/**
* 计算当前线程的本地分配缓冲区的新大小
*/
inline size_t ThreadLocalAllocBuffer::compute_size(size_t obj_size) {
const size_t aligned_obj_size = align_object_size(obj_size);
// Compute the size for the new TLAB.
// The "last" tlab may be smaller to reduce fragmentation.
// unsafe_max_tlab_alloc is just a hint.
const size_t available_size = Universe::heap()->unsafe_max_tlab_alloc(myThread()) / HeapWordSize;
size_t new_tlab_size = MIN2(available_size, desired_size() + aligned_obj_size);
// Make sure there's enough room for object and filler int[].
const size_t obj_plus_filler_size = aligned_obj_size + alignment_reserve();
if (new_tlab_size < obj_plus_filler_size) {
// If there isn't enough room for the allocation, return failure.
if (PrintTLAB && Verbose) {
gclog_or_tty->print_cr("ThreadLocalAllocBuffer::compute_size(" SIZE_FORMAT ")"
" returns failure",
obj_size);
}
return 0;
}
if (PrintTLAB && Verbose) {
gclog_or_tty->print_cr("ThreadLocalAllocBuffer::compute_size(" SIZE_FORMAT ")"
" returns " SIZE_FORMAT,
obj_size, new_tlab_size);
}
return new_tlab_size;
}
/**
* 根据统计信息调整当前线程的本地分配缓冲区的基准大小
*/
void ThreadLocalAllocBuffer::resize() {
if (ResizeTLAB) { //允许调整线程的本地分配缓冲区大小
// Compute the next tlab size using expected allocation amount
size_t alloc = (size_t)(_allocation_fraction.average() *
(Universe::heap()->tlab_capacity(myThread()) / HeapWordSize));
size_t new_size = alloc / _target_refills;
//根据本地分配缓冲区大小允许的最大值/最小值来调整缓冲区的新大小
new_size = MIN2(MAX2(new_size, min_size()), max_size());
//内存对齐后的大小
size_t aligned_new_size = align_object_size(new_size);
if (PrintTLAB && Verbose) {
gclog_or_tty->print("TLAB new size: thread: " INTPTR_FORMAT " [id: %2d]"
" refills %d alloc: %8.6f desired_size: " SIZE_FORMAT " -> " SIZE_FORMAT "\n",
myThread(), myThread()->osthread()->thread_id(),
_target_refills, _allocation_fraction.average(), desired_size(), aligned_new_size);
}
set_desired_size(aligned_new_size);
set_refill_waste_limit(initial_refill_waste_limit());
}
}
void ThreadLocalAllocBuffer::accumulate_statistics() {
size_t capacity = Universe::heap()->tlab_capacity(myThread()) / HeapWordSize;
size_t unused = Universe::heap()->unsafe_max_tlab_alloc(myThread()) / HeapWordSize;
size_t used = capacity - unused;
// Update allocation history if a reasonable amount of eden was allocated.
bool update_allocation_history = used > 0.5 * capacity;
_gc_waste += (unsigned)remaining();
if (PrintTLAB && (_number_of_refills > 0 || Verbose)) {
print_stats("gc");
}
if (_number_of_refills > 0) {
if (update_allocation_history) {
// Average the fraction of eden allocated in a tlab by this
// thread for use in the next resize operation.
// _gc_waste is not subtracted because it's included in
// "used".
size_t allocation = _number_of_refills * desired_size();
double alloc_frac = allocation / (double) used;
_allocation_fraction.sample(alloc_frac);
}
global_stats()->update_allocating_threads();
global_stats()->update_number_of_refills(_number_of_refills);
global_stats()->update_allocation(_number_of_refills * desired_size());
global_stats()->update_gc_waste(_gc_waste);
global_stats()->update_slow_refill_waste(_slow_refill_waste);
global_stats()->update_fast_refill_waste(_fast_refill_waste);
} else {
assert(_number_of_refills == 0 && _fast_refill_waste == 0 &&
_slow_refill_waste == 0 && _gc_waste == 0,
"tlab stats == 0");
}
global_stats()->update_slow_allocations(_slow_allocations);
}
void ThreadLocalAllocBuffer::accumulate_statistics() {
Thread* thread = myThread();
size_t capacity = Universe::heap()->tlab_capacity(thread);
size_t used = Universe::heap()->tlab_used(thread);
_gc_waste += (unsigned)remaining();
size_t total_allocated = thread->allocated_bytes();
size_t allocated_since_last_gc = total_allocated - _allocated_before_last_gc;
_allocated_before_last_gc = total_allocated;
if (PrintTLAB && (_number_of_refills > 0 || Verbose)) {
print_stats("gc");
}
if (_number_of_refills > 0) {
// Update allocation history if a reasonable amount of eden was allocated.
bool update_allocation_history = used > 0.5 * capacity;
if (update_allocation_history) {
// Average the fraction of eden allocated in a tlab by this
// thread for use in the next resize operation.
// _gc_waste is not subtracted because it's included in
// "used".
// The result can be larger than 1.0 due to direct to old allocations.
// These allocations should ideally not be counted but since it is not possible
// to filter them out here we just cap the fraction to be at most 1.0.
double alloc_frac = MIN2(1.0, (double) allocated_since_last_gc / used);
_allocation_fraction.sample(alloc_frac);
}
global_stats()->update_allocating_threads();
global_stats()->update_number_of_refills(_number_of_refills);
global_stats()->update_allocation(_number_of_refills * desired_size());
global_stats()->update_gc_waste(_gc_waste);
global_stats()->update_slow_refill_waste(_slow_refill_waste);
global_stats()->update_fast_refill_waste(_fast_refill_waste);
} else {
assert(_number_of_refills == 0 && _fast_refill_waste == 0 &&
_slow_refill_waste == 0 && _gc_waste == 0,
"tlab stats == 0");
}
global_stats()->update_slow_allocations(_slow_allocations);
}
void ThreadLocalAllocBuffer::resize() {
// Compute the next tlab size using expected allocation amount
assert(ResizeTLAB, "Should not call this otherwise");
size_t alloc = (size_t)(_allocation_fraction.average() *
(Universe::heap()->tlab_capacity(myThread()) / HeapWordSize));
size_t new_size = alloc / _target_refills;
new_size = MIN2(MAX2(new_size, min_size()), max_size());
size_t aligned_new_size = align_object_size(new_size);
if (PrintTLAB && Verbose) {
gclog_or_tty->print("TLAB new size: thread: " INTPTR_FORMAT " [id: %2d]"
" refills %d alloc: %8.6f desired_size: " SIZE_FORMAT " -> " SIZE_FORMAT "\n",
p2i(myThread()), myThread()->osthread()->thread_id(),
_target_refills, _allocation_fraction.average(), desired_size(), aligned_new_size);
}
set_desired_size(aligned_new_size);
set_refill_waste_limit(initial_refill_waste_limit());
}
void ThreadLocalAllocBuffer::initialize() {
initialize(NULL, // start
NULL, // top
NULL); // end
set_desired_size(initial_desired_size());
// Following check is needed because at startup the main (primordial)
// thread is initialized before the heap is. The initialization for
// this thread is redone in startup_initialization below.
if (Universe::heap() != NULL) {
size_t capacity = Universe::heap()->tlab_capacity(myThread()) / HeapWordSize;
double alloc_frac = desired_size() * target_refills() / (double) capacity;
_allocation_fraction.sample(alloc_frac);
}
set_refill_waste_limit(initial_refill_waste_limit());
initialize_statistics();
}
size_t initial_refill_waste_limit() { return desired_size() / TLABRefillWasteFraction; }