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ZGC: Convert zObjectAllocator to use Atomic<T>

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This commit is contained in:
Axel Boldt-Christmas 2026-01-05 13:54:17 +00:00
parent 40d1b642a4
commit f0737ceb89
2 changed files with 31 additions and 27 deletions
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39
src/hotspot/share/gc/z/zObjectAllocator.cpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -31,7 +31,7 @@
#include "gc/z/zPageAge.inline.hpp"
#include "gc/z/zPageType.hpp"
#include "gc/z/zValue.inline.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/atomic.hpp"
#include "runtime/safepoint.hpp"
#include "runtime/thread.hpp"
#include "utilities/align.hpp"
@ -40,16 +40,16 @@
ZObjectAllocator::PerAge::PerAge(ZPageAge age)
: _age(age),
_use_per_cpu_shared_small_pages(ZHeuristics::use_per_cpu_shared_small_pages()),
_shared_small_page(nullptr),
_shared_medium_page(nullptr),
_shared_small_page(),
_shared_medium_page(),
_medium_page_alloc_lock() {}
ZPage** ZObjectAllocator::PerAge::shared_small_page_addr() {
return _use_per_cpu_shared_small_pages ? _shared_small_page.addr() : _shared_small_page.addr(0);
Atomic<ZPage*>& ZObjectAllocator::PerAge::shared_small_page() {
return _use_per_cpu_shared_small_pages ? _shared_small_page.get() : _shared_small_page.get(0);
}
ZPage* const* ZObjectAllocator::PerAge::shared_small_page_addr() const {
return _use_per_cpu_shared_small_pages ? _shared_small_page.addr() : _shared_small_page.addr(0);
const Atomic<ZPage*>& ZObjectAllocator::PerAge::shared_small_page() const {
return _use_per_cpu_shared_small_pages ? _shared_small_page.get() : _shared_small_page.get(0);
}
ZPage* ZObjectAllocator::PerAge::alloc_page(ZPageType type, size_t size, ZAllocationFlags flags) {
@ -60,13 +60,13 @@ void ZObjectAllocator::PerAge::undo_alloc_page(ZPage* page) {
ZHeap::heap()->undo_alloc_page(page);
}
zaddress ZObjectAllocator::PerAge::alloc_object_in_shared_page(ZPage** shared_page,
zaddress ZObjectAllocator::PerAge::alloc_object_in_shared_page(Atomic<ZPage*>& shared_page,
ZPageType page_type,
size_t page_size,
size_t size,
ZAllocationFlags flags) {
zaddress addr = zaddress::null;
ZPage* page = AtomicAccess::load_acquire(shared_page);
ZPage* page = shared_page.load_acquire();
if (page != nullptr) {
addr = page->alloc_object_atomic(size);
@ -81,7 +81,7 @@ zaddress ZObjectAllocator::PerAge::alloc_object_in_shared_page(ZPage** shared_pa
retry:
// Install new page
ZPage* const prev_page = AtomicAccess::cmpxchg(shared_page, page, new_page);
ZPage* const prev_page = shared_page.compare_exchange(page, new_page);
if (prev_page != page) {
if (prev_page == nullptr) {
// Previous page was retired, retry installing the new page
@ -112,8 +112,8 @@ zaddress ZObjectAllocator::PerAge::alloc_object_in_shared_page(ZPage** shared_pa
zaddress ZObjectAllocator::PerAge::alloc_object_in_medium_page(size_t size,
ZAllocationFlags flags) {
zaddress addr = zaddress::null;
ZPage** shared_medium_page = _shared_medium_page.addr();
ZPage* page = AtomicAccess::load_acquire(shared_medium_page);
Atomic<ZPage*>& shared_medium_page = _shared_medium_page.get();
ZPage* page = shared_medium_page.load_acquire();
if (page != nullptr) {
addr = page->alloc_object_atomic(size);
@ -177,7 +177,7 @@ zaddress ZObjectAllocator::PerAge::alloc_medium_object(size_t size, ZAllocationF
}
zaddress ZObjectAllocator::PerAge::alloc_small_object(size_t size, ZAllocationFlags flags) {
return alloc_object_in_shared_page(shared_small_page_addr(), ZPageType::small, ZPageSizeSmall, size, flags);
return alloc_object_in_shared_page(shared_small_page(), ZPageType::small, ZPageSizeSmall, size, flags);
}
zaddress ZObjectAllocator::PerAge::alloc_object(size_t size, ZAllocationFlags flags) {
@ -197,8 +197,11 @@ void ZObjectAllocator::PerAge::retire_pages() {
assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
// Reset allocation pages
_shared_medium_page.set(nullptr);
_shared_small_page.set_all(nullptr);
_shared_medium_page.get().store_relaxed(nullptr);
ZValueIterator iter(&_shared_small_page);
for (Atomic<ZPage*>* shared_small_page; iter.next(&shared_small_page);) {
shared_small_page->store_relaxed(nullptr);
}
}
ZObjectAllocator::ZObjectAllocator()
@ -226,8 +229,8 @@ void ZObjectAllocator::retire_pages(ZPageAgeRange range) {
size_t ZObjectAllocator::fast_available(ZPageAge age) const {
assert(Thread::current()->is_Java_thread(), "Should be a Java thread");
ZPage* const* const shared_addr = allocator(age)->shared_small_page_addr();
const ZPage* const page = AtomicAccess::load_acquire(shared_addr);
const Atomic<ZPage*>& shared_addr = allocator(age)->shared_small_page();
const ZPage* const page = shared_addr.load_acquire();
if (page != nullptr) {
return page->remaining();
}

19
src/hotspot/share/gc/z/zObjectAllocator.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -31,29 +31,30 @@
#include "gc/z/zPage.hpp"
#include "gc/z/zPageAge.hpp"
#include "gc/z/zValue.hpp"
#include "runtime/atomic.hpp"
class ZObjectAllocator {
private:
class PerAge {
private:
const ZPageAge _age;
const bool _use_per_cpu_shared_small_pages;
ZPerCPU<ZPage*> _shared_small_page;
ZContended<ZPage*> _shared_medium_page;
ZLock _medium_page_alloc_lock;
const ZPageAge _age;
const bool _use_per_cpu_shared_small_pages;
ZPerCPU<Atomic<ZPage*>> _shared_small_page;
ZContended<Atomic<ZPage*>> _shared_medium_page;
ZLock _medium_page_alloc_lock;
public:
PerAge(ZPageAge age);
ZPage** shared_small_page_addr();
ZPage* const* shared_small_page_addr() const;
Atomic<ZPage*>& shared_small_page();
const Atomic<ZPage*>& shared_small_page() const;
ZPage* alloc_page(ZPageType type, size_t size, ZAllocationFlags flags);
void undo_alloc_page(ZPage* page);
// Allocate an object in a shared page. Allocate and
// atomically install a new page if necessary.
zaddress alloc_object_in_shared_page(ZPage** shared_page,
zaddress alloc_object_in_shared_page(Atomic<ZPage*>& shared_page,
ZPageType page_type,
size_t page_size,
size_t size,