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https://github.com/LadybirdBrowser/ladybird.git
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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.
84 lines
2.5 KiB
C++
84 lines
2.5 KiB
C++
/*
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* Copyright (c) 2021-2023, Andreas Kling <kling@serenityos.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/Platform.h>
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#include <AK/Random.h>
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#include <AK/Vector.h>
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#include <LibJS/Heap/BlockAllocator.h>
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#include <LibJS/Heap/HeapBlock.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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# include <sanitizer/lsan_interface.h>
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#endif
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#if defined(AK_OS_GNU_HURD) || (!defined(MADV_FREE) && !defined(MADV_DONTNEED))
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# define USE_FALLBACK_BLOCK_DEALLOCATION
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#endif
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namespace JS {
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BlockAllocator::~BlockAllocator()
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{
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for (auto* block : m_blocks) {
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ASAN_UNPOISON_MEMORY_REGION(block, HeapBlock::block_size);
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if (munmap(block, HeapBlock::block_size) < 0) {
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perror("munmap");
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VERIFY_NOT_REACHED();
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}
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}
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}
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void* BlockAllocator::allocate_block([[maybe_unused]] char const* name)
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{
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if (!m_blocks.is_empty()) {
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// To reduce predictability, take a random block from the cache.
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size_t random_index = get_random_uniform(m_blocks.size());
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auto* block = m_blocks.unstable_take(random_index);
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ASAN_UNPOISON_MEMORY_REGION(block, HeapBlock::block_size);
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LSAN_REGISTER_ROOT_REGION(block, HeapBlock::block_size);
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return block;
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}
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auto* block = (HeapBlock*)mmap(nullptr, HeapBlock::block_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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VERIFY(block != MAP_FAILED);
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LSAN_REGISTER_ROOT_REGION(block, HeapBlock::block_size);
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return block;
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}
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void BlockAllocator::deallocate_block(void* block)
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{
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VERIFY(block);
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#if defined(USE_FALLBACK_BLOCK_DEALLOCATION)
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// If we can't use any of the nicer techniques, unmap and remap the block to return the physical pages while keeping the VM.
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if (munmap(block, HeapBlock::block_size) < 0) {
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perror("munmap");
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VERIFY_NOT_REACHED();
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}
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if (mmap(block, HeapBlock::block_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0) != block) {
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perror("mmap");
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VERIFY_NOT_REACHED();
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}
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#elif defined(MADV_FREE)
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if (madvise(block, HeapBlock::block_size, MADV_FREE) < 0) {
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perror("madvise(MADV_FREE)");
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VERIFY_NOT_REACHED();
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}
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#elif defined(MADV_DONTNEED)
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if (madvise(block, HeapBlock::block_size, MADV_DONTNEED) < 0) {
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perror("madvise(MADV_DONTNEED)");
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VERIFY_NOT_REACHED();
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}
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#endif
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ASAN_POISON_MEMORY_REGION(block, HeapBlock::block_size);
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LSAN_UNREGISTER_ROOT_REGION(block, HeapBlock::block_size);
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m_blocks.append(block);
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}
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}
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