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LibC: Unmap unused pages in aligned mallocs

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Bananymous
2026-07-16 10:22:56 +03:00
parent 8368dec30b
commit 33f941f2fd
1 changed files with 19 additions and 10 deletions
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29
userspace/libraries/LibC/malloc.cpp
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@@ -398,25 +398,34 @@ void* aligned_alloc(size_t alignment, size_t size)
static_assert(sizeof(MmapAllocationHeader) <= alignof(max_align_t)); static_assert(sizeof(MmapAllocationHeader) <= alignof(max_align_t));
const size_t mmap_size = alignment + size; size_t mmap_size = alignment + size;
void* address = mmap(nullptr, mmap_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); void* addr_ptr = mmap(nullptr, mmap_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (address == MAP_FAILED) if (addr_ptr == MAP_FAILED)
return nullptr; return nullptr;
uintptr_t addr = reinterpret_cast<uintptr_t>(addr_ptr);
uintptr_t data = addr + sizeof(MmapAllocationHeader);
if (const auto rem = data % alignment)
data += alignment - rem;
const size_t page_size = getpagesize();
if ((data - sizeof(MmapAllocationHeader)) - addr >= page_size)
{
const size_t pages_to_free = ((data - sizeof(MmapAllocationHeader)) - addr) / page_size;
munmap(addr_ptr, pages_to_free * page_size);
mmap_size -= pages_to_free * page_size;
addr += pages_to_free * page_size;
}
s_mmap_count++; s_mmap_count++;
s_mmap_bytes += mmap_size; s_mmap_bytes += mmap_size;
uintptr_t data = reinterpret_cast<uintptr_t>(address) + sizeof(MmapAllocationHeader);
if (auto rem = data % alignment)
data += alignment - rem;
// TODO: unmap possible unused pages in alignment, they are only allocated when accessed so doesn't really matter :^)
auto& header = reinterpret_cast<MmapAllocationHeader*>(data)[-1]; auto& header = reinterpret_cast<MmapAllocationHeader*>(data)[-1];
header = { header = {
.mmap_size = mmap_size, .mmap_size = mmap_size,
.offset = data - reinterpret_cast<uintptr_t>(address), .offset = data - addr,
}; };
return &header + 1; return &header + 1;
} }