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/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Format.h>
#include <Kernel/Memory/MemoryManager.h>
#include <Kernel/Memory/PhysicalPage.h>
#include <Kernel/Memory/PhysicalZone.h>
namespace Kernel::Memory {
PhysicalPageEntry& PhysicalZone::get_freelist_entry(ChunkIndex index) const
{
return MM.get_physical_page_entry(m_base_address.offset(index * ZONE_CHUNK_SIZE));
}
PhysicalZone::PhysicalZone(PhysicalAddress base_address, size_t page_count)
: m_base_address(base_address)
, m_page_count(page_count)
, m_used_chunks(0)
{
size_t const chunk_count = page_count * 2;
for (int order = max_order; order >= 0; --order) {
auto& bucket = m_buckets[order];
size_t block_size = 2u << order;
size_t bitmap_size_for_order = ceil_div((size_t)(chunk_count / block_size), (size_t)2);
bucket.order = order;
if (bitmap_size_for_order)
bucket.bitmap.grow(bitmap_size_for_order, false);
}
auto first_order = __builtin_ctz(page_count);
size_t block_size = 2u << first_order;
auto& bucket = m_buckets[first_order];
size_t remaining_chunk_count = chunk_count;
size_t initial_bundle_count = remaining_chunk_count / block_size;
size_t offset = 0;
for (size_t i = 0; i < initial_bundle_count; ++i) {
ChunkIndex index = offset + i;
bucket.set_buddy_bit(index, true);
auto& freelist_entry = get_freelist_entry(index).freelist;
freelist_entry.next_index = bucket.freelist;
freelist_entry.prev_index = -1;
bucket.freelist = index;
remaining_chunk_count -= block_size;
offset += block_size;
}
}
Optional<PhysicalAddress> PhysicalZone::allocate_block(size_t order)
{
size_t block_size = 2u << order;
auto result = allocate_block_impl(order);
if (!result.has_value())
return {};
m_used_chunks += block_size;
VERIFY(!(result.value() & 1));
return m_base_address.offset(result.value() * ZONE_CHUNK_SIZE);
}
Optional<PhysicalZone::ChunkIndex> PhysicalZone::allocate_block_impl(size_t order)
{
if (order > max_order)
return {};
size_t block_size = 2u << order;
auto& bucket = m_buckets[order];
if (bucket.freelist == -1) {
// The freelist for this order is empty, try to allocate a block from one order higher, and split it.
auto buddies = allocate_block_impl(order + 1);
if (!buddies.has_value()) {
// Looks like we're unable to satisfy this allocation request.
return {};
}
// Split the block from order+1 into two parts.
// We keep one (in the freelist for this order) and return the other.
ChunkIndex index = buddies.value();
// First half goes in the freelist
auto& freelist_entry = get_freelist_entry(index).freelist;
freelist_entry.next_index = -1;
freelist_entry.prev_index = -1;
bucket.freelist = index;
VERIFY(bucket.get_buddy_bit(index) == false);
// Set buddy bit to 1 (one used, one unused).
bucket.set_buddy_bit(index, true);
// Second half is returned.
return index + block_size;
}
// Freelist has at least one entry, return that.
ChunkIndex index = bucket.freelist;
bucket.freelist = get_freelist_entry(bucket.freelist).freelist.next_index;
if (bucket.freelist != -1) {
get_freelist_entry(bucket.freelist).freelist.prev_index = -1;
}
VERIFY(bucket.get_buddy_bit(index) == true);
bucket.set_buddy_bit(index, false);
return index;
}
void PhysicalZone::deallocate_block(PhysicalAddress address, size_t order)
{
size_t block_size = 2u << order;
ChunkIndex index = (address.get() - m_base_address.get()) / ZONE_CHUNK_SIZE;
deallocate_block_impl(index, order);
m_used_chunks -= block_size;
}
void PhysicalZone::deallocate_block_impl(ChunkIndex index, size_t order)
{
size_t block_size = 2u << order;
// Basic algorithm:
// If the buddy block is free (buddy bit is 1 -- because this block was the only used one):
// Then,
// 1. Merge with buddy.
// 2. Return the merged block to order+1.
// Else (buddy bit is 0 -- because both blocks are used)
// 1. Add the block to the freelist.
// 2. Set buddy bit to 1.
auto& bucket = m_buckets[order];
if (bucket.get_buddy_bit(index)) {
// Buddy is free! Merge with buddy and coalesce upwards to the next order.
auto buddy_bit_index = bucket.buddy_bit_index(index);
ChunkIndex buddy_base_index = (buddy_bit_index << 1) << (1 + order);
if (index == buddy_base_index)
remove_from_freelist(bucket, buddy_base_index + block_size);
else
remove_from_freelist(bucket, buddy_base_index);
bucket.set_buddy_bit(index, false);
deallocate_block_impl(buddy_base_index, order + 1);
} else {
// Buddy is in use. Add freed block to freelist and set buddy bit to 1.
if (bucket.freelist != -1) {
get_freelist_entry(bucket.freelist).freelist.prev_index = index;
}
auto& freelist_entry = get_freelist_entry(index).freelist;
freelist_entry.next_index = bucket.freelist;
freelist_entry.prev_index = -1;
bucket.freelist = index;
bucket.set_buddy_bit(index, true);
}
}
void PhysicalZone::remove_from_freelist(BuddyBucket& bucket, ChunkIndex index)
{
auto& freelist_entry = get_freelist_entry(index).freelist;
VERIFY(freelist_entry.prev_index >= -1);
VERIFY(freelist_entry.next_index >= -1);
if (freelist_entry.prev_index != -1) {
auto& prev_entry = get_freelist_entry(freelist_entry.prev_index).freelist;
prev_entry.next_index = freelist_entry.next_index;
}
if (freelist_entry.next_index != -1) {
auto& next_entry = get_freelist_entry(freelist_entry.next_index).freelist;
next_entry.prev_index = freelist_entry.prev_index;
}
if (bucket.freelist == index)
bucket.freelist = freelist_entry.next_index;
freelist_entry.next_index = -1;
freelist_entry.prev_index = -1;
}
void PhysicalZone::dump() const
{
dbgln("(( {} used, {} available, page_count: {} ))", m_used_chunks, available(), m_page_count);
for (size_t i = 0; i <= max_order; ++i) {
auto& bucket = m_buckets[i];
dbgln("[{:2} / {:4}] ", i, (size_t)(2u << i));
auto entry = bucket.freelist;
while (entry != -1) {
dbgln(" {}", entry);
entry = get_freelist_entry(entry).freelist.next_index;
}
}
}
}
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