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a6bf253602
Before this change, we were hard-coding 4 KiB. This meant that systems with a 16 KiB native page size were wasting 12 KiB per HeapBlock on nothing, leading to worse locality and more mmap/madvise churn. We now query the system page size on startup and use that as the HeapBlock size. The only downside here is that some of the pointer math for finding the base of a HeapBlock now has to use a runtime computed value instead of a compile time constant. But that's a small price to pay for what we get.
64 lines
2.3 KiB
C++
64 lines
2.3 KiB
C++
/*
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* Copyright (c) 2020-2024, Andreas Kling <andreas@ladybird.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Assertions.h>
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#include <AK/NonnullOwnPtr.h>
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#include <AK/Platform.h>
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#include <LibJS/Heap/Heap.h>
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#include <LibJS/Heap/HeapBlock.h>
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#include <stdio.h>
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#include <sys/mman.h>
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#ifdef HAS_ADDRESS_SANITIZER
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# include <sanitizer/asan_interface.h>
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#endif
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namespace JS {
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size_t HeapBlockBase::block_size = PAGE_SIZE;
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NonnullOwnPtr<HeapBlock> HeapBlock::create_with_cell_size(Heap& heap, CellAllocator& cell_allocator, size_t cell_size, [[maybe_unused]] char const* class_name)
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{
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char const* name = nullptr;
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auto* block = static_cast<HeapBlock*>(cell_allocator.block_allocator().allocate_block(name));
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new (block) HeapBlock(heap, cell_allocator, cell_size);
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return NonnullOwnPtr<HeapBlock>(NonnullOwnPtr<HeapBlock>::Adopt, *block);
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}
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HeapBlock::HeapBlock(Heap& heap, CellAllocator& cell_allocator, size_t cell_size)
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: HeapBlockBase(heap)
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, m_cell_allocator(cell_allocator)
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, m_cell_size(cell_size)
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{
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VERIFY(cell_size >= sizeof(FreelistEntry));
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ASAN_POISON_MEMORY_REGION(m_storage, block_size - sizeof(HeapBlock));
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}
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void HeapBlock::deallocate(Cell* cell)
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{
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VERIFY(is_valid_cell_pointer(cell));
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VERIFY(!m_freelist || is_valid_cell_pointer(m_freelist));
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VERIFY(cell->state() == Cell::State::Live);
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VERIFY(!cell->is_marked());
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cell->~Cell();
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auto* freelist_entry = new (cell) FreelistEntry();
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freelist_entry->set_state(Cell::State::Dead);
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freelist_entry->next = m_freelist;
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m_freelist = freelist_entry;
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#ifdef HAS_ADDRESS_SANITIZER
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auto dword_after_freelist = round_up_to_power_of_two(reinterpret_cast<uintptr_t>(freelist_entry) + sizeof(FreelistEntry), 8);
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VERIFY((dword_after_freelist - reinterpret_cast<uintptr_t>(freelist_entry)) <= m_cell_size);
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VERIFY(m_cell_size >= sizeof(FreelistEntry));
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// We can't poision the cell tracking data, nor the FreeListEntry's vtable or next pointer
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// This means there's sizeof(FreelistEntry) data at the front of each cell that is always read/write
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// On x86_64, this ends up being 24 bytes due to the size of the FreeListEntry's vtable, while on x86, it's only 12 bytes.
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ASAN_POISON_MEMORY_REGION(reinterpret_cast<void*>(dword_after_freelist), m_cell_size - sizeof(FreelistEntry));
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#endif
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}
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}
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