GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/malloc_arena.cc
Date: 2025-04-20 02:34:28
Exec Total Coverage
Lines: 123 123 100.0%
Branches: 39 54 72.2%
Line Branch Exec Source
1 /**
2 * This file is part of the CernVM File System.
3 */
4
5 #define __STDC_FORMAT_MACROS
6
7
8 #include "malloc_arena.h"
9
10 #include <cassert>
11 #include <cstddef>
12 #include <cstring>
13 #include <new>
14
15 #include "util/smalloc.h"
16
17 using namespace std; // NOLINT
18
19
20 /**
21 * Walks through the free list starting at rover_ and looks for the first block
22 * larger than block_size. Returns NULL if no such block exists.
23 */
24 6997471 MallocArena::AvailBlockCtl *MallocArena::FindAvailBlock(
25 const int32_t block_size)
26 {
27 6997471 bool wrapped = false;
28 // Generally: p = LINK(q)
29 6997471 AvailBlockCtl *q = rover_;
30 AvailBlockCtl *p;
31 do {
32 2402953212 p = q->GetNextPtr(arena_);
33
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 2402953212 if (p->size >= block_size) {
34 5281679 rover_ = p->GetNextPtr(arena_);
35 5281679 return p;
36 }
37
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 2397671533 if (p == head_avail_) {
38
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 3705807 if (wrapped)
39 1715792 return NULL;
40 1990015 wrapped = true;
41 }
42 2395955741 q = p;
43 } while (true);
44 }
45
46
47 /**
48 * Creates a free block at the place of the reserved block ptr points into.
49 * The free block might need to be merged with adjacent lower and/or upper
50 * blocks. In these cases, the corresponding blocks are removed from the list
51 * of available blocks. Every allocated block has a predecessor and a
52 * successor in the arena. The newly created free block is added to the end of
53 * the list of available blocks.
54 */
55 5227259 void MallocArena::Free(void *ptr) {
56
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 5227259 assert(Contains(ptr));
57
58 5227259 no_reserved_--;
59
60 5227259 ReservedBlockCtl *block_ctl = reinterpret_cast<ReservedBlockCtl *>(
61 reinterpret_cast<char *>(ptr) - sizeof(ReservedBlockCtl));
62 5227259 char prior_tag = *(reinterpret_cast<char *>(block_ctl) - 1);
63
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 5227259 assert((prior_tag == kTagAvail) || (prior_tag == kTagReserved));
64
65 5227259 int32_t new_size = block_ctl->size();
66
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 5227259 assert(new_size > 0);
67 5227259 AvailBlockCtl *new_avail = reinterpret_cast<AvailBlockCtl *>(block_ctl);
68
69
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 5227259 if (prior_tag == kTagAvail) {
70 // Merge with block before and remove the block from the list
71 1932411 int32_t prior_size = reinterpret_cast<AvailBlockTag *>(
72 reinterpret_cast<char *>(block_ctl) - sizeof(AvailBlockTag))->size;
73
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 1932411 assert(prior_size > 0);
74 1932411 new_size += prior_size;
75 1932411 new_avail = reinterpret_cast<AvailBlockCtl *>(
76 1932411 reinterpret_cast<char *>(block_ctl) - prior_size);
77 // new_avail points now to the prior block
78 1932411 UnlinkAvailBlock(new_avail);
79
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 1932411 if (rover_ == new_avail)
80 22248 rover_ = head_avail_;
81 }
82
83 5227259 int32_t succ_size = *reinterpret_cast<int32_t *>(
84 5227259 reinterpret_cast<char *>(new_avail) + new_size);
85
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 5227259 if (succ_size >= 0) {
86 // Merge with succeeding block and remove the block from the list
87 2851059 AvailBlockCtl *succ_avail = reinterpret_cast<AvailBlockCtl *>(
88 2851059 reinterpret_cast<char *>(new_avail) + new_size);
89 2851059 UnlinkAvailBlock(succ_avail);
90 2851059 new_size += succ_size;
91
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 2851059 if (rover_ == succ_avail)
92 35763 rover_ = head_avail_;
93 }
94
95 // Set new free block's boundaries
96 5227259 new_avail->size = new_size;
97 5227259 new (AvailBlockTag::GetTagLocation(new_avail)) AvailBlockTag(new_size);
98
99 5227259 EnqueueAvailBlock(new_avail);
100 5227259 }
101
102
103 /**
104 * Inserts an available block at the end of the free list.
105 */
106 5227259 void MallocArena::EnqueueAvailBlock(AvailBlockCtl *block) {
107 5227259 AvailBlockCtl *next = head_avail_;
108 5227259 AvailBlockCtl *prev = head_avail_->GetPrevPtr(arena_);
109 5227259 next->link_prev = block->ConvertToLink(arena_);
110 5227259 prev->link_next = block->ConvertToLink(arena_);
111 5227259 block->link_next = head_avail_->ConvertToLink(arena_);
112 5227259 block->link_prev = prev->ConvertToLink(arena_);
113 5227259 }
114
115
116 /**
117 * The ptr points to the result of Malloc(). The size of the area is stored
118 * a few bytes before ptr.
119 */
120 8860705 uint32_t MallocArena::GetSize(void *ptr) const {
121
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 8860705 assert(Contains(ptr));
122
123 8860705 ReservedBlockCtl *block_ctl = reinterpret_cast<ReservedBlockCtl *>(
124 reinterpret_cast<char *>(ptr) - sizeof(ReservedBlockCtl));
125 8860705 int32_t size = block_ctl->size();
126
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 8860705 assert(size > 1);
127 8860705 return size - sizeof(ReservedBlockCtl) - 1;
128 }
129
130
131 /**
132 * Walks the list of available blocks starting from rover and allocates the
133 * first available spot that's large enough. Puts the reserved block at the end
134 * of the available one and, if necessary, removes the available one from the
135 * list of free blocks.
136 */
137 6997471 void *MallocArena::Malloc(const uint32_t size) {
138
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 6997471 assert(size > 0);
139
140 // Control word first, block type tag last
141 6997471 int32_t total_size = sizeof(ReservedBlockCtl) + size + 1;
142 6997471 total_size = RoundUp8(total_size);
143
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 6997471 if (total_size < kMinBlockSize)
144 29966 total_size = kMinBlockSize;
145
146 6997471 AvailBlockCtl *p = FindAvailBlock(total_size);
147
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 6997471 if (p == NULL)
148 1715792 return NULL;
149
150 5281679 no_reserved_++;
151 5281679 return ReserveBlock(p, total_size);
152 }
153
154
155 /**
156 * The arena starts with a pointer to this followed by the AvailBlockCtl of
157 * head_avail_, followed by a reserved tag to prevent it from being merged,
158 * followed by a free block spanning the arena until the end tag. The end tag
159 * is a single negative int, which mimics another reserved block.
160 */
161 171 MallocArena::MallocArena(unsigned arena_size)
162 171 : arena_(reinterpret_cast<char *>(sxmmap_align(arena_size)))
163 171 , head_avail_(reinterpret_cast<AvailBlockCtl *>(arena_ + sizeof(uint64_t)))
164 171 , rover_(head_avail_)
165 171 , no_reserved_(0)
166 171 , arena_size_(arena_size)
167 {
168
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 171 assert(arena_size_ > 0);
169
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 171 assert((arena_size_ % (2 * 1024 * 1024)) == 0); // Multiple of 2MB
170
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 171 assert(arena_size_ <= (512 * 1024 * 1024)); // <= 512MB
171
172 171 const unsigned char padding = 7;
173 // Size of the initial free block: everything minus arena boundaries
174 171 int32_t usable_size = arena_size_ -
175 (sizeof(uint64_t) + sizeof(AvailBlockCtl) + padding + 1 + sizeof(int32_t));
176
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 171 assert((usable_size % 8) == 0);
177
178 // First 8 bytes of arena: this pointer (occupies only 4 bytes on 32bit
179 // architectures, in which case the second 4 bytes are unused.)
180 171 *reinterpret_cast<MallocArena **>(arena_) = this;
181
182 // The initial large free block
183 AvailBlockCtl *free_block =
184 171 new (arena_ + sizeof(uint64_t) + sizeof(AvailBlockCtl) + padding + 1)
185 171 AvailBlockCtl();
186 171 free_block->size = usable_size;
187 171 free_block->link_next = free_block->link_prev =
188 171 head_avail_->ConvertToLink(arena_);
189 171 new (AvailBlockTag::GetTagLocation(free_block)) AvailBlockTag(usable_size);
190
191 171 head_avail_->size = 0;
192 342 head_avail_->link_next = head_avail_->link_prev =
193 171 free_block->ConvertToLink(arena_);
194
195 // Prevent succeeding blocks from merging
196 171 *(reinterpret_cast<char *>(free_block) - 1) = kTagReserved;
197 // Final tag: reserved block marker
198 171 *reinterpret_cast<int32_t *>(arena_ + arena_size_ - sizeof(int32_t)) = -1;
199 171 }
200
201
202 /**
203 * Initializes the arena with repeated copies of the given pattern. Used for
204 * testing.
205 */
206 1 MallocArena *MallocArena::CreateInitialized(
207 unsigned arena_size,
208 unsigned char pattern)
209 {
210 1 MallocArena *result = new MallocArena(arena_size);
211 // At this point, there is one big free block linked to by head_avail_
212 1 AvailBlockCtl *free_block = result->head_avail_->GetNextPtr(result->arena_);
213
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 1 assert(free_block != result->head_avail_);
214
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 1 assert(free_block->size > 0);
215 // Strip control information at both ends of the block
216 1 int usable_size = free_block->size -
217 (sizeof(AvailBlockCtl) + sizeof(AvailBlockTag));
218
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 1 assert(usable_size > 0);
219 1 memset(free_block + 1, pattern, usable_size);
220 1 return result;
221 }
222
223
224 168 MallocArena::~MallocArena() {
225 168 sxunmap(arena_, arena_size_);
226 168 }
227
228
229 /**
230 * Given the free block "block", cuts out a new reserved block of size
231 * block_size at the end of the free block. Returns a pointer usable by the
232 * application.
233 */
234 5281679 void *MallocArena::ReserveBlock(
235 AvailBlockCtl *block,
236 int32_t block_size)
237 {
238
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 5281679 assert(block->size >= block_size);
239
240 5281679 int32_t remaining_size = block->size - block_size;
241 // Avoid creation of very small blocks
242
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 5281679 if (remaining_size < kMinBlockSize) {
243 427091 block_size += remaining_size;
244 427091 remaining_size = 0;
245 }
246
247 // Update the list of available blocks
248
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 5281679 if (remaining_size == 0) {
249 // Remove free block p from the list of available blocks
250 427091 UnlinkAvailBlock(block);
251 } else {
252 4854588 block->ShrinkTo(remaining_size);
253 }
254
255 // Place the new allocation, which also sets the block type tag at the end
256 5281679 char *new_block = reinterpret_cast<char *>(block) + remaining_size;
257 5281679 new (new_block) ReservedBlockCtl(block_size);
258 5281679 return new_block + sizeof(ReservedBlockCtl);
259 }
260
261
262 /**
263 * Removes the given block from the doubly linked free block list. This happens
264 * when two adjacent free blocks are created in Free() and then merged. Or if
265 * a block gets fully used in Malloc().
266 */
267 5210561 void MallocArena::UnlinkAvailBlock(AvailBlockCtl *block) {
268 5210561 AvailBlockCtl *next = block->GetNextPtr(arena_);
269 5210561 AvailBlockCtl *prev = block->GetPrevPtr(arena_);
270 5210561 prev->link_next = block->link_next;
271 5210561 next->link_prev = block->link_prev;
272 5210561 }
273