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8366781: Parallel: Include OS free memory in GC selection heuristics

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Reviewed-by: gli, iwalulya
This commit is contained in:
Albert Mingkun Yang 2025-10-27 10:07:55 +00:00
parent e9479b517a
commit 91e1dcb108
1 changed files with 36 additions and 11 deletions
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47
src/hotspot/share/gc/parallel/psScavenge.cpp
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@ -521,31 +521,56 @@ void PSScavenge::clean_up_failed_promotion() {
}
bool PSScavenge::should_attempt_scavenge() {
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
const bool ShouldRunYoungGC = true;
const bool ShouldRunFullGC = false;
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
PSYoungGen* young_gen = heap->young_gen();
PSOldGen* old_gen = heap->old_gen();
if (!young_gen->to_space()->is_empty()) {
log_debug(gc, ergo)("To-space is not empty; should run full-gc instead.");
return false;
log_debug(gc, ergo)("To-space is not empty; run full-gc instead.");
return ShouldRunFullGC;
}
// Test to see if the scavenge will likely fail.
// Check if the predicted promoted bytes will overflow free space in old-gen.
PSAdaptiveSizePolicy* policy = heap->size_policy();
size_t avg_promoted = (size_t) policy->padded_average_promoted_in_bytes();
size_t promotion_estimate = MIN2(avg_promoted, young_gen->used_in_bytes());
// Total free size after possible old gen expansion
size_t free_in_old_gen = old_gen->max_gen_size() - old_gen->used_in_bytes();
bool result = promotion_estimate < free_in_old_gen;
size_t free_in_old_gen_with_expansion = old_gen->max_gen_size() - old_gen->used_in_bytes();
log_trace(gc, ergo)("%s scavenge: average_promoted %zu padded_average_promoted %zu free in old gen %zu",
result ? "Do" : "Skip", (size_t) policy->average_promoted_in_bytes(),
(size_t) policy->padded_average_promoted_in_bytes(),
free_in_old_gen);
log_trace(gc, ergo)("average_promoted %zu; padded_average_promoted %zu",
(size_t) policy->average_promoted_in_bytes(),
(size_t) policy->padded_average_promoted_in_bytes());
return result;
if (promotion_estimate >= free_in_old_gen_with_expansion) {
log_debug(gc, ergo)("Run full-gc; predicted promotion size >= max free space in old-gen: %zu >= %zu",
promotion_estimate, free_in_old_gen_with_expansion);
return ShouldRunFullGC;
}
if (UseAdaptiveSizePolicy) {
// Also checking OS has enough free memory to commit and expand old-gen.
// Otherwise, the recorded gc-pause-time might be inflated to include time
// of OS preparing free memory, resulting in inaccurate young-gen resizing.
assert(old_gen->committed().byte_size() >= old_gen->used_in_bytes(), "inv");
// Use uint64_t instead of size_t for 32bit compatibility.
uint64_t free_mem_in_os;
if (os::free_memory(free_mem_in_os)) {
size_t actual_free = (size_t)MIN2(old_gen->committed().byte_size() - old_gen->used_in_bytes() + free_mem_in_os,
(uint64_t)SIZE_MAX);
if (promotion_estimate > actual_free) {
log_debug(gc, ergo)("Run full-gc; predicted promotion size > free space in old-gen and OS: %zu > %zu",
promotion_estimate, actual_free);
return ShouldRunFullGC;
}
}
}
// No particular reasons to run full-gc, so young-gc.
return ShouldRunYoungGC;
}
// Adaptive size policy support.