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Fix semispace page stealing

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Ensure number of stolen pages is even.  Avoid madvising on every
collection.  Cache the page size.
This commit is contained in:
Andy Wingo 2022-04-17 21:51:20 +02:00
parent 3315fc7477
commit 3f54fb3dbf
1 changed files with 39 additions and 22 deletions
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61
semi.h
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@ -11,6 +11,10 @@
struct semi_space {
uintptr_t hp;
uintptr_t limit;
uintptr_t from_space;
uintptr_t to_space;
size_t page_size;
size_t stolen_pages;
uintptr_t base;
size_t size;
long count;
@ -56,31 +60,38 @@ static void collect_for_alloc(struct mutator *mut, size_t bytes) NEVER_INLINE;
static void visit(void **loc, void *visit_data);
static int semi_space_steal_pages(struct semi_space *space, size_t npages) {
size_t page_size = getpagesize();
size_t stolen_pages = space->stolen_pages + npages;
size_t old_limit_size = space->limit - space->to_space;
size_t new_limit_size =
(space->size - align_up(stolen_pages, 2) * space->page_size) / 2;
if (npages & 1) npages++;
size_t half_size = (npages * page_size) >> 1;
if (space->limit - space->hp < half_size)
if (space->to_space + new_limit_size < space->hp)
return 0;
space->limit -= half_size;
size_t tospace_offset = space->limit - space->base;
madvise((void*)(space->base + tospace_offset), half_size, MADV_DONTNEED);
size_t fromspace_offset =
(tospace_offset + (space->size >> 1)) & (space->size - 1);
madvise((void*)(space->base + fromspace_offset), half_size, MADV_DONTNEED);
space->limit = space->to_space + new_limit_size;
space->stolen_pages = stolen_pages;
madvise((void*)(space->to_space + new_limit_size),
old_limit_size - new_limit_size,
MADV_DONTNEED);
madvise((void*)(space->from_space + new_limit_size),
old_limit_size - new_limit_size,
MADV_DONTNEED);
return 1;
}
static void semi_space_set_stolen_pages(struct semi_space *space, size_t npages) {
space->stolen_pages = npages;
size_t limit_size =
(space->size - align_up(npages, 2) * space->page_size) / 2;
space->limit = space->to_space + limit_size;
}
static void flip(struct semi_space *space) {
uintptr_t split = space->base + (space->size >> 1);
if (space->hp <= split) {
space->hp = split;
space->limit = space->base + space->size;
} else {
space->hp = space->base;
space->limit = split;
}
space->hp = space->from_space;
space->from_space = space->to_space;
space->to_space = space->hp;
space->limit = space->hp + space->size / 2;
space->count++;
}
@ -174,7 +185,7 @@ static void collect(struct mutator *mut) {
while(grey < semi->hp)
grey = scan(heap, grey);
large_object_space_finish_gc(large);
semi_space_steal_pages(semi, large->live_pages_at_last_collection);
semi_space_set_stolen_pages(semi, large->live_pages_at_last_collection);
// fprintf(stderr, "%zd bytes copied\n", (space->size>>1)-(space->limit-space->hp));
}
@ -255,6 +266,10 @@ static inline void* get_field(void **addr) {
}
static int initialize_semi_space(struct semi_space *space, size_t size) {
// Allocate even numbers of pages.
size_t page_size = getpagesize();
size = align_up(size, page_size * 2);
void *mem = mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
if (mem == MAP_FAILED) {
@ -262,10 +277,12 @@ static int initialize_semi_space(struct semi_space *space, size_t size) {
return 0;
}
space->hp = space->base = (uintptr_t) mem;
space->to_space = space->hp = space->base = (uintptr_t) mem;
space->from_space = space->base + size / 2;
space->page_size = page_size;
space->stolen_pages = 0;
space->size = size;
space->count = -1;
flip(space);
space->count = 0;
return 1;
}