(pool** src, _Atomic(pool*)* dst,
caml_domain_state* new_owner) {
int count = 0;
while (*src) {
pool* p = *src;
*src = p->next;
p->owner = new_owner;
p->next = *dst;
*dst = p;
count++;
}
return count;
}
void caml_teardown_shared_heap(struct caml_heap_state* heap) {
int i;
int released = 0, released_large = 0;
caml_plat_lock(&pool_freelist.lock);
for (i = 0; i < NUM_SIZECLASSES; i++) {
released +=
move_all_pools(&heap->avail_pools[i],
&pool_freelist.global_avail_pools[i], NULL);
released +=
move_all_pools(&heap->full_pools[i],
&pool_freelist.global_full_pools[i], NULL);
/* should be swept by now */
CAMLassert(!heap->unswept_avail_pools[i]);
CAMLassert(!heap->unswept_full_pools[i]);
}
CAMLassert(!heap->unswept_large);
while (heap->swept_large) {
large_alloc* a = heap->swept_large;
heap->swept_large = a->next;
a->next = pool_freelist.global_large;
pool_freelist.global_large = a;
released_large++;
}
orphan_heap_stats_with_lock(heap);
caml_plat_unlock(&pool_freelist.lock);
caml_stat_free(heap);
caml_gc_log("Shutdown shared heap. Released %d active pools, %d large",
released, released_large);
}
/* Allocating and deallocating pools from the global freelist. */
static pool* pool_acquire(struct caml_heap_state* local) {
pool* r;
caml_plat_lock(&pool_freelist.lock);
if (!pool_freelist.free) {
void* mem = caml_mem_map(Bsize_wsize(POOL_WSIZE), 0);
if (mem) {
CAMLassert(pool_freelist.free == NULL);
r = (pool*)mem;
r->next = pool_freelist.free;
r->owner = NULL;
pool_freelist.free = r;
}
}
r = pool_freelist.free;
if (r)
pool_freelist.free = r->next;
caml_plat_unlock(&pool_freelist.lock);
if (r) CAMLassert (r->owner == NULL);
return r;
}
/* release [pool] to the current free list of pools */
static void pool_release(struct caml_heap_state* local,
pool* pool,
sizeclass sz)
{
pool->owner = NULL;
CAMLassert(pool->sz == sz);
local->stats.pool_words -= POOL_WSIZE;
local->stats.pool_frag_words -= POOL_HEADER_WSIZE + wastage_sizeclass[sz];
caml_plat_lock(&pool_freelist.lock);
pool->next = pool_freelist.free;
pool_freelist.free = pool;
caml_plat_unlock(&pool_freelist.lock);
}
/* free the memory of [pool], giving it back to the OS */
static void pool_free(struct caml_heap_state* local,
pool* pool,
sizeclass sz)
{
CAMLassert(pool->sz == sz);
local->stats.pool_words -= POOL_WSIZE;
local->stats.pool_frag_words -= POOL_HEADER_WSIZE + wastage_sizeclass[sz];
caml_mem_unmap(pool, Bsize_wsize(POOL_WSIZE));
}
static void calc_pool_stats(pool* a, sizeclass sz, struct heap_stats* s)
{
header_t* p = POOL_FIRST_BLOCK(a, sz);
header_t* end = POOL_END(a);
mlsize_t wh = wsize_sizeclass[sz];
s->pool_frag_words += POOL_SLAB_WOFFSET(sz);
while (p + wh <= end) {
header_t hd = (header_t)atomic_load_relaxed((atomic_uintnat*)p);
if (hd) {
s->pool_live_words += Whsize_hd(hd);
s->pool_frag_words += wh - Whsize_hd(hd);
s->pool_live_blocks++;
}
p += wh;
}
CAMLassert(end == p);
s->pool_words += POOL_WSIZE;
}
/* Initialize a pool and its object freelist */
Caml_inline void pool_initialize(pool* r,
sizeclass sz,
caml_domain_state* owner)
{
mlsize_t wh = wsize_sizeclass[sz];
header_t* p = POOL_FIRST_BLOCK(r, sz);
header_t* end = POOL_END(r);
r->next = 0;
r->owner = owner;
r->next_obj = 0;
r->sz = sz;
p[0] = 0;
p[1] = 0;
p += wh;
while (p + wh <= end) {
p[0] = 0; /* zero header indicates free object */
p[1] = (value)(p - wh);
#ifdef DEBUG
for (int w = 2 ; w < wh; w++) {
p[w] = Debug_free_major;
}
#endif
p += wh;
}
CAMLassert(p == end);
CAMLassert((uintptr_t)end % Cache_line_bsize == 0);
r->next_obj = (value*)(p - wh);
}
/* Allocating an object from a pool */
CAMLno_tsan_for_perf
static intnat pool_sweep(struct caml_heap_state* local,
pool**,
sizeclass sz ,
int release_to_global_pool);
/* Adopt pool from the pool_freelist avail and full pools
to satisfy an allocation */
static pool* pool_global_adopt(struct caml_heap_state* local, sizeclass sz)
{
pool* r = NULL;
int adopted_pool = 0;
/* probably no available pools out there to be had */
if( !atomic_load_relaxed(&pool_freelist.global_avail_pools[sz]) &&
!atomic_load_relaxed(&pool_freelist.global_full_pools[sz]) )
return NULL;
/* Haven't managed to find a pool locally, try the global ones */
caml_plat_lock(&pool_freelist.lock);
if( atomic_load_relaxed(&pool_freelist.global_avail_pools[sz]) ) {
r = atomic_load_relaxed(&pool_freelist.global_avail_pools[sz]);
if( r ) {
atomic_store_relaxed(&pool_freelist.global_avail_pools[sz], r->next);
r->next = 0;
local->avail_pools[sz] = r;
adopt_pool_stats_with_lock(local, r, sz);
#ifdef DEBUG
{
value* next_obj = r->next_obj;
while( next_obj ) {
CAMLassert(next_obj[0] == 0);
next_obj = (value*)next_obj[1];
}
}
#endif
}
}
/* There were no global avail pools, so let's adopt one of the full ones and
try our luck sweeping it later on */
if( !r ) {
r = atomic_load_relaxed(&pool_freelist.global_full_pools[sz]);
if( r ) {
atomic_store_relaxed(&pool_freelist.global_full_pools[sz], r->next);
r->next = local->full_pools[sz];
local->full_pools[sz] = r;
adopt_pool_stats_with_lock(local, r, sz);
adopted_pool = 1;
r = 0; // this pool is full
}
}
caml_plat_unlock(&pool_freelist.lock);
if( !r && adopted_pool ) {
Caml_state->major_work_done_between_slices +=
pool_sweep(local, &local->full_pools[sz], sz, 0);
r = local->avail_pools[sz];
}
return r;
}
/* Allocating an object from a pool */
static pool* pool_find(struct caml_heap_state* local, sizeclass sz) {
pool* r;
/* Hopefully we have a pool we can use directly */
r = local->avail_pools[sz];
if (r) return r;
/* Otherwise, try to sweep until we find one */
while (!local->avail_pools[sz] && local->unswept_avail_pools[sz]) {
Caml_state->major_work_done_between_slices +=
pool_sweep(local, &local->unswept_avail_pools[sz], sz, 0);
}
r = local->avail_pools[sz];
if (r) return r;
/* Haven't managed to find a pool locally, try the global ones */
r = pool_global_adopt(local, sz);
if (r) return r;
/* Failing that, we need to allocate a new pool */
r = pool_acquire(local);
if (!r) return 0; /* if we can't allocate, give up */
local->stats.pool_words += POOL_WSIZE;
if (local->stats.pool_words > local->stats.pool_max_words)
local->stats.pool_max_words = local->stats.pool_words;
local->stats.pool_frag_words += POOL_HEADER_WSIZE + wastage_sizeclass[sz];
/* Having allocated a new pool, set it up for size sz */
local->avail_pools[sz] = r;
pool_initialize(r, sz, local->owner);
return r;
}
static void* pool_allocate(struct caml_heap_state* local, sizeclass sz) {
value* p;
value* next;
pool* r = pool_find(local, sz);
if (!r) return 0;
p = r->next_obj;
next = (value*)p[1];
r->next_obj = next;
CAMLassert(p[0] == 0);
if (!next) {
local->avail_pools[sz] = r->next;
r->next = local->full_pools[sz];
local->full_pools[sz] = r;
}
CAMLassert(r->next_obj == 0 || *r->next_obj == 0);
return p;
}
static void* large_allocate(struct caml_heap_state* local, mlsize_t sz) {
large_alloc* a = malloc(sz + LARGE_ALLOC_HEADER_SZ);
if (!a) return NULL;
local->stats.large_words += Wsize_bsize(sz + LARGE_ALLOC_HEADER_SZ);
if (local->stats.large_words > local->stats.large_max_words)
local->stats.large_max_words = local->stats.large_words;
local->stats.large_blocks++;
a->owner = local->owner;
a->next = local->swept_large;
local->swept_large = a;
return (char*)a + LARGE_ALLOC_HEADER_SZ;
}
value* caml_shared_try_alloc(struct caml_heap_state* local, mlsize_t wosize,
tag_t tag, reserved_t reserved)
{
mlsize_t whsize = Whsize_wosize(wosize);
value* p;
uintnat colour;
CAMLassert (wosize > 0);
CAMLassert (tag != Infix_tag);
CAML_EV_ALLOC(wosize);
if (whsize <= SIZECLASS_MAX) {
struct heap_stats* s;
sizeclass sz = sizeclass_wsize[whsize];
CAMLassert(wsize_sizeclass[sz] >= whsize);
p = pool_allocate(local, sz);
if (!p) return 0;
s = &local->stats;
s->pool_live_blocks++;
s->pool_live_words += whsize;
s->pool_frag_words += wsize_sizeclass[sz] - whsize;
} else {
p = large_allocate(local, Bsize_wsize(whsize));
if (!p) return 0;
}
colour = caml_global_heap_state.MARKED;
Hd_hp (p) = Make_header_with_reserved(wosize, tag, colour, reserved);
/* Annotating a release barrier on `p` because TSan does not see the
* happens-before relationship established by address dependencies
* between the initializing writes here and the read in major_gc.c
* marking (#12894) */
CAML_TSAN_ANNOTATE_HAPPENS_BEFORE(p);
#ifdef DEBUG
{
int i;
for (i = 0; i < wosize; i++) {
Field(Val_hp(p), i) = Debug_free_major;
}
}
#endif
return p;
}
/* Sweeping */
static intnat pool_sweep(struct caml_heap_state* local, pool** plist,
sizeclass sz, int release_to_global_pool) {
intnat work = 0;
pool* a = *plist;
if (!a) return 0;
*plist = a->next;
{
header_t* p = POOL_FIRST_BLOCK(a, sz);
header_t* end = POOL_END(a);
mlsize_t wh = wsize_sizeclass[sz];
int all_used = 1;
struct heap_stats* s = &local->stats;
while (p + wh <= end) {
header_t hd = (header_t)atomic_load_relaxed((atomic_uintnat*)p);
if (hd == 0) {
/* already on freelist */
all_used = 0;
} else if (Has_status_hd(hd, caml_global_heap_state.GARBAGE)) {
CAMLassert(Whsize_hd(hd) <= wh);
if (Tag_hd (hd) == Custom_tag) {
void (*final_fun)(value) = Custom_ops_val(Val_hp(p))->finalize;
if (final_fun != NULL) final_fun(Val_hp(p));
}
/* add to freelist */
atomic_store_relaxed((atomic_uintnat*)p, 0);
p[1] = (value)a->next_obj;
CAMLassert(Is_block((value)p));
#ifdef DEBUG
{
int i;
mlsize_t wo = Wosize_whsize(wh);
for (i = 1; i < wo; i++) {
Field(Val_hp(p), i) = Debug_free_major;
}
}
#endif
a->next_obj = (value*)p;
all_used = 0;
/* update stats */
s->pool_live_blocks--;
s->pool_live_words -= Whsize_hd(hd);
local->owner->swept_words += Whsize_hd(hd);
s->pool_frag_words -= (wh - Whsize_hd(hd));
} else {
/* still live, the pool can't be released to the global freelist */
release_to_global_pool = 0;
}
p += wh;
work += wh;
}
if (release_to_global_pool) {
pool_release(local, a, sz);
} else {
pool** list = all_used ? &local->full_pools[sz] : &local->avail_pools[sz];
a->next = *list;
*list = a;
}
}
return work;
}
static intnat large_alloc_sweep(struct caml_heap_state* local) {
value* p;
header_t hd;
large_alloc* a = local->unswept_large;
if (!a) return 0;
local->unswept_large = a->next;
p = (value*)((char*)a + LARGE_ALLOC_HEADER_SZ);
/* The header being read here may be concurrently written by a thread doing
marking. This is fine because marking can only make UNMARKED objects
MARKED or NOT_MARKABLE, all of which are treated identically here. */
hd = Hd_hp(p);
if (Has_status_hd(hd, caml_global_heap_state.GARBAGE)) {
if (Tag_hd (hd) == Custom_tag) {
void (*final_fun)(value) = Custom_ops_val(Val_hp(p))->finalize;
if (final_fun != NULL) final_fun(Val_hp(p));
}
local->stats.large_words -=
Whsize_hd(hd) + Wsize_bsize(LARGE_ALLOC_HEADER_SZ);
local->owner->swept_words +=
Whsize_hd(hd) + Wsize_bsize(LARGE_ALLOC_HEADER_SZ);
local->stats.large_blocks--;
free(a);
} else {
a->next = local->swept_large;
local->swept_large = a;
}
return Whsize_hd(hd);
}
static void verify_swept(struct caml_heap_state*);
intnat caml_sweep(struct caml_heap_state* local, intnat work) {
/* Sweep local pools */
while (work > 0 && local->next_to_sweep < NUM_SIZECLASSES) {
sizeclass sz = local->next_to_sweep;
intnat full_sweep_work = 0;
intnat avail_sweep_work =
pool_sweep(local, &local->unswept_avail_pools[sz], sz, 1);
work -= avail_sweep_work;
if (work > 0) {
full_sweep_work = pool_sweep(local,
&local->unswept_full_pools[sz],
sz, 1);
work -= full_sweep_work;
}
if(full_sweep_work+avail_sweep_work == 0) {
local->next_to_sweep++;
}
}
/* Sweep global pools */
while (work > 0 && local->unswept_large) {
work -= large_alloc_sweep(local);
}
if (caml_params->verify_heap && work > 0) {
/* sweeping is complete, check everything worked */
verify_swept(local);
}
return work;
}
uintnat caml_heap_size(struct caml_heap_state* local) {
return Bsize_wsize(local->stats.pool_words + local->stats.large_words);
}
uintnat caml_top_heap_words(struct caml_heap_state* local) {
/* FIXME: summing two maximums computed at different points in time
returns an incorrect result. */
return local->stats.pool_max_words + local->stats.large_max_words;
}
uintnat caml_heap_blocks(struct caml_heap_state* local) {
return local->stats.pool_live_blocks + local->stats.large_blocks;
}
void caml_redarken_pool(struct pool* r, scanning_action f, void* fdata) {
mlsize_t wh = wsize_sizeclass[r->sz];
header_t* p = POOL_FIRST_BLOCK(r, r->sz);
header_t* end = POOL_END(r);
while (p + wh <= end) {
header_t hd = p[0];
if (hd != 0 && Has_status_hd(hd, caml_global_heap_state.MARKED)) {
f(fdata, Val_hp(p), 0);
}
p += wh;
}
}
/* Heap and freelist stats */
/* Move the given heap stats to the orphan pools.
You need to hold the [pool_freelist] lock. */
static void orphan_heap_stats_with_lock(struct caml_heap_state *heap) {
caml_accum_heap_stats(&pool_freelist.stats, &heap->stats);
memset(&heap->stats, 0, sizeof(heap->stats));
}
/* The stats for an adopted pool are moved from the free pool stats to
the heap stats of the adopting domain.
You need to hold the [pool_freelist] lock. */
static void adopt_pool_stats_with_lock(
struct caml_heap_state* adopter, pool *r, sizeclass sz)
{
struct heap_stats pool_stats = { 0, };
calc_pool_stats(r, sz, &pool_stats);
caml_accum_heap_stats(&adopter->stats, &pool_stats);
caml_remove_heap_stats(&pool_freelist.stats, &pool_stats);
}
/* Move the stats of all orphan pools into the given heap.
You need to hold the [pool_freelist] lock. */
static void adopt_all_pool_stats_with_lock(struct caml_heap_state *adopter) {
caml_accum_heap_stats(&adopter->stats, &pool_freelist.stats);
memset(&pool_freelist.stats, 0, sizeof(pool_freelist.stats));
}
void caml_collect_heap_stats_sample(
struct caml_heap_state* local,
struct heap_stats* sample)
{
*sample = local->stats;
}
/* Add the orphan pool stats to a stats accumulator. */
void caml_accum_orphan_heap_stats(struct heap_stats* acc)
{
caml_plat_lock(&pool_freelist.lock);
caml_accum_heap_stats(acc, &pool_freelist.stats);
caml_plat_unlock(&pool_freelist.lock);
}
/* Atoms */
static const header_t atoms[256] = {
#define A(i) Make_header(0, i, NOT_MARKABLE)
A(0),A(1),A(2),A(3),A(4),A(5),A(6),A(7),A(8),A(9),A(10),
A(11),A(12),A(13),A(14),A(15),A(16),A(17),A(18),A(19),A(20),
A(21),A(22),A(23),A(24),A(25),A(26),A(27),A(28),A(29),A(30),
A(31),A(32),A(33),A(34),A(35),A(36),A(37),A(38),A(39),A(40),
A(41),A(42),A(43),A(44),A(45),A(46),A(47),A(48),A(49),A(50),
A(51),A(52),A(53),A(54),A(55),A(56),A(57),A(58),A(59),A(60),
A(61),A(62),A(63),A(64),A(65),A(66),A(67),A(68),A(69),A(70),
A(71),A(72),A(73),A(74),A(75),A(76),A(77),A(78),A(79),A(80),
A(81),A(82),A(83),A(84),A(85),A(86),A(87),A(88),A(89),A(90),
A(91),A(92),A(93),A(94),A(95),A(96),A(97),A(98),A(99),A(100),
A(101),A(102),A(103),A(104),A(105),A(106),A(107),A(108),A(109),
A(110),A(111),A(112),A(113),A(114),A(115),A(116),A(117),A(118),
A(119),A(120),A(121),A(122),A(123),A(124),A(125),A(126),A(127),
A(128),A(129),A(130),A(131),A(132),A(133),A(134),A(135),A(136),
A(137),A(138),A(139),A(140),A(141),A(142),A(143),A(144),A(145),
A(146),A(147),A(148),A(149),A(150),A(151),A(152),A(153),A(154),
A(155),A(156),A(157),A(158),A(159),A(160),A(161),A(162),A(163),
A(164),A(165),A(166),A(167),A(168),A(169),A(170),A(171),A(172),
A(173),A(174),A(175),A(176),A(177),A(178),A(179),A(180),A(181),
A(182),A(183),A(184),A(185),A(186),A(187),A(188),A(189),A(190),
A(191),A(192),A(193),A(194),A(195),A(196),A(197),A(198),A(199),
A(200),A(201),A(202),A(203),A(204),A(205),A(206),A(207),A(208),
A(209),A(210),A(211),A(212),A(213),A(214),A(215),A(216),A(217),
A(218),A(219),A(220),A(221),A(222),A(223),A(224),A(225),A(226),
A(227),A(228),A(229),A(230),A(231),A(232),A(233),A(234),A(235),
A(236),A(237),A(238),A(239),A(240),A(241),A(242),A(243),A(244),
A(245),A(246),A(247),A(248),A(249),A(250),A(251),A(252),A(253),
A(254),A(255)
#undef A
};
CAMLexport value caml_atom(tag_t tag) {
return Val_hp(&atoms[tag]);
}
void caml_init_major_heap (asize_t size) {
}
/* Verify heap invariants.
Verification happens just after the heap is cycled during STW, so
everything should be unmarked. If something reachable marked after
cycling the heap, it means that garbage was reachable beforehand.
*/
struct heap_verify_state {
value* stack;
int stack_len;
int sp;
intnat objs;
struct addrmap seen;
};
struct heap_verify_state* caml_verify_begin (void)
{
struct heap_verify_state init = {0, 0, 0, 0, ADDRMAP_INIT};
struct heap_verify_state* st = caml_stat_alloc(sizeof init);
*st = init;
return st;
}
static void verify_push (void* st_v, value v, volatile value* ignored)
{
struct heap_verify_state* st = st_v;
if (!Is_block(v)) return;
if (st->sp == st->stack_len) {
st->stack_len = st->stack_len * 2 + 100;
st->stack = caml_stat_resize(st->stack,
sizeof(value*) * st->stack_len);
}
st->stack[st->sp++] = v;
}
void caml_verify_root(void* state, value v, volatile value* p)
{
verify_push(state, v, p);
}
static scanning_action_flags verify_scanning_flags = 0;
static void verify_object(struct heap_verify_state* st, value v) {
intnat* entry;
if (!Is_block(v)) return;
CAMLassert (!Is_young(v));
CAMLassert (Hd_val(v));
if (Tag_val(v) == Infix_tag) {
v -= Infix_offset_val(v);
CAMLassert(Tag_val(v) == Closure_tag);
}
entry = caml_addrmap_insert_pos(&st->seen, v);
if (*entry != ADDRMAP_NOT_PRESENT) return;
*entry = 1;
if (Has_status_val(v, NOT_MARKABLE)) return;
st->objs++;
CAMLassert(Has_status_val(v, caml_global_heap_state.UNMARKED));
if (Tag_val(v) == Cont_tag) {
struct stack_info* stk = Ptr_val(Field(v, 0));
if (stk != NULL)
caml_scan_stack(verify_push, verify_scanning_flags, st, stk, 0);
} else if (Tag_val(v) < No_scan_tag) {
int i = 0;
if (Tag_val(v) == Closure_tag) {
i = Start_env_closinfo(Closinfo_val(v));
}
for (; i < Wosize_val(v); i++) {
value f = Field(v, i);
if (Is_block(f)) verify_push(st, f, Op_val(v)+i);
}
}
}
void caml_verify_heap_from_stw(caml_domain_state *domain) {
struct heap_verify_state* st = caml_verify_begin();
caml_do_roots (&caml_verify_root, verify_scanning_flags, st, domain, 1);
caml_scan_global_roots(&caml_verify_root, st);
while (st->sp) verify_object(st, st->stack[--st->sp]);
caml_addrmap_clear(&st->seen);
caml_stat_free(st->stack);
caml_stat_free(st);
}
/* Compaction starts here. See [caml_compact_heap] for entry. */
/* Given a single value `v`, found at `p`, check if it points to an
evacuated block, and if so update it using the forwarding pointer
created by the compactor. */
static inline void compact_update_value(void* ignored,
value v,
volatile value* p)
{
if (Is_block(v)) {
CAMLassert(!Is_young(v));
tag_t tag = Tag_val(v);
int infix_offset = 0;
if (tag == Infix_tag) {
infix_offset = Infix_offset_val(v);
/* v currently points to an Infix_tag inside of a Closure_tag.
The forwarding pointer we want is in the first field of the
Closure_tag. */
v -= infix_offset;
CAMLassert(Tag_val(v) == Closure_tag);
}
/* non-markable blocks can't move */
if (Has_status_val(v, NOT_MARKABLE))
return;
if (Whsize_val(v) <= SIZECLASS_MAX) {
/* MARKED header status means the location `p` points to a block that
has been evacuated. Use the forwarding pointer in the first field
to update to the new location. */
if (Has_status_val(v, caml_global_heap_state.MARKED)) {
value fwd = Field(v, 0) + infix_offset;
CAMLassert(Is_block(fwd));
CAMLassert(Tag_val(fwd) == tag);
*p = fwd;
}
}
}
}
/* Given a value found at `p` check if it points to an evacuated
block, and if so update it using the forwarding pointer created by
the compactor. */
static inline void compact_update_value_at(volatile value* p)
{
compact_update_value(NULL, *p, p);
}
/* For each pointer in the block pointed to by `p`, check if it points
to an evacuated block and if so update it using the forwarding
pointer created by the compactor. */
static void compact_update_block(header_t* p)
{
header_t hd = Hd_hp(p);
/* We should never be called with a block that has a zero header (this would
indicate a bug in traversing the shared pools). */
CAMLassert(hd != 0);
tag_t tag = Tag_hd(hd);
/* We should never encounter an Infix tag iterating over the shared pools or
large allocations. We could find it in roots but those use
[compact_update_value]. */
CAMLassert(tag != Infix_tag);
if (tag == Cont_tag) {
value stk = Field(Val_hp(p), 0);
if (Ptr_val(stk)) {
caml_scan_stack(&compact_update_value, 0, NULL, Ptr_val(stk), 0);
}
} else {
uintnat offset = 0;
if (tag == Closure_tag) {
offset = Start_env_closinfo(Closinfo_val(Val_hp(p)));
}
if (tag < No_scan_tag) {
mlsize_t wosz = Wosize_hd(hd);
for (mlsize_t i = offset; i < wosz; i++) {
compact_update_value_at(&Field(Val_hp(p), i));
}
}
}
}
/* Update all the live blocks in a list of pools. */
static void compact_update_pools(pool *cur_pool)
{
while (cur_pool) {
header_t* p = POOL_FIRST_BLOCK(cur_pool, cur_pool->sz);
header_t* end = POOL_END(cur_pool);
mlsize_t wh = wsize_sizeclass[cur_pool->sz];
while (p + wh <= end) {
if (*p &&
Has_status_val(Val_hp(p), caml_global_heap_state.UNMARKED)) {
compact_update_block(p);
}
p += wh;
}
cur_pool = cur_pool->next;
}
}
/* Update all the fields in the list of ephemerons found at `*ephe_p` */
static void compact_update_ephe_list(volatile value *ephe_p)
{
while (*ephe_p) {
compact_update_value_at(ephe_p);
value ephe = *ephe_p;
mlsize_t wosize = Wosize_val(ephe);
compact_update_value_at(&Field(ephe, CAML_EPHE_DATA_OFFSET));
for (int i = CAML_EPHE_FIRST_KEY ; i < wosize ; i++) {
compact_update_value_at(&Field(ephe, i));
}
ephe_p = &Field(ephe, CAML_EPHE_LINK_OFFSET);
}
}
/* Compact the heap for the given domain. Run in parallel for all domains. */
void caml_compact_heap(caml_domain_state* domain_state,
int participating_count,
caml_domain_state** participants)
{
caml_gc_log("Compacting heap start");
CAML_EV_BEGIN(EV_COMPACT);
/* Warning: caml_compact_heap must only be called from
[cycle_all_domains_callback] in major_gc.c as there are
very specific conditions the compaction algorithm expects.
The following code implements a compaction algorithm that is similar to
Edward's Two-Finger algorithm from the original 1974 LISP book (The
Programming Language LISP). At a high level the algorithm works as a series
of parallel (using all running domains) phases separated by global barriers:
1. For each size class
a. Compute the number of live blocks in partially filled pools
b. Keep enough pools to fully contain the number of live blocks and
set the rest to be evacuated
c. For each live block in each pool in the evacuation list,
allocate and copy into a non-evacuating pool.
2. Proceed through the roots and the heap, updating pointers to evacuated
blocks to point to the new location of the block. Update finalisers and
ephemerons too.
3. Go through pools evacuated and release them. Finally free all but
one pool in the freelist.
4. One domain needs to release the pools in the freelist back to the OS.
The algorithm requires one full pass through the whole heap (pools and large
allocations) to rewrite pointers, as well as two passes through the
partially-occupied pools in the heap to compute the number of live blocks
and evacuate them.
*/
/* First phase. Here we compute the number of live blocks in partially
filled pools, determine pools to be evacuated and then evacuate from them.
For the first phase we need not consider full pools, they
cannot be evacuated to or from. */
caml_global_barrier();
CAML_EV_BEGIN(EV_COMPACT_EVACUATE);
struct caml_heap_state* heap = Caml_state->shared_heap;
#ifdef DEBUG
/* Check preconditions for the heap: */
for (int sz_class = 1; sz_class < NUM_SIZECLASSES; sz_class++) {
/* No sweeping has happened yet */
CAMLassert(heap->avail_pools[sz_class] == NULL);
CAMLassert(heap->full_pools[sz_class] == NULL);
CAMLassert(heap->swept_large == NULL);
/* No pools waiting for adoption */
if (participants[0] == Caml_state) {
CAMLassert(
atomic_load_relaxed(&pool_freelist.global_avail_pools[sz_class]) ==
NULL);
CAMLassert(