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#include <kernel/memory/block_list_allocator.hpp>
#include <kernel/memory/heap_allocator.hpp>
#include <kapi/memory.hpp>
#include <kapi/system.hpp>
#include <kstd/mutex>
#include <kstd/units>
#include <bit>
#include <cstddef>
#include <cstdint>
#include <memory>
using namespace kstd::units_literals;
namespace kernel::memory
{
namespace
{
[[nodiscard]] constexpr auto align_up(std::byte * pointer, kstd::units::bytes alignment) noexcept -> std::byte *
{
auto const remainder = std::bit_cast<std::uintptr_t>(pointer) % static_cast<std::size_t>(alignment);
return remainder == 0 ? pointer : pointer + static_cast<std::size_t>(alignment) - remainder;
}
} // namespace
block_list_allocator::block_list_allocator(kapi::memory::linear_address base) noexcept
: heap_allocator{}
, m_base{base}
, m_frontier{base}
, m_block_list{}
, m_lock{}
{}
auto block_list_allocator::allocate(kstd::units::bytes size, kstd::units::bytes alignment) noexcept -> void *
{
kstd::lock_guard guard{m_lock};
for (auto attempt = 0uz; attempt < 2uz; ++attempt)
{
auto current = m_block_list;
while (current != nullptr)
{
if (current->free)
{
auto const raw_block = reinterpret_cast<std::byte *>(current);
auto const unaligned_payload = raw_block + allocated_metadata_size;
auto const aligned_payload = align_up(unaligned_payload, alignment);
auto const required_padding = static_cast<kstd::units::bytes>(aligned_payload - unaligned_payload);
auto const total_required_size = required_padding + allocated_metadata_size + size;
if (current->usable_size >= total_required_size)
{
auto const payload_header = aligned_payload - sizeof(block_header *) - sizeof(block_header);
auto const front_padding = static_cast<kstd::units::bytes>(payload_header - raw_block);
auto payload_block = current;
if (front_padding >= allocated_metadata_size + minimum_allocation_size)
{
payload_block = reinterpret_cast<block_header *>(payload_header);
std::construct_at(payload_block, current->usable_size - front_padding, true, current->next);
if (payload_block->next)
{
payload_block->next->prev = payload_block;
}
current->usable_size = front_padding - allocated_metadata_size;
current->next = payload_block;
payload_block->prev = current;
}
auto const header_size =
static_cast<kstd::units::bytes>(aligned_payload - reinterpret_cast<std::byte *>(payload_block));
auto const payload_size = header_size - allocated_metadata_size + size;
split(payload_block, payload_size, 0_B);
payload_block->free = false;
auto back_pointer = reinterpret_cast<block_header **>(aligned_payload - sizeof(block_header *));
*back_pointer = payload_block;
return reinterpret_cast<void *>(aligned_payload);
}
}
current = current->next;
}
auto const search_size = size + alignment;
if (attempt == 0uz && !expand(search_size))
{
return nullptr;
}
}
return nullptr;
}
auto block_list_allocator::deallocate(void * ptr) noexcept -> void
{
if (!ptr)
{
return;
}
kstd::lock_guard guard{m_lock};
auto const aligned_payload = reinterpret_cast<std::byte *>(ptr);
auto back_pointer = reinterpret_cast<block_header **>(aligned_payload - sizeof(block_header *));
auto block = *back_pointer;
block->free = true;
coalesce(block);
}
auto block_list_allocator::expand(kstd::units::bytes size) noexcept -> bool
{
auto const total_required_size = size + allocated_metadata_size;
auto const frames_needed = (total_required_size + kapi::memory::frame::size - 1_B) / kapi::memory::frame::size;
auto const flags = kapi::memory::page_mapper::flags::writable | kapi::memory::page_mapper::flags::supervisor_only |
kapi::memory::page_mapper::flags::global;
for (auto i = 0uz; i < frames_needed; ++i)
{
auto frame = kapi::memory::allocate_frame();
if (!frame)
{
kapi::system::panic("[OS:Heap] OOM when expanding heap.");
return false;
}
auto page = kapi::memory::page::containing(m_frontier + i * kapi::memory::page::size);
kapi::memory::map(page, *frame, flags);
}
auto block = static_cast<block_header *>(m_frontier);
std::construct_at(block, frames_needed * kapi::memory::frame::size - allocated_metadata_size, true, nullptr,
nullptr);
m_frontier += frames_needed * kapi::memory::frame::size;
if (!m_block_list)
{
m_block_list = block;
}
else
{
auto current = m_block_list;
while (current->next)
{
current = current->next;
}
current->next = block;
block->prev = current;
}
coalesce(block);
return true;
}
auto block_list_allocator::coalesce(block_header * block) noexcept -> void
{
if (block->next && block->next->free)
{
auto follower = block->next;
block->usable_size += follower->usable_size + allocated_metadata_size;
block->next = follower->next;
if (block->next)
{
block->next->prev = block;
}
std::destroy_at(follower);
}
if (block->prev && block->prev->free)
{
auto leader = block->prev;
leader->usable_size += block->usable_size + allocated_metadata_size;
leader->next = block->next;
if (block->next)
{
block->next->prev = leader;
}
std::destroy_at(block);
}
}
auto block_list_allocator::split(block_header * block, kstd::units::bytes size, kstd::units::bytes padding) noexcept
-> void
{
auto const new_block_size = size + padding;
if (block->usable_size > new_block_size + allocated_metadata_size + minimum_allocation_size)
{
auto raw_block = reinterpret_cast<std::byte *>(block);
auto new_block = reinterpret_cast<block_header *>(raw_block + allocated_metadata_size + new_block_size);
std::construct_at(new_block, block->usable_size - new_block_size - allocated_metadata_size, true, block->next,
block);
if (new_block->next)
{
new_block->next->prev = new_block;
}
block->usable_size = new_block_size;
block->next = new_block;
}
}
} // namespace kernel::memory
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