void AdaptiveSizePolicy::check_gc_overhead_limit(
size_t young_live,
size_t eden_live,
size_t max_old_gen_size,
size_t max_eden_size,
bool is_full_gc,
GCCause::Cause gc_cause,
CollectorPolicy* collector_policy) {
// Ignore explicit GC's. Exiting here does not set the flag and
// does not reset the count. Updating of the averages for system
// GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
if (GCCause::is_user_requested_gc(gc_cause) ||
GCCause::is_serviceability_requested_gc(gc_cause)) {
return;
}
// eden_limit is the upper limit on the size of eden based on
// the maximum size of the young generation and the sizes
// of the survivor space.
// The question being asked is whether the gc costs are high
// and the space being recovered by a collection is low.
// free_in_young_gen is the free space in the young generation
// after a collection and promo_live is the free space in the old
// generation after a collection.
//
// Use the minimum of the current value of the live in the
// young gen or the average of the live in the young gen.
// If the current value drops quickly, that should be taken
// into account (i.e., don't trigger if the amount of free
// space has suddenly jumped up). If the current is much
// higher than the average, use the average since it represents
// the longer term behavor.
const size_t live_in_eden =
MIN2(eden_live, (size_t) avg_eden_live()->average());
const size_t free_in_eden = max_eden_size > live_in_eden ?
max_eden_size - live_in_eden : 0;
const size_t free_in_old_gen = (size_t)(max_old_gen_size - avg_old_live()->average());
const size_t total_free_limit = free_in_old_gen + free_in_eden;
const size_t total_mem = max_old_gen_size + max_eden_size;
const double mem_free_limit = total_mem * (GCHeapFreeLimit/100.0);
const double mem_free_old_limit = max_old_gen_size * (GCHeapFreeLimit/100.0);
const double mem_free_eden_limit = max_eden_size * (GCHeapFreeLimit/100.0);
const double gc_cost_limit = GCTimeLimit/100.0;
size_t promo_limit = (size_t)(max_old_gen_size - avg_old_live()->average());
// But don't force a promo size below the current promo size. Otherwise,
// the promo size will shrink for no good reason.
promo_limit = MAX2(promo_limit, _promo_size);
if (PrintAdaptiveSizePolicy && (Verbose ||
(free_in_old_gen < (size_t) mem_free_old_limit &&
free_in_eden < (size_t) mem_free_eden_limit))) {
gclog_or_tty->print_cr(
"PSAdaptiveSizePolicy::compute_generation_free_space limits:"
" promo_limit: " SIZE_FORMAT
" max_eden_size: " SIZE_FORMAT
" total_free_limit: " SIZE_FORMAT
" max_old_gen_size: " SIZE_FORMAT
" max_eden_size: " SIZE_FORMAT
" mem_free_limit: " SIZE_FORMAT,
promo_limit, max_eden_size, total_free_limit,
max_old_gen_size, max_eden_size,
(size_t) mem_free_limit);
}
bool print_gc_overhead_limit_would_be_exceeded = false;
if (is_full_gc) {
if (gc_cost() > gc_cost_limit &&
free_in_old_gen < (size_t) mem_free_old_limit &&
free_in_eden < (size_t) mem_free_eden_limit) {
// Collections, on average, are taking too much time, and
// gc_cost() > gc_cost_limit
// we have too little space available after a full gc.
// total_free_limit < mem_free_limit
// where
// total_free_limit is the free space available in
// both generations
// total_mem is the total space available for allocation
// in both generations (survivor spaces are not included
// just as they are not included in eden_limit).
// mem_free_limit is a fraction of total_mem judged to be an
// acceptable amount that is still unused.
// The heap can ask for the value of this variable when deciding
// whether to thrown an OutOfMemory error.
// Note that the gc time limit test only works for the collections
// of the young gen + tenured gen and not for collections of the
// permanent gen. That is because the calculation of the space
// freed by the collection is the free space in the young gen +
// tenured gen.
// At this point the GC overhead limit is being exceeded.
inc_gc_overhead_limit_count();
if (UseGCOverheadLimit) {
if (gc_overhead_limit_count() >=
AdaptiveSizePolicyGCTimeLimitThreshold){
// All conditions have been met for throwing an out-of-memory
set_gc_overhead_limit_exceeded(true);
// Avoid consecutive OOM due to the gc time limit by resetting
// the counter.
reset_gc_overhead_limit_count();
} else {
// The required consecutive collections which exceed the
// GC time limit may or may not have been reached. We
// are approaching that condition and so as not to
// throw an out-of-memory before all SoftRef's have been
// cleared, set _should_clear_all_soft_refs in CollectorPolicy.
// The clearing will be done on the next GC.
bool near_limit = gc_overhead_limit_near();
if (near_limit) {
collector_policy->set_should_clear_all_soft_refs(true);
if (PrintGCDetails && Verbose) {
gclog_or_tty->print_cr(" Nearing GC overhead limit, "
"will be clearing all SoftReference");
}
}
}
}
// Set this even when the overhead limit will not
// cause an out-of-memory. Diagnostic message indicating
// that the overhead limit is being exceeded is sometimes
// printed.
print_gc_overhead_limit_would_be_exceeded = true;
} else {
// Did not exceed overhead limits
reset_gc_overhead_limit_count();
}
}
if (UseGCOverheadLimit && PrintGCDetails && Verbose) {
if (gc_overhead_limit_exceeded()) {
gclog_or_tty->print_cr(" GC is exceeding overhead limit "
"of %d%%", GCTimeLimit);
reset_gc_overhead_limit_count();
} else if (print_gc_overhead_limit_would_be_exceeded) {
assert(gc_overhead_limit_count() > 0, "Should not be printing");
gclog_or_tty->print_cr(" GC would exceed overhead limit "
"of %d%% %d consecutive time(s)",
GCTimeLimit, gc_overhead_limit_count());
}
}
}
// Tests conditions indicate the GC overhead limit is being approached.
bool gc_overhead_limit_near() {
return gc_overhead_limit_count() >=
(AdaptiveSizePolicyGCTimeLimitThreshold - 1);
}