1 /*
2 * Copyright (C) 2013 Google Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met:
7 *
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above
11 * copyright notice, this list of conditions and the following disclaimer
12 * in the documentation and/or other materials provided with the
13 * distribution.
14 * * Neither the name of Google Inc. nor the names of its
15 * contributors may be used to endorse or promote products derived from
16 * this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31 #include "config.h"
32 #include "wtf/PartitionAlloc.h"
33
34 #include <string.h>
35
36 #ifndef NDEBUG
37 #include <stdio.h>
38 #endif
39
40 // Two partition pages are used as guard / metadata page so make sure the super
41 // page size is bigger.
42 COMPILE_ASSERT(WTF::kPartitionPageSize * 4 <= WTF::kSuperPageSize, ok_super_page_size);
43 COMPILE_ASSERT(!(WTF::kSuperPageSize % WTF::kPartitionPageSize), ok_super_page_multiple);
44 // Four system pages gives us room to hack out a still-guard-paged piece
45 // of metadata in the middle of a guard partition page.
46 COMPILE_ASSERT(WTF::kSystemPageSize * 4 <= WTF::kPartitionPageSize, ok_partition_page_size);
47 COMPILE_ASSERT(!(WTF::kPartitionPageSize % WTF::kSystemPageSize), ok_partition_page_multiple);
48 COMPILE_ASSERT(sizeof(WTF::PartitionPage) <= WTF::kPageMetadataSize, PartitionPage_not_too_big);
49 COMPILE_ASSERT(sizeof(WTF::PartitionBucket) <= WTF::kPageMetadataSize, PartitionBucket_not_too_big);
50 COMPILE_ASSERT(sizeof(WTF::PartitionSuperPageExtentEntry) <= WTF::kPageMetadataSize, PartitionSuperPageExtentEntry_not_too_big);
51 COMPILE_ASSERT(WTF::kPageMetadataSize * WTF::kNumPartitionPagesPerSuperPage <= WTF::kSystemPageSize, page_metadata_fits_in_hole);
52 // Check that some of our zanier calculations worked out as expected.
53 COMPILE_ASSERT(WTF::kGenericSmallestBucket == 8, generic_smallest_bucket);
54 COMPILE_ASSERT(WTF::kGenericMaxBucketed == 983040, generic_max_bucketed);
55
56 namespace WTF {
57
58 int PartitionRootBase::gInitializedLock = 0;
59 bool PartitionRootBase::gInitialized = false;
60 PartitionPage PartitionRootBase::gSeedPage;
61 PartitionBucket PartitionRootBase::gPagedBucket;
62
partitionBucketNumSystemPages(size_t size)63 static size_t partitionBucketNumSystemPages(size_t size)
64 {
65 // This works out reasonably for the current bucket sizes of the generic
66 // allocator, and the current values of partition page size and constants.
67 // Specifically, we have enough room to always pack the slots perfectly into
68 // some number of system pages. The only waste is the waste associated with
69 // unfaulted pages (i.e. wasted address space).
70 // TODO: we end up using a lot of system pages for very small sizes. For
71 // example, we'll use 12 system pages for slot size 24. The slot size is
72 // so small that the waste would be tiny with just 4, or 1, system pages.
73 // Later, we can investigate whether there are anti-fragmentation benefits
74 // to using fewer system pages.
75 double bestWasteRatio = 1.0f;
76 size_t bestPages = 0;
77 if (size > kMaxSystemPagesPerSlotSpan * kSystemPageSize) {
78 ASSERT(!(size % kSystemPageSize));
79 return size / kSystemPageSize;
80 }
81 ASSERT(size <= kMaxSystemPagesPerSlotSpan * kSystemPageSize);
82 for (size_t i = kNumSystemPagesPerPartitionPage - 1; i <= kMaxSystemPagesPerSlotSpan; ++i) {
83 size_t pageSize = kSystemPageSize * i;
84 size_t numSlots = pageSize / size;
85 size_t waste = pageSize - (numSlots * size);
86 // Leaving a page unfaulted is not free; the page will occupy an empty page table entry.
87 // Make a simple attempt to account for that.
88 size_t numRemainderPages = i & (kNumSystemPagesPerPartitionPage - 1);
89 size_t numUnfaultedPages = numRemainderPages ? (kNumSystemPagesPerPartitionPage - numRemainderPages) : 0;
90 waste += sizeof(void*) * numUnfaultedPages;
91 double wasteRatio = (double) waste / (double) pageSize;
92 if (wasteRatio < bestWasteRatio) {
93 bestWasteRatio = wasteRatio;
94 bestPages = i;
95 }
96 }
97 ASSERT(bestPages > 0);
98 return bestPages;
99 }
100
parititonAllocBaseInit(PartitionRootBase * root)101 static void parititonAllocBaseInit(PartitionRootBase* root)
102 {
103 ASSERT(!root->initialized);
104
105 spinLockLock(&PartitionRootBase::gInitializedLock);
106 if (!PartitionRootBase::gInitialized) {
107 PartitionRootBase::gInitialized = true;
108 // We mark the seed page as free to make sure it is skipped by our
109 // logic to find a new active page.
110 PartitionRootBase::gPagedBucket.activePagesHead = &PartitionRootGeneric::gSeedPage;
111 }
112 spinLockUnlock(&PartitionRootBase::gInitializedLock);
113
114 root->initialized = true;
115 root->totalSizeOfCommittedPages = 0;
116 root->totalSizeOfSuperPages = 0;
117 root->nextSuperPage = 0;
118 root->nextPartitionPage = 0;
119 root->nextPartitionPageEnd = 0;
120 root->firstExtent = 0;
121 root->currentExtent = 0;
122
123 memset(&root->globalEmptyPageRing, '\0', sizeof(root->globalEmptyPageRing));
124 root->globalEmptyPageRingIndex = 0;
125
126 // This is a "magic" value so we can test if a root pointer is valid.
127 root->invertedSelf = ~reinterpret_cast<uintptr_t>(root);
128 }
129
partitionBucketInitBase(PartitionBucket * bucket,PartitionRootBase * root)130 static void partitionBucketInitBase(PartitionBucket* bucket, PartitionRootBase* root)
131 {
132 bucket->activePagesHead = &PartitionRootGeneric::gSeedPage;
133 bucket->freePagesHead = 0;
134 bucket->numFullPages = 0;
135 bucket->numSystemPagesPerSlotSpan = partitionBucketNumSystemPages(bucket->slotSize);
136 }
137
partitionAllocInit(PartitionRoot * root,size_t numBuckets,size_t maxAllocation)138 void partitionAllocInit(PartitionRoot* root, size_t numBuckets, size_t maxAllocation)
139 {
140 parititonAllocBaseInit(root);
141
142 root->numBuckets = numBuckets;
143 root->maxAllocation = maxAllocation;
144 size_t i;
145 for (i = 0; i < root->numBuckets; ++i) {
146 PartitionBucket* bucket = &root->buckets()[i];
147 if (!i)
148 bucket->slotSize = kAllocationGranularity;
149 else
150 bucket->slotSize = i << kBucketShift;
151 partitionBucketInitBase(bucket, root);
152 }
153 }
154
partitionAllocGenericInit(PartitionRootGeneric * root)155 void partitionAllocGenericInit(PartitionRootGeneric* root)
156 {
157 parititonAllocBaseInit(root);
158
159 root->lock = 0;
160
161 // Precalculate some shift and mask constants used in the hot path.
162 // Example: malloc(41) == 101001 binary.
163 // Order is 6 (1 << 6-1)==32 is highest bit set.
164 // orderIndex is the next three MSB == 010 == 2.
165 // subOrderIndexMask is a mask for the remaining bits == 11 (masking to 01 for the subOrderIndex).
166 size_t order;
167 for (order = 0; order <= kBitsPerSizet; ++order) {
168 size_t orderIndexShift;
169 if (order < kGenericNumBucketsPerOrderBits + 1)
170 orderIndexShift = 0;
171 else
172 orderIndexShift = order - (kGenericNumBucketsPerOrderBits + 1);
173 root->orderIndexShifts[order] = orderIndexShift;
174 size_t subOrderIndexMask;
175 if (order == kBitsPerSizet) {
176 // This avoids invoking undefined behavior for an excessive shift.
177 subOrderIndexMask = static_cast<size_t>(-1) >> (kGenericNumBucketsPerOrderBits + 1);
178 } else {
179 subOrderIndexMask = ((1 << order) - 1) >> (kGenericNumBucketsPerOrderBits + 1);
180 }
181 root->orderSubIndexMasks[order] = subOrderIndexMask;
182 }
183
184 // Set up the actual usable buckets first.
185 // Note that typical values (i.e. min allocation size of 8) will result in
186 // invalid buckets (size==9 etc. or more generally, size is not a multiple
187 // of the smallest allocation granularity).
188 // We avoid them in the bucket lookup map, but we tolerate them to keep the
189 // code simpler and the structures more generic.
190 size_t i, j;
191 size_t currentSize = kGenericSmallestBucket;
192 size_t currentIncrement = kGenericSmallestBucket >> kGenericNumBucketsPerOrderBits;
193 PartitionBucket* bucket = &root->buckets[0];
194 for (i = 0; i < kGenericNumBucketedOrders; ++i) {
195 for (j = 0; j < kGenericNumBucketsPerOrder; ++j) {
196 bucket->slotSize = currentSize;
197 partitionBucketInitBase(bucket, root);
198 // Disable invalid buckets so that touching them faults.
199 if (currentSize % kGenericSmallestBucket)
200 bucket->activePagesHead = 0;
201 currentSize += currentIncrement;
202 ++bucket;
203 }
204 currentIncrement <<= 1;
205 }
206 ASSERT(currentSize == 1 << kGenericMaxBucketedOrder);
207 ASSERT(bucket == &root->buckets[0] + (kGenericNumBucketedOrders * kGenericNumBucketsPerOrder));
208
209 // Then set up the fast size -> bucket lookup table.
210 bucket = &root->buckets[0];
211 PartitionBucket** bucketPtr = &root->bucketLookups[0];
212 for (order = 0; order <= kBitsPerSizet; ++order) {
213 for (j = 0; j < kGenericNumBucketsPerOrder; ++j) {
214 if (order < kGenericMinBucketedOrder) {
215 // Use the bucket of finest granularity for malloc(0) etc.
216 *bucketPtr++ = &root->buckets[0];
217 } else if (order > kGenericMaxBucketedOrder) {
218 *bucketPtr++ = &PartitionRootGeneric::gPagedBucket;
219 } else {
220 PartitionBucket* validBucket = bucket;
221 // Skip over invalid buckets.
222 while (validBucket->slotSize % kGenericSmallestBucket)
223 validBucket++;
224 *bucketPtr++ = validBucket;
225 bucket++;
226 }
227 }
228 }
229 ASSERT(bucket == &root->buckets[0] + (kGenericNumBucketedOrders * kGenericNumBucketsPerOrder));
230 ASSERT(bucketPtr == &root->bucketLookups[0] + ((kBitsPerSizet + 1) * kGenericNumBucketsPerOrder));
231 // And there's one last bucket lookup that will be hit for e.g. malloc(-1),
232 // which tries to overflow to a non-existant order.
233 *bucketPtr = &PartitionRootGeneric::gPagedBucket;
234 }
235
partitionAllocShutdownBucket(PartitionBucket * bucket)236 static bool partitionAllocShutdownBucket(PartitionBucket* bucket)
237 {
238 // Failure here indicates a memory leak.
239 bool noLeaks = !bucket->numFullPages;
240 PartitionPage* page = bucket->activePagesHead;
241 while (page) {
242 if (page->numAllocatedSlots)
243 noLeaks = false;
244 page = page->nextPage;
245 }
246
247 return noLeaks;
248 }
249
partitionAllocBaseShutdown(PartitionRootBase * root)250 static void partitionAllocBaseShutdown(PartitionRootBase* root)
251 {
252 ASSERT(root->initialized);
253 root->initialized = false;
254
255 // Now that we've examined all partition pages in all buckets, it's safe
256 // to free all our super pages. We first collect the super page pointers
257 // on the stack because some of them are themselves store in super pages.
258 char* superPages[kMaxPartitionSize / kSuperPageSize];
259 size_t numSuperPages = 0;
260 PartitionSuperPageExtentEntry* entry = root->firstExtent;
261 while (entry) {
262 char* superPage = entry->superPageBase;
263 while (superPage != entry->superPagesEnd) {
264 superPages[numSuperPages] = superPage;
265 numSuperPages++;
266 superPage += kSuperPageSize;
267 }
268 entry = entry->next;
269 }
270 ASSERT(numSuperPages == root->totalSizeOfSuperPages / kSuperPageSize);
271 for (size_t i = 0; i < numSuperPages; ++i)
272 freePages(superPages[i], kSuperPageSize);
273 }
274
partitionAllocShutdown(PartitionRoot * root)275 bool partitionAllocShutdown(PartitionRoot* root)
276 {
277 bool noLeaks = true;
278 size_t i;
279 for (i = 0; i < root->numBuckets; ++i) {
280 PartitionBucket* bucket = &root->buckets()[i];
281 if (!partitionAllocShutdownBucket(bucket))
282 noLeaks = false;
283 }
284
285 partitionAllocBaseShutdown(root);
286 return noLeaks;
287 }
288
partitionAllocGenericShutdown(PartitionRootGeneric * root)289 bool partitionAllocGenericShutdown(PartitionRootGeneric* root)
290 {
291 bool noLeaks = true;
292 size_t i;
293 for (i = 0; i < kGenericNumBucketedOrders * kGenericNumBucketsPerOrder; ++i) {
294 PartitionBucket* bucket = &root->buckets[i];
295 if (!partitionAllocShutdownBucket(bucket))
296 noLeaks = false;
297 }
298 partitionAllocBaseShutdown(root);
299 return noLeaks;
300 }
301
partitionOutOfMemory()302 static NEVER_INLINE void partitionOutOfMemory()
303 {
304 IMMEDIATE_CRASH();
305 }
306
partitionFull()307 static NEVER_INLINE void partitionFull()
308 {
309 IMMEDIATE_CRASH();
310 }
311
partitionDecommitSystemPages(PartitionRootBase * root,void * addr,size_t len)312 static ALWAYS_INLINE void partitionDecommitSystemPages(PartitionRootBase* root, void* addr, size_t len)
313 {
314 decommitSystemPages(addr, len);
315 ASSERT(root->totalSizeOfCommittedPages > len);
316 root->totalSizeOfCommittedPages -= len;
317 }
318
partitionRecommitSystemPages(PartitionRootBase * root,void * addr,size_t len)319 static ALWAYS_INLINE void partitionRecommitSystemPages(PartitionRootBase* root, void* addr, size_t len)
320 {
321 recommitSystemPages(addr, len);
322 root->totalSizeOfCommittedPages += len;
323 }
324
partitionAllocPartitionPages(PartitionRootBase * root,int flags,size_t numPartitionPages)325 static ALWAYS_INLINE void* partitionAllocPartitionPages(PartitionRootBase* root, int flags, size_t numPartitionPages)
326 {
327 ASSERT(!(reinterpret_cast<uintptr_t>(root->nextPartitionPage) % kPartitionPageSize));
328 ASSERT(!(reinterpret_cast<uintptr_t>(root->nextPartitionPageEnd) % kPartitionPageSize));
329 RELEASE_ASSERT(numPartitionPages <= kNumPartitionPagesPerSuperPage);
330 size_t totalSize = kPartitionPageSize * numPartitionPages;
331 root->totalSizeOfCommittedPages += totalSize;
332 size_t numPartitionPagesLeft = (root->nextPartitionPageEnd - root->nextPartitionPage) >> kPartitionPageShift;
333 if (LIKELY(numPartitionPagesLeft >= numPartitionPages)) {
334 // In this case, we can still hand out pages from the current super page
335 // allocation.
336 char* ret = root->nextPartitionPage;
337 root->nextPartitionPage += totalSize;
338 return ret;
339 }
340
341 // Need a new super page.
342 root->totalSizeOfSuperPages += kSuperPageSize;
343 if (root->totalSizeOfSuperPages > kMaxPartitionSize)
344 partitionFull();
345 char* requestedAddress = root->nextSuperPage;
346 char* superPage = reinterpret_cast<char*>(allocPages(requestedAddress, kSuperPageSize, kSuperPageSize));
347 if (UNLIKELY(!superPage)) {
348 if (flags & PartitionAllocReturnNull)
349 return 0;
350 partitionOutOfMemory();
351 }
352 root->nextSuperPage = superPage + kSuperPageSize;
353 char* ret = superPage + kPartitionPageSize;
354 root->nextPartitionPage = ret + totalSize;
355 root->nextPartitionPageEnd = root->nextSuperPage - kPartitionPageSize;
356 // Make the first partition page in the super page a guard page, but leave a
357 // hole in the middle.
358 // This is where we put page metadata and also a tiny amount of extent
359 // metadata.
360 setSystemPagesInaccessible(superPage, kSystemPageSize);
361 setSystemPagesInaccessible(superPage + (kSystemPageSize * 2), kPartitionPageSize - (kSystemPageSize * 2));
362 // Also make the last partition page a guard page.
363 setSystemPagesInaccessible(superPage + (kSuperPageSize - kPartitionPageSize), kPartitionPageSize);
364
365 // If we were after a specific address, but didn't get it, assume that
366 // the system chose a lousy address and re-randomize the next
367 // allocation.
368 if (requestedAddress && requestedAddress != superPage)
369 root->nextSuperPage = 0;
370
371 // We allocated a new super page so update super page metadata.
372 // First check if this is a new extent or not.
373 PartitionSuperPageExtentEntry* latestExtent = reinterpret_cast<PartitionSuperPageExtentEntry*>(partitionSuperPageToMetadataArea(superPage));
374 PartitionSuperPageExtentEntry* currentExtent = root->currentExtent;
375 bool isNewExtent = (superPage != requestedAddress);
376 if (UNLIKELY(isNewExtent)) {
377 latestExtent->next = 0;
378 if (UNLIKELY(!currentExtent)) {
379 root->firstExtent = latestExtent;
380 } else {
381 ASSERT(currentExtent->superPageBase);
382 currentExtent->next = latestExtent;
383 }
384 root->currentExtent = latestExtent;
385 currentExtent = latestExtent;
386 currentExtent->superPageBase = superPage;
387 currentExtent->superPagesEnd = superPage + kSuperPageSize;
388 } else {
389 // We allocated next to an existing extent so just nudge the size up a little.
390 currentExtent->superPagesEnd += kSuperPageSize;
391 ASSERT(ret >= currentExtent->superPageBase && ret < currentExtent->superPagesEnd);
392 }
393 // By storing the root in every extent metadata object, we have a fast way
394 // to go from a pointer within the partition to the root object.
395 latestExtent->root = root;
396
397 return ret;
398 }
399
partitionUnusePage(PartitionRootBase * root,PartitionPage * page)400 static ALWAYS_INLINE void partitionUnusePage(PartitionRootBase* root, PartitionPage* page)
401 {
402 ASSERT(page->bucket->numSystemPagesPerSlotSpan);
403 void* addr = partitionPageToPointer(page);
404 partitionDecommitSystemPages(root, addr, page->bucket->numSystemPagesPerSlotSpan * kSystemPageSize);
405 }
406
partitionBucketSlots(const PartitionBucket * bucket)407 static ALWAYS_INLINE size_t partitionBucketSlots(const PartitionBucket* bucket)
408 {
409 return (bucket->numSystemPagesPerSlotSpan * kSystemPageSize) / bucket->slotSize;
410 }
411
partitionBucketPartitionPages(const PartitionBucket * bucket)412 static ALWAYS_INLINE size_t partitionBucketPartitionPages(const PartitionBucket* bucket)
413 {
414 return (bucket->numSystemPagesPerSlotSpan + (kNumSystemPagesPerPartitionPage - 1)) / kNumSystemPagesPerPartitionPage;
415 }
416
partitionPageReset(PartitionPage * page,PartitionBucket * bucket)417 static ALWAYS_INLINE void partitionPageReset(PartitionPage* page, PartitionBucket* bucket)
418 {
419 ASSERT(page != &PartitionRootGeneric::gSeedPage);
420 page->numAllocatedSlots = 0;
421 page->numUnprovisionedSlots = partitionBucketSlots(bucket);
422 ASSERT(page->numUnprovisionedSlots);
423 page->bucket = bucket;
424 page->nextPage = 0;
425 // NULLing the freelist is not strictly necessary but it makes an ASSERT in partitionPageFillFreelist simpler.
426 page->freelistHead = 0;
427 page->pageOffset = 0;
428 page->freeCacheIndex = -1;
429 size_t numPartitionPages = partitionBucketPartitionPages(bucket);
430 size_t i;
431 char* pageCharPtr = reinterpret_cast<char*>(page);
432 for (i = 1; i < numPartitionPages; ++i) {
433 pageCharPtr += kPageMetadataSize;
434 PartitionPage* secondaryPage = reinterpret_cast<PartitionPage*>(pageCharPtr);
435 secondaryPage->pageOffset = i;
436 }
437 }
438
partitionPageAllocAndFillFreelist(PartitionPage * page)439 static ALWAYS_INLINE char* partitionPageAllocAndFillFreelist(PartitionPage* page)
440 {
441 ASSERT(page != &PartitionRootGeneric::gSeedPage);
442 size_t numSlots = page->numUnprovisionedSlots;
443 ASSERT(numSlots);
444 PartitionBucket* bucket = page->bucket;
445 // We should only get here when _every_ slot is either used or unprovisioned.
446 // (The third state is "on the freelist". If we have a non-empty freelist, we should not get here.)
447 ASSERT(numSlots + page->numAllocatedSlots == partitionBucketSlots(bucket));
448 // Similarly, make explicitly sure that the freelist is empty.
449 ASSERT(!page->freelistHead);
450 ASSERT(page->numAllocatedSlots >= 0);
451
452 size_t size = bucket->slotSize;
453 char* base = reinterpret_cast<char*>(partitionPageToPointer(page));
454 char* returnObject = base + (size * page->numAllocatedSlots);
455 char* firstFreelistPointer = returnObject + size;
456 char* firstFreelistPointerExtent = firstFreelistPointer + sizeof(PartitionFreelistEntry*);
457 // Our goal is to fault as few system pages as possible. We calculate the
458 // page containing the "end" of the returned slot, and then allow freelist
459 // pointers to be written up to the end of that page.
460 char* subPageLimit = reinterpret_cast<char*>((reinterpret_cast<uintptr_t>(firstFreelistPointer) + kSystemPageOffsetMask) & kSystemPageBaseMask);
461 char* slotsLimit = returnObject + (size * page->numUnprovisionedSlots);
462 char* freelistLimit = subPageLimit;
463 if (UNLIKELY(slotsLimit < freelistLimit))
464 freelistLimit = slotsLimit;
465
466 size_t numNewFreelistEntries = 0;
467 if (LIKELY(firstFreelistPointerExtent <= freelistLimit)) {
468 // Only consider used space in the slot span. If we consider wasted
469 // space, we may get an off-by-one when a freelist pointer fits in the
470 // wasted space, but a slot does not.
471 // We know we can fit at least one freelist pointer.
472 numNewFreelistEntries = 1;
473 // Any further entries require space for the whole slot span.
474 numNewFreelistEntries += (freelistLimit - firstFreelistPointerExtent) / size;
475 }
476
477 // We always return an object slot -- that's the +1 below.
478 // We do not neccessarily create any new freelist entries, because we cross sub page boundaries frequently for large bucket sizes.
479 ASSERT(numNewFreelistEntries + 1 <= numSlots);
480 numSlots -= (numNewFreelistEntries + 1);
481 page->numUnprovisionedSlots = numSlots;
482 page->numAllocatedSlots++;
483
484 if (LIKELY(numNewFreelistEntries)) {
485 char* freelistPointer = firstFreelistPointer;
486 PartitionFreelistEntry* entry = reinterpret_cast<PartitionFreelistEntry*>(freelistPointer);
487 page->freelistHead = entry;
488 while (--numNewFreelistEntries) {
489 freelistPointer += size;
490 PartitionFreelistEntry* nextEntry = reinterpret_cast<PartitionFreelistEntry*>(freelistPointer);
491 entry->next = partitionFreelistMask(nextEntry);
492 entry = nextEntry;
493 }
494 entry->next = partitionFreelistMask(0);
495 } else {
496 page->freelistHead = 0;
497 }
498 return returnObject;
499 }
500
501 // This helper function scans the active page list for a suitable new active
502 // page, starting at the passed in page.
503 // When it finds a suitable new active page (one that has free slots), it is
504 // set as the new active page and true is returned. If there is no suitable new
505 // active page, false is returned and the current active page is set to null.
506 // As potential pages are scanned, they are tidied up according to their state.
507 // Freed pages are swept on to the free page list and full pages are unlinked
508 // from any list.
partitionSetNewActivePage(PartitionPage * page)509 static ALWAYS_INLINE bool partitionSetNewActivePage(PartitionPage* page)
510 {
511 if (page == &PartitionRootBase::gSeedPage) {
512 ASSERT(!page->nextPage);
513 return false;
514 }
515
516 PartitionPage* nextPage = 0;
517 PartitionBucket* bucket = page->bucket;
518
519 for (; page; page = nextPage) {
520 nextPage = page->nextPage;
521 ASSERT(page->bucket == bucket);
522 ASSERT(page != bucket->freePagesHead);
523 ASSERT(!bucket->freePagesHead || page != bucket->freePagesHead->nextPage);
524
525 // Page is usable if it has something on the freelist, or unprovisioned
526 // slots that can be turned into a freelist.
527 if (LIKELY(page->freelistHead != 0) || LIKELY(page->numUnprovisionedSlots)) {
528 bucket->activePagesHead = page;
529 return true;
530 }
531
532 ASSERT(page->numAllocatedSlots >= 0);
533 if (LIKELY(page->numAllocatedSlots == 0)) {
534 ASSERT(page->freeCacheIndex == -1);
535 // We hit a free page, so shepherd it on to the free page list.
536 page->nextPage = bucket->freePagesHead;
537 bucket->freePagesHead = page;
538 } else {
539 // If we get here, we found a full page. Skip over it too, and also
540 // tag it as full (via a negative value). We need it tagged so that
541 // free'ing can tell, and move it back into the active page list.
542 ASSERT(page->numAllocatedSlots == static_cast<int>(partitionBucketSlots(bucket)));
543 page->numAllocatedSlots = -page->numAllocatedSlots;
544 ++bucket->numFullPages;
545 // numFullPages is a uint16_t for efficient packing so guard against
546 // overflow to be safe.
547 RELEASE_ASSERT(bucket->numFullPages);
548 // Not necessary but might help stop accidents.
549 page->nextPage = 0;
550 }
551 }
552
553 bucket->activePagesHead = 0;
554 return false;
555 }
556
557 struct PartitionDirectMapExtent {
558 size_t mapSize; // Mapped size, not including guard pages and meta-data.
559 };
560
partitionPageToDirectMapExtent(PartitionPage * page)561 static ALWAYS_INLINE PartitionDirectMapExtent* partitionPageToDirectMapExtent(PartitionPage* page)
562 {
563 ASSERT(partitionBucketIsDirectMapped(page->bucket));
564 return reinterpret_cast<PartitionDirectMapExtent*>(reinterpret_cast<char*>(page) + 2 * kPageMetadataSize);
565 }
566
partitionDirectMap(PartitionRootBase * root,int flags,size_t size)567 static ALWAYS_INLINE void* partitionDirectMap(PartitionRootBase* root, int flags, size_t size)
568 {
569 size = partitionDirectMapSize(size);
570
571 // Because we need to fake looking like a super page, We need to allocate
572 // a bunch of system pages more than "size":
573 // - The first few system pages are the partition page in which the super
574 // page metadata is stored. We fault just one system page out of a partition
575 // page sized clump.
576 // - We add a trailing guard page.
577 size_t mapSize = size + kPartitionPageSize + kSystemPageSize;
578 // Round up to the allocation granularity.
579 mapSize += kPageAllocationGranularityOffsetMask;
580 mapSize &= kPageAllocationGranularityBaseMask;
581
582 // TODO: we may want to let the operating system place these allocations
583 // where it pleases. On 32-bit, this might limit address space
584 // fragmentation and on 64-bit, this might have useful savings for TLB
585 // and page table overhead.
586 // TODO: if upsizing realloc()s are common on large sizes, we could
587 // consider over-allocating address space on 64-bit, "just in case".
588 // TODO: consider pre-populating page tables (e.g. MAP_POPULATE on Linux,
589 // MADV_WILLNEED on POSIX).
590 // TODO: these pages will be zero-filled. Consider internalizing an
591 // allocZeroed() API so we can avoid a memset() entirely in this case.
592 char* ptr = reinterpret_cast<char*>(allocPages(0, mapSize, kSuperPageSize));
593 if (!ptr) {
594 if (flags & PartitionAllocReturnNull)
595 return 0;
596 partitionOutOfMemory();
597 }
598 char* ret = ptr + kPartitionPageSize;
599 // TODO: due to all the guard paging, this arrangement creates 4 mappings.
600 // We could get it down to three by using read-only for the metadata page,
601 // or perhaps two by leaving out the trailing guard page on 64-bit.
602 setSystemPagesInaccessible(ptr, kSystemPageSize);
603 setSystemPagesInaccessible(ptr + (kSystemPageSize * 2), kPartitionPageSize - (kSystemPageSize * 2));
604 setSystemPagesInaccessible(ret + size, kSystemPageSize);
605
606 PartitionSuperPageExtentEntry* extent = reinterpret_cast<PartitionSuperPageExtentEntry*>(partitionSuperPageToMetadataArea(ptr));
607 extent->root = root;
608 PartitionPage* page = partitionPointerToPageNoAlignmentCheck(ret);
609 PartitionBucket* bucket = reinterpret_cast<PartitionBucket*>(reinterpret_cast<char*>(page) + kPageMetadataSize);
610 page->freelistHead = 0;
611 page->nextPage = 0;
612 page->bucket = bucket;
613 page->numAllocatedSlots = 1;
614 page->numUnprovisionedSlots = 0;
615 page->pageOffset = 0;
616 page->freeCacheIndex = 0;
617
618 bucket->activePagesHead = 0;
619 bucket->freePagesHead = 0;
620 bucket->slotSize = size;
621 bucket->numSystemPagesPerSlotSpan = 0;
622 bucket->numFullPages = 0;
623
624 PartitionDirectMapExtent* mapExtent = partitionPageToDirectMapExtent(page);
625 mapExtent->mapSize = mapSize - kPartitionPageSize - kSystemPageSize;
626
627 return ret;
628 }
629
partitionDirectUnmap(PartitionPage * page)630 static ALWAYS_INLINE void partitionDirectUnmap(PartitionPage* page)
631 {
632 size_t unmapSize = partitionPageToDirectMapExtent(page)->mapSize;
633
634 // Add on the size of the trailing guard page and preceeding partition
635 // page.
636 unmapSize += kPartitionPageSize + kSystemPageSize;
637
638 ASSERT(!(unmapSize & kPageAllocationGranularityOffsetMask));
639
640 char* ptr = reinterpret_cast<char*>(partitionPageToPointer(page));
641 // Account for the mapping starting a partition page before the actual
642 // allocation address.
643 ptr -= kPartitionPageSize;
644
645 freePages(ptr, unmapSize);
646 }
647
partitionAllocSlowPath(PartitionRootBase * root,int flags,size_t size,PartitionBucket * bucket)648 void* partitionAllocSlowPath(PartitionRootBase* root, int flags, size_t size, PartitionBucket* bucket)
649 {
650 // The slow path is called when the freelist is empty.
651 ASSERT(!bucket->activePagesHead->freelistHead);
652
653 // For the partitionAllocGeneric API, we have a bunch of buckets marked
654 // as special cases. We bounce them through to the slow path so that we
655 // can still have a blazing fast hot path due to lack of corner-case
656 // branches.
657 bool returnNull = flags & PartitionAllocReturnNull;
658 if (UNLIKELY(partitionBucketIsDirectMapped(bucket))) {
659 ASSERT(size > kGenericMaxBucketed);
660 ASSERT(bucket == &PartitionRootBase::gPagedBucket);
661 if (size > kGenericMaxDirectMapped) {
662 if (returnNull)
663 return 0;
664 RELEASE_ASSERT(false);
665 }
666 return partitionDirectMap(root, flags, size);
667 }
668
669 // First, look for a usable page in the existing active pages list.
670 // Change active page, accepting the current page as a candidate.
671 if (LIKELY(partitionSetNewActivePage(bucket->activePagesHead))) {
672 PartitionPage* newPage = bucket->activePagesHead;
673 if (LIKELY(newPage->freelistHead != 0)) {
674 PartitionFreelistEntry* ret = newPage->freelistHead;
675 newPage->freelistHead = partitionFreelistMask(ret->next);
676 newPage->numAllocatedSlots++;
677 return ret;
678 }
679 ASSERT(newPage->numUnprovisionedSlots);
680 return partitionPageAllocAndFillFreelist(newPage);
681 }
682
683 // Second, look in our list of freed but reserved pages.
684 PartitionPage* newPage = bucket->freePagesHead;
685 if (LIKELY(newPage != 0)) {
686 ASSERT(newPage != &PartitionRootGeneric::gSeedPage);
687 ASSERT(!newPage->freelistHead);
688 ASSERT(!newPage->numAllocatedSlots);
689 ASSERT(!newPage->numUnprovisionedSlots);
690 ASSERT(newPage->freeCacheIndex == -1);
691 bucket->freePagesHead = newPage->nextPage;
692 void* addr = partitionPageToPointer(newPage);
693 partitionRecommitSystemPages(root, addr, newPage->bucket->numSystemPagesPerSlotSpan * kSystemPageSize);
694 } else {
695 // Third. If we get here, we need a brand new page.
696 size_t numPartitionPages = partitionBucketPartitionPages(bucket);
697 void* rawNewPage = partitionAllocPartitionPages(root, flags, numPartitionPages);
698 if (UNLIKELY(!rawNewPage)) {
699 ASSERT(returnNull);
700 return 0;
701 }
702 // Skip the alignment check because it depends on page->bucket, which is not yet set.
703 newPage = partitionPointerToPageNoAlignmentCheck(rawNewPage);
704 }
705
706 partitionPageReset(newPage, bucket);
707 bucket->activePagesHead = newPage;
708 return partitionPageAllocAndFillFreelist(newPage);
709 }
710
partitionFreePage(PartitionRootBase * root,PartitionPage * page)711 static ALWAYS_INLINE void partitionFreePage(PartitionRootBase* root, PartitionPage* page)
712 {
713 ASSERT(page->freelistHead);
714 ASSERT(!page->numAllocatedSlots);
715 partitionUnusePage(root, page);
716 // We actually leave the freed page in the active list. We'll sweep it on
717 // to the free page list when we next walk the active page list. Pulling
718 // this trick enables us to use a singly-linked page list for all cases,
719 // which is critical in keeping the page metadata structure down to 32
720 // bytes in size.
721 page->freelistHead = 0;
722 page->numUnprovisionedSlots = 0;
723 }
724
partitionRegisterEmptyPage(PartitionPage * page)725 static ALWAYS_INLINE void partitionRegisterEmptyPage(PartitionPage* page)
726 {
727 PartitionRootBase* root = partitionPageToRoot(page);
728
729 // If the page is already registered as empty, give it another life.
730 if (page->freeCacheIndex != -1) {
731 ASSERT(page->freeCacheIndex >= 0);
732 ASSERT(static_cast<unsigned>(page->freeCacheIndex) < kMaxFreeableSpans);
733 ASSERT(root->globalEmptyPageRing[page->freeCacheIndex] == page);
734 root->globalEmptyPageRing[page->freeCacheIndex] = 0;
735 }
736
737 size_t currentIndex = root->globalEmptyPageRingIndex;
738 PartitionPage* pageToFree = root->globalEmptyPageRing[currentIndex];
739 // The page might well have been re-activated, filled up, etc. before we get
740 // around to looking at it here.
741 if (pageToFree) {
742 ASSERT(pageToFree != &PartitionRootBase::gSeedPage);
743 ASSERT(pageToFree->freeCacheIndex >= 0);
744 ASSERT(static_cast<unsigned>(pageToFree->freeCacheIndex) < kMaxFreeableSpans);
745 ASSERT(pageToFree == root->globalEmptyPageRing[pageToFree->freeCacheIndex]);
746 if (!pageToFree->numAllocatedSlots && pageToFree->freelistHead) {
747 // The page is still empty, and not freed, so _really_ free it.
748 partitionFreePage(root, pageToFree);
749 }
750 pageToFree->freeCacheIndex = -1;
751 }
752
753 // We put the empty slot span on our global list of "pages that were once
754 // empty". thus providing it a bit of breathing room to get re-used before
755 // we really free it. This improves performance, particularly on Mac OS X
756 // which has subpar memory management performance.
757 root->globalEmptyPageRing[currentIndex] = page;
758 page->freeCacheIndex = currentIndex;
759 ++currentIndex;
760 if (currentIndex == kMaxFreeableSpans)
761 currentIndex = 0;
762 root->globalEmptyPageRingIndex = currentIndex;
763 }
764
partitionFreeSlowPath(PartitionPage * page)765 void partitionFreeSlowPath(PartitionPage* page)
766 {
767 PartitionBucket* bucket = page->bucket;
768 ASSERT(page != &PartitionRootGeneric::gSeedPage);
769 ASSERT(bucket->activePagesHead != &PartitionRootGeneric::gSeedPage);
770 if (LIKELY(page->numAllocatedSlots == 0)) {
771 // Page became fully unused.
772 if (UNLIKELY(partitionBucketIsDirectMapped(bucket))) {
773 partitionDirectUnmap(page);
774 return;
775 }
776 // If it's the current active page, attempt to change it. We'd prefer to leave
777 // the page empty as a gentle force towards defragmentation.
778 if (LIKELY(page == bucket->activePagesHead) && page->nextPage) {
779 if (partitionSetNewActivePage(page->nextPage)) {
780 ASSERT(bucket->activePagesHead != page);
781 // Link the empty page back in after the new current page, to
782 // avoid losing a reference to it.
783 // TODO: consider walking the list to link the empty page after
784 // all non-empty pages?
785 PartitionPage* currentPage = bucket->activePagesHead;
786 page->nextPage = currentPage->nextPage;
787 currentPage->nextPage = page;
788 } else {
789 bucket->activePagesHead = page;
790 page->nextPage = 0;
791 }
792 }
793 partitionRegisterEmptyPage(page);
794 } else {
795 // Ensure that the page is full. That's the only valid case if we
796 // arrive here.
797 ASSERT(page->numAllocatedSlots < 0);
798 // A transition of numAllocatedSlots from 0 to -1 is not legal, and
799 // likely indicates a double-free.
800 RELEASE_ASSERT(page->numAllocatedSlots != -1);
801 page->numAllocatedSlots = -page->numAllocatedSlots - 2;
802 ASSERT(page->numAllocatedSlots == static_cast<int>(partitionBucketSlots(bucket) - 1));
803 // Fully used page became partially used. It must be put back on the
804 // non-full page list. Also make it the current page to increase the
805 // chances of it being filled up again. The old current page will be
806 // the next page.
807 page->nextPage = bucket->activePagesHead;
808 bucket->activePagesHead = page;
809 --bucket->numFullPages;
810 // Special case: for a partition page with just a single slot, it may
811 // now be empty and we want to run it through the empty logic.
812 if (UNLIKELY(page->numAllocatedSlots == 0))
813 partitionFreeSlowPath(page);
814 }
815 }
816
partitionReallocDirectMappedInPlace(PartitionRootGeneric * root,PartitionPage * page,size_t newSize)817 bool partitionReallocDirectMappedInPlace(PartitionRootGeneric* root, PartitionPage* page, size_t newSize)
818 {
819 ASSERT(partitionBucketIsDirectMapped(page->bucket));
820
821 newSize = partitionCookieSizeAdjustAdd(newSize);
822
823 // Note that the new size might be a bucketed size; this function is called
824 // whenever we're reallocating a direct mapped allocation.
825 newSize = partitionDirectMapSize(newSize);
826 if (newSize < kGenericMinDirectMappedDownsize)
827 return false;
828
829 // bucket->slotSize is the current size of the allocation.
830 size_t currentSize = page->bucket->slotSize;
831 if (newSize == currentSize)
832 return true;
833
834 char* charPtr = static_cast<char*>(partitionPageToPointer(page));
835
836 if (newSize < currentSize) {
837 size_t mapSize = partitionPageToDirectMapExtent(page)->mapSize;
838
839 // Don't reallocate in-place if new size is less than 80 % of the full
840 // map size, to avoid holding on to too much unused address space.
841 if ((newSize / kSystemPageSize) * 5 < (mapSize / kSystemPageSize) * 4)
842 return false;
843
844 // Shrink by decommitting unneeded pages and making them inaccessible.
845 size_t decommitSize = currentSize - newSize;
846 partitionDecommitSystemPages(root, charPtr + newSize, decommitSize);
847 setSystemPagesInaccessible(charPtr + newSize, decommitSize);
848 } else if (newSize <= partitionPageToDirectMapExtent(page)->mapSize) {
849 // Grow within the actually allocated memory. Just need to make the
850 // pages accessible again.
851 size_t recommitSize = newSize - currentSize;
852 setSystemPagesAccessible(charPtr + currentSize, recommitSize);
853 partitionRecommitSystemPages(root, charPtr + currentSize, recommitSize);
854
855 #if ENABLE(ASSERT)
856 memset(charPtr + currentSize, kUninitializedByte, recommitSize);
857 #endif
858 } else {
859 // We can't perform the realloc in-place.
860 // TODO: support this too when possible.
861 return false;
862 }
863
864 #if ENABLE(ASSERT)
865 // Write a new trailing cookie.
866 partitionCookieWriteValue(charPtr + newSize - kCookieSize);
867 #endif
868
869 page->bucket->slotSize = newSize;
870 return true;
871 }
872
partitionReallocGeneric(PartitionRootGeneric * root,void * ptr,size_t newSize)873 void* partitionReallocGeneric(PartitionRootGeneric* root, void* ptr, size_t newSize)
874 {
875 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
876 return realloc(ptr, newSize);
877 #else
878 if (UNLIKELY(!ptr))
879 return partitionAllocGeneric(root, newSize);
880 if (UNLIKELY(!newSize)) {
881 partitionFreeGeneric(root, ptr);
882 return 0;
883 }
884
885 RELEASE_ASSERT(newSize <= kGenericMaxDirectMapped);
886
887 ASSERT(partitionPointerIsValid(partitionCookieFreePointerAdjust(ptr)));
888
889 PartitionPage* page = partitionPointerToPage(partitionCookieFreePointerAdjust(ptr));
890
891 if (UNLIKELY(partitionBucketIsDirectMapped(page->bucket))) {
892 // We may be able to perform the realloc in place by changing the
893 // accessibility of memory pages and, if reducing the size, decommitting
894 // them.
895 if (partitionReallocDirectMappedInPlace(root, page, newSize))
896 return ptr;
897 }
898
899 size_t actualNewSize = partitionAllocActualSize(root, newSize);
900 size_t actualOldSize = partitionAllocGetSize(ptr);
901
902 // TODO: note that tcmalloc will "ignore" a downsizing realloc() unless the
903 // new size is a significant percentage smaller. We could do the same if we
904 // determine it is a win.
905 if (actualNewSize == actualOldSize) {
906 // Trying to allocate a block of size newSize would give us a block of
907 // the same size as the one we've already got, so no point in doing
908 // anything here.
909 return ptr;
910 }
911
912 // This realloc cannot be resized in-place. Sadness.
913 void* ret = partitionAllocGeneric(root, newSize);
914 size_t copySize = actualOldSize;
915 if (newSize < copySize)
916 copySize = newSize;
917
918 memcpy(ret, ptr, copySize);
919 partitionFreeGeneric(root, ptr);
920 return ret;
921 #endif
922 }
923
924 #ifndef NDEBUG
925
partitionDumpStats(const PartitionRoot & root)926 void partitionDumpStats(const PartitionRoot& root)
927 {
928 size_t i;
929 size_t totalLive = 0;
930 size_t totalResident = 0;
931 size_t totalFreeable = 0;
932 for (i = 0; i < root.numBuckets; ++i) {
933 const PartitionBucket& bucket = root.buckets()[i];
934 if (bucket.activePagesHead == &PartitionRootGeneric::gSeedPage && !bucket.freePagesHead && !bucket.numFullPages) {
935 // Empty bucket with no freelist or full pages. Skip reporting it.
936 continue;
937 }
938 size_t numFreePages = 0;
939 PartitionPage* freePages = bucket.freePagesHead;
940 while (freePages) {
941 ++numFreePages;
942 freePages = freePages->nextPage;
943 }
944 size_t bucketSlotSize = bucket.slotSize;
945 size_t bucketNumSlots = partitionBucketSlots(&bucket);
946 size_t bucketUsefulStorage = bucketSlotSize * bucketNumSlots;
947 size_t bucketPageSize = bucket.numSystemPagesPerSlotSpan * kSystemPageSize;
948 size_t bucketWaste = bucketPageSize - bucketUsefulStorage;
949 size_t numActiveBytes = bucket.numFullPages * bucketUsefulStorage;
950 size_t numResidentBytes = bucket.numFullPages * bucketPageSize;
951 size_t numFreeableBytes = 0;
952 size_t numActivePages = 0;
953 const PartitionPage* page = bucket.activePagesHead;
954 while (page) {
955 ASSERT(page != &PartitionRootGeneric::gSeedPage);
956 // A page may be on the active list but freed and not yet swept.
957 if (!page->freelistHead && !page->numUnprovisionedSlots && !page->numAllocatedSlots) {
958 ++numFreePages;
959 } else {
960 ++numActivePages;
961 numActiveBytes += (page->numAllocatedSlots * bucketSlotSize);
962 size_t pageBytesResident = (bucketNumSlots - page->numUnprovisionedSlots) * bucketSlotSize;
963 // Round up to system page size.
964 pageBytesResident = (pageBytesResident + kSystemPageOffsetMask) & kSystemPageBaseMask;
965 numResidentBytes += pageBytesResident;
966 if (!page->numAllocatedSlots)
967 numFreeableBytes += pageBytesResident;
968 }
969 page = page->nextPage;
970 }
971 totalLive += numActiveBytes;
972 totalResident += numResidentBytes;
973 totalFreeable += numFreeableBytes;
974 printf("bucket size %zu (pageSize %zu waste %zu): %zu alloc/%zu commit/%zu freeable bytes, %zu/%zu/%zu full/active/free pages\n", bucketSlotSize, bucketPageSize, bucketWaste, numActiveBytes, numResidentBytes, numFreeableBytes, static_cast<size_t>(bucket.numFullPages), numActivePages, numFreePages);
975 }
976 printf("total live: %zu bytes\n", totalLive);
977 printf("total resident: %zu bytes\n", totalResident);
978 printf("total freeable: %zu bytes\n", totalFreeable);
979 fflush(stdout);
980 }
981
982 #endif // !NDEBUG
983
984 } // namespace WTF
985
986