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Apply PLAB card-alignment removal to ShenandoahSerialAllocator

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This commit is contained in:
Xiaolong Peng 2026-05-29 17:16:52 -07:00
parent 6804dcec27
commit 9507032651
1 changed files with 12 additions and 34 deletions
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46
src/hotspot/share/gc/shenandoah/shenandoahSerialAllocator.cpp
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@ -22,7 +22,6 @@
*
*/
#include "gc/shared/cardTable.hpp"
#include "gc/shared/plab.hpp"
#include "gc/shenandoah/shenandoahAllocRequest.hpp"
#include "gc/shenandoah/shenandoahFreeSet.hpp"
@ -273,7 +272,7 @@ HeapWord* ShenandoahSerialAllocator::try_allocate_from_mutator(ShenandoahAllocRe
// Allocate within region r for the given request. This handles:
// 1. Region recycling and affiliation setup for new (empty) regions
// 2. LAB sizing (TLAB/GCLAB shrink-to-fit, PLAB card-alignment)
// 2. LAB sizing (TLAB/GCLAB/PLAB shrink-to-fit)
// 3. Partition accounting (used, empty counts, retirement)
HeapWord* ShenandoahSerialAllocator::try_allocate_in(ShenandoahHeapRegion* r, ShenandoahAllocRequest& req, bool& in_new_region) {
assert(_free_set->has_alloc_capacity(r), "Performance: should avoid full regions on this path: %zu", r->index());
@ -309,41 +308,20 @@ HeapWord* ShenandoahSerialAllocator::try_allocate_in(ShenandoahHeapRegion* r, Sh
}
}
// Perform the actual allocation: LABs may be shrunk to fit, PLABs must be card-aligned.
// Perform the actual allocation: LABs (TLAB/GCLAB/PLAB) may be shrunk to fit.
if (req.is_lab_alloc()) {
size_t adjusted_size = req.size();
size_t free = r->free();
if (req.is_old()) {
assert(heap->mode()->is_generational(), "PLABs are only for generational mode");
assert(_free_set->_partitions.in_free_set(ShenandoahFreeSetPartitionId::OldCollector, r->index()),
"PLABS must be allocated in old_collector_free regions");
size_t usable_free = _free_set->get_usable_free_words(free);
if (adjusted_size > usable_free) {
adjusted_size = usable_free;
}
adjusted_size = align_down(adjusted_size, CardTable::card_size_in_words());
if (adjusted_size >= req.min_size()) {
result = _free_set->allocate_aligned_plab(adjusted_size, req, r);
assert(result != nullptr, "allocate must succeed");
req.set_actual_size(adjusted_size);
} else {
log_trace(gc, free)("Failed to shrink PLAB request (%zu) in region %zu to %zu"
" because min_size() is %zu", req.size(), r->index(), adjusted_size, req.min_size());
}
size_t free = align_down(r->free() >> LogHeapWordSize, MinObjAlignment);
if (adjusted_size > free) {
adjusted_size = free;
}
if (adjusted_size >= req.min_size()) {
result = r->allocate(adjusted_size, req);
assert(result != nullptr, "Allocation must succeed: free %zu, actual %zu", free, adjusted_size);
req.set_actual_size(adjusted_size);
} else {
free = align_down(free >> LogHeapWordSize, MinObjAlignment);
if (adjusted_size > free) {
adjusted_size = free;
}
if (adjusted_size >= req.min_size()) {
result = r->allocate(adjusted_size, req);
assert(result != nullptr, "Allocation must succeed: free %zu, actual %zu", free, adjusted_size);
req.set_actual_size(adjusted_size);
} else {
log_trace(gc, free)("Failed to shrink TLAB or GCLAB request (%zu) in region %zu to %zu"
" because min_size() is %zu", req.size(), r->index(), adjusted_size, req.min_size());
}
log_trace(gc, free)("Failed to shrink LAB request (%zu) in region %zu to %zu"
" because min_size() is %zu", req.size(), r->index(), adjusted_size, req.min_size());
}
} else {
size_t size = req.size();