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Performance fix: Lower operations and function calls by checking for zone_address before doing expensive memory reads #767

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Performance fix: Lower operations and function calls by checking for zone_address before doing expensive memory reads #767

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67 changes: 38 additions & 29 deletions src/allocator.c
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Original file line number Diff line number Diff line change
Expand Up @@ -534,23 +534,22 @@ _dispatch_alloc_maybe_madvise_page(dispatch_continuation_t c)
volatile bitmap_t *page_bitmaps;
get_maps_and_indices_for_continuation((dispatch_continuation_t)page, NULL,
NULL, (bitmap_t **)&page_bitmaps, NULL);
unsigned int i;
for (i = 0; i < BITMAPS_PER_PAGE; i++) {
if (page_bitmaps[i] != 0) {
unsigned int last_locked;
for (last_locked = 0; last_locked < BITMAPS_PER_PAGE; last_locked++) {
if (page_bitmaps[last_locked] != 0) {
return;
}
}
// They are all unallocated, so we could madvise the page. Try to
// take ownership of them all.
int last_locked = 0;
do {
for (last_locked = 0; last_locked < BITMAPS_PER_PAGE; last_locked++) {
if (!os_atomic_cmpxchg(&page_bitmaps[last_locked], BITMAP_C(0),
BITMAP_ALL_ONES, relaxed)) {
// We didn't get one; since there is a cont allocated in
// the page, we can't madvise. Give up and unlock all.
goto unlock;
}
} while (++last_locked < (signed)BITMAPS_PER_PAGE);
}
#if DISPATCH_DEBUG
//fprintf(stderr, "%s: madvised page %p for cont %p (next = %p), "
// "[%u+1]=%u bitmaps at %p\n", __func__, page, c, c->do_next,
Expand All @@ -563,10 +562,10 @@ _dispatch_alloc_maybe_madvise_page(dispatch_continuation_t c)
MADV_FREE));

unlock:
while (last_locked > 1) {
page_bitmaps[--last_locked] = BITMAP_C(0);
}
if (last_locked) {
while (last_locked > 1) {
page_bitmaps[--last_locked] = BITMAP_C(0);
}
os_atomic_store(&page_bitmaps[0], BITMAP_C(0), relaxed);
}
return;
Expand Down Expand Up @@ -654,27 +653,37 @@ _dispatch_allocator_enumerate(task_t remote_task,
vm_address_t zone_address, memory_reader_t reader,
void (^recorder)(vm_address_t, void *, size_t, bool *stop))
{
const size_t heap_size = remote_dal->dal_magazine_size;
const size_t dc_size = remote_dal->dal_allocation_size;
const size_t dc_flags_offset = remote_dal->dal_allocation_isa_offset;
bool stop = false;
void *heap;

while (zone_address) {
// FIXME: improve this by not faulting everything and driving it through
// the bitmap.
kern_return_t kr = reader(remote_task, zone_address, heap_size, &heap);
size_t offs = remote_dal->dal_first_allocation_offset;
if (kr) return kr;
while (offs < heap_size) {
void *isa = *(void **)(heap + offs + dc_flags_offset);
if (isa && isa != remote_dal->dal_deferred_free_isa) {
recorder(zone_address + offs, heap + offs, dc_size, &stop);
if (stop) return KERN_SUCCESS;
if (zone_address)
{
const size_t heap_size = remote_dal->dal_magazine_size;
const size_t dc_size = remote_dal->dal_allocation_size;
const size_t dc_flags_offset = remote_dal->dal_allocation_isa_offset;
bool stop = false;
void *heap = NULL;

do
{
// FIXME: improve this by not faulting everything and driving it through
// the bitmap.
kern_return_t kr;
size_t offs;

kr = reader(remote_task, zone_address, heap_size, &heap);
if (kr)
return kr;

for (offs = remote_dal->dal_first_allocation_offset; offs < heap_size; offs += dc_size)
{
void *isa = *(void **)(heap + offs + dc_flags_offset);
if (isa && isa != remote_dal->dal_deferred_free_isa)
{
recorder(zone_address + offs, heap + offs, dc_size, &stop);
if (stop)
return KERN_SUCCESS;
}
}
offs += dc_size;
}
zone_address = (vm_address_t)((dispatch_heap_t)heap)->header.dh_next;
zone_address = (vm_address_t)((dispatch_heap_t)heap)->header.dh_next;
} while (zone_address);
}

return KERN_SUCCESS;
Expand Down