1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/BuiltinWrappers.h>
#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 = count_trailing_zeroes(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 const& 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;
}
}
}
}
|
