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avoid changing mark bits for old objects

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For a minor GC and pages that contain backpointers,
leave mark bits as they are; instead make a pass to
shift mark bits for new objects to "dead" bits, and
use dead bits for fixup.

This change is intended as a small step toward incremental
collection.
This commit is contained in:
Matthew Flatt 2015-10-13 12:44:20 -06:00
parent 6b93b18a1a
commit 7db0c3b1d4
2 changed files with 145 additions and 118 deletions
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259
racket/src/racket/gc2/newgc.c
View File

@ -4211,7 +4211,6 @@ static void mark_backpointers(NewGC *gc)
if (work->size_class == SIZE_CLASS_BIG_PAGE) {
/* must be a big page */
work->size_class = SIZE_CLASS_BIG_PAGE_MARKED;
push_ptr(gc, TAG_AS_BIG_PAGE_PTR(BIG_PAGE_TO_OBJECT(work)));
gc->memory_in_use -= work->size;
} else if (work->size_class == SIZE_CLASS_SMALL_PAGE) {
@ -4223,13 +4222,10 @@ static void mark_backpointers(NewGC *gc)
while (start < end) {
objhead *info = (objhead *)start;
if (!info->dead) {
info->mark = 1;
if (!info->dead)
push_ptr(gc, OBJHEAD_TO_OBJPTR(start));
}
start += info->size;
}
work->scan_boundary = PREFIX_SIZE;
gc->memory_in_use -= work->size;
} else {
/* medium page */
@ -4240,10 +4236,8 @@ static void mark_backpointers(NewGC *gc)
while (start <= end) {
objhead *info = (objhead *)start;
if (!info->dead) {
info->mark = 1;
if (!info->dead)
push_ptr(gc, OBJHEAD_TO_OBJPTR(info));
}
start += info->size;
}
@ -4407,58 +4401,6 @@ inline static void do_heap_compact(NewGC *gc)
}
}
static int repair_mixed_page(NewGC *gc, mpage *page, void **end, int need_fixup)
{
void **start = PPTR(NUM(page->addr) + PREFIX_SIZE);
Fixup2_Proc *fixup_table = gc->fixup_table;
int non_dead = 0;
while (start <= end) {
objhead *info = (objhead *)start;
if (info->mark) {
if (need_fixup) {
switch(info->type) {
case PAGE_ARRAY:
{
void **tempend = PPTR(info) + info->size, **tmpstart;
tmpstart = OBJHEAD_TO_OBJPTR(start);
while (tmpstart < tempend) gcFIXUP2(*tmpstart++, gc);
}
break;
case PAGE_TAGGED:
{
void *obj_start = OBJHEAD_TO_OBJPTR(start);
unsigned short tag = *(unsigned short *)obj_start;
ASSERT_TAG(tag);
fixup_table[tag](obj_start, gc);
}
break;
case PAGE_ATOMIC:
break;
case PAGE_PAIR:
{
Scheme_Object *p = (Scheme_Object *)OBJHEAD_TO_OBJPTR(start);
gcFIXUP2(SCHEME_CAR(p), gc);
gcFIXUP2(SCHEME_CDR(p), gc);
}
break;
default:
printf("Unhandled info->type %i\n", info->type);
abort();
}
}
start += info->size;
info->mark = 0;
non_dead++;
} else {
info->dead = 1;
start += info->size;
}
}
return non_dead;
}
static void chain_marked_on(NewGC *gc)
/* add any page that is marked on to the `modified_next` chain; this
is needed for a master GC, because the place GCs do not register
@ -4536,7 +4478,111 @@ static void chain_marked_on_check(NewGC *gc)
static void chain_marked_on_check(NewGC *gc) { }
#endif
static void unmark_range(void **start, void **end)
{
while(start < end) {
objhead *info = (objhead *)start;
if (info->mark)
info->mark = 0;
else
info->dead = 1;
start += info->size;
}
}
static void unmark_heap(NewGC *gc)
/* Set `dead` bit if not `mark`, otherwise clean `mark`. After this
pass, objects are live if `dead` is not set. */
{
mpage *page;
/* See start of repair_heap() for more information on the current
page state. */
for (page = gc->modified_next; page; page = page->modified_next) {
GC_ASSERT(page->marked_on || page->marked_from);
if (page->generation == AGE_VACATED) {
/* this page will be released later */
} else {
if (page->size_class >= SIZE_CLASS_BIG_PAGE) {
page->size_class = SIZE_CLASS_BIG_PAGE; /* remove the mark, if any */
} else if (page->size_class == SIZE_CLASS_SMALL_PAGE) {
GCDEBUG((DEBUGOUTF, "Unmarking objs on page %p, starting with %p\n",
page, start));
unmark_range(PPTR(NUM(page->addr) + page->scan_boundary),
PAGE_END_VSS(page));
/* repair phase should walk the full page: */
page->scan_boundary = PREFIX_SIZE;
} else {
GC_ASSERT(page->size_class == SIZE_CLASS_MED_PAGE);
if ((page->generation == AGE_GEN_0) || gc->gc_full)
unmark_range(PPTR(NUM(page->addr) + PREFIX_SIZE),
PPTR(NUM(page->addr) + APAGE_SIZE - page->obj_size));
}
}
}
/* All gen-half pages count as modified: */
for (page = gc->gen_half.pages; page; page = page->next) {
GC_ASSERT(page->generation == AGE_GEN_HALF);
unmark_range(PPTR(NUM(page->addr) + PREFIX_SIZE),
PPTR(NUM(page->addr) + page->size - 1));
}
}
static int repair_mixed_page(NewGC *gc, mpage *page, void **end, int need_fixup)
{
void **start = PPTR(NUM(page->addr) + PREFIX_SIZE);
Fixup2_Proc *fixup_table = gc->fixup_table;
int non_dead = 0;
while (start <= end) {
objhead *info = (objhead *)start;
if (!info->dead) {
non_dead++;
if (need_fixup) {
switch(info->type) {
case PAGE_ARRAY:
{
void **tempend = PPTR(info) + info->size, **tmpstart;
tmpstart = OBJHEAD_TO_OBJPTR(start);
while (tmpstart < tempend) gcFIXUP2(*tmpstart++, gc);
}
break;
case PAGE_TAGGED:
{
void *obj_start = OBJHEAD_TO_OBJPTR(start);
unsigned short tag = *(unsigned short *)obj_start;
ASSERT_TAG(tag);
fixup_table[tag](obj_start, gc);
}
break;
case PAGE_ATOMIC:
break;
case PAGE_PAIR:
{
Scheme_Object *p = (Scheme_Object *)OBJHEAD_TO_OBJPTR(start);
gcFIXUP2(SCHEME_CAR(p), gc);
gcFIXUP2(SCHEME_CDR(p), gc);
}
break;
default:
printf("Unhandled info->type %i\n", info->type);
abort();
}
}
}
start += info->size;
}
return non_dead;
}
static void repair_heap(NewGC *gc)
/* not dead => fixup pointers */
{
uintptr_t memory_in_use;
mpage *page, *next;
@ -4577,7 +4623,6 @@ static void repair_heap(NewGC *gc)
GCDEBUG((DEBUGOUTF, "Cleaning objs on page %p, starting with %p\n",
page, start));
page->size_class = SIZE_CLASS_BIG_PAGE; /* remove the mark */
if (need_fixup) {
switch(page->page_type) {
case PAGE_TAGGED:
@ -4599,71 +4644,52 @@ static void repair_heap(NewGC *gc)
memory_in_use += page->size;
} else if (page->size_class == SIZE_CLASS_SMALL_PAGE) {
void **start = PPTR(NUM(page->addr) + page->scan_boundary);
void **end = PAGE_END_VSS(page);
if (need_fixup) {
void **start = PPTR(NUM(page->addr) + page->scan_boundary);
void **end = PAGE_END_VSS(page);
GCDEBUG((DEBUGOUTF, "Cleaning objs on page %p, starting with %p\n",
page, start));
switch(page->page_type) {
case PAGE_TAGGED:
while(start < end) {
objhead *info = (objhead *)start;
GCDEBUG((DEBUGOUTF, "Cleaning objs on page %p, starting with %p\n",
page, start));
switch(page->page_type) {
case PAGE_TAGGED:
while(start < end) {
objhead *info = (objhead *)start;
if(info->mark) {
void *obj_start = OBJHEAD_TO_OBJPTR(start);
unsigned short tag = *(unsigned short *)obj_start;
ASSERT_TAG(tag);
info->mark = 0;
if (need_fixup)
if(!info->dead) {
void *obj_start = OBJHEAD_TO_OBJPTR(start);
unsigned short tag = *(unsigned short *)obj_start;
ASSERT_TAG(tag);
fixup_table[tag](obj_start, gc);
} else
info->dead = 1;
start += info->size;
}
break;
case PAGE_ATOMIC:
while(start < end) {
objhead *info = (objhead *)start;
if(info->mark)
info->mark = 0;
else
info->dead = 1;
start += info->size;
}
break;
case PAGE_ARRAY:
while(start < end) {
objhead *info = (objhead *)start;
size_t size = info->size;
if(info->mark) {
void **tempend = PPTR(info) + info->size;
if (need_fixup) {
}
start += info->size;
}
break;
case PAGE_ATOMIC:
break;
case PAGE_ARRAY:
while(start < end) {
objhead *info = (objhead *)start;
size_t size = info->size;
if(!info->dead) {
void **tempend = PPTR(info) + info->size;
start = OBJHEAD_TO_OBJPTR(start);
while(start < tempend) gcFIXUP2(*start++, gc);
} else
start = tempend;
info->mark = 0;
} else {
info->dead = 1;
start += size;
} else {
start += size;
}
}
}
break;
case PAGE_PAIR:
while(start < end) {
objhead *info = (objhead *)start;
if(info->mark) {
if (need_fixup) {
break;
case PAGE_PAIR:
while(start < end) {
objhead *info = (objhead *)start;
if(!info->dead) {
Scheme_Object *p = (Scheme_Object *)OBJHEAD_TO_OBJPTR(start);
gcFIXUP2(SCHEME_CAR(p), gc);
gcFIXUP2(SCHEME_CDR(p), gc);
}
info->mark = 0;
} else
info->dead = 1;
start += PAIR_SIZE_IN_BYTES >> LOG_WORD_SIZE;
start += PAIR_SIZE_IN_BYTES >> LOG_WORD_SIZE;
}
break;
}
break;
}
page->scan_boundary = page->size;
@ -5149,6 +5175,7 @@ static void garbage_collect(NewGC *gc, int force_full, int no_full, int switchin
chain_marked_on(gc);
else if (gc->gc_full)
chain_marked_on_check(gc);
unmark_heap(gc);
repair_heap(gc);
TIME_STEP("repaired");
clean_up_heap(gc);

4
racket/src/racket/gc2/newgc.h
View File

@ -35,8 +35,8 @@ typedef struct mpage {
uintptr_t alloc_size; /* for a nursery: total size of the nursery */
uintptr_t med_search_start; /* medium page: offset for searching for a free slot */
uintptr_t scan_boundary; /* small gen1 page: during GC, boundary between objects that can be
left alone and that that will be scanned & fixed up; objects before
have cleared "mark" bits, while objects after (may) have "mark" bits sets */
should be treated as previously gen1 and objects that should be
treated as just moved from gen0 */
};
unsigned short live_size; /* except for big pages, total size of live objects on the page */
unsigned char generation :2;