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Fix 0-sized cold allocations #625

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Merged
copybara-service merged 1 commit into from
Sep 1, 2026
+14 −25
Merged

Fix 0-sized cold allocations #625

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11 changes: 2 additions & 9 deletions tcmalloc/sizemap.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -290,15 +290,8 @@ bool SizeMap::Init(absl::Span<const SizeClassInfo> size_classes) {
memset(cold_sizes_, 0, sizeof(cold_sizes_));
cold_sizes_count_ = 0;

// Point all lookups in the first or second upper register of class_array_
// (allocations seeking cold memory, with hints for partition 0, i.e.,
// pointerless allocations) to the lower size classes. This gives us an
// easy fallback for sizes that are too small for moving to cold memory (due
// to intrusive span metadata).
std::copy(&class_array_[0], &class_array_[kClassArraySize],
&class_array_[kClassArraySize * kColdRegisterStride]);

for (int c = kColdClassesStart; c < kNumClasses; c++) {
next_size = 0;
for (int c = kColdClassesStart + 1; c < kNumClasses; c++) {
size_t max_size_in_class = class_to_size_[c];
if (max_size_in_class == 0) {
next_size = max_size_in_class + static_cast<size_t>(kAlignment);
Expand Down
28 changes: 12 additions & 16 deletions tcmalloc/testing/tcmalloc_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1317,13 +1317,12 @@ TYPED_TEST(HotColdTest, HotColdNew) {
void* ptr;
size_t size;
};
constexpr size_t kSmall = 2 << 10;
constexpr size_t kLarge = 1 << 20;

std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
uint8_t label = absl::Uniform<uint8_t>(rng, 0, 127);
label |= uint8_t{128};

Expand Down Expand Up @@ -1353,7 +1352,7 @@ TYPED_TEST(HotColdTest, HotColdNew) {
// Allocate some cold objects
ptrs.clear();
for (int i = 0; i < 1000; i++) {
size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
uint8_t label = absl::Uniform<uint8_t>(rng, 0, 127);
label &= ~uint8_t{128};

Expand Down Expand Up @@ -1395,7 +1394,6 @@ TYPED_TEST(HotColdTest, NothrowHotColdNew) {
if (!expectColdTags) {
GTEST_SKIP() << "Cold allocations not enabled";
}
constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1409,7 +1407,7 @@ TYPED_TEST(HotColdTest, NothrowHotColdNew) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);

void* ptr = ::operator new(sizeof(TypeParam) * 0 + size, std::nothrow,
Expand Down Expand Up @@ -1442,7 +1440,6 @@ TYPED_TEST(HotColdTest, AlignedNothrowHotColdNew) {
if (!expectColdTags) {
GTEST_SKIP() << "Cold allocations not enabled";
}
constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1457,7 +1454,7 @@ TYPED_TEST(HotColdTest, AlignedNothrowHotColdNew) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
const std::align_val_t alignment =
static_cast<std::align_val_t>(1 << absl::Uniform(rng, 0, 6));
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);
Expand Down Expand Up @@ -1493,7 +1490,6 @@ TYPED_TEST(HotColdTest, ArrayNothrowHotColdNew) {
if (!expectColdTags) {
GTEST_SKIP() << "Cold allocations not enabled";
}
constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1507,7 +1503,7 @@ TYPED_TEST(HotColdTest, ArrayNothrowHotColdNew) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);

void* ptr = ::operator new[](sizeof(TypeParam) * 0 + size, std::nothrow,
Expand Down Expand Up @@ -1540,7 +1536,6 @@ TYPED_TEST(HotColdTest, ArrayAlignedNothrowHotColdNew) {
if (!expectColdTags) {
GTEST_SKIP() << "Cold allocations not enabled";
}
constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1555,7 +1550,7 @@ TYPED_TEST(HotColdTest, ArrayAlignedNothrowHotColdNew) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
const std::align_val_t alignment =
static_cast<std::align_val_t>(1 << absl::Uniform(rng, 0, 6));
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);
Expand Down Expand Up @@ -1591,7 +1586,6 @@ TYPED_TEST(HotColdTest, SizeReturningHotColdNew) {
if (!expectColdTags) {
GTEST_SKIP() << "Cold allocations not enabled";
}
constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1606,7 +1600,7 @@ TYPED_TEST(HotColdTest, SizeReturningHotColdNew) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t requested = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t requested = absl::LogUniform<size_t>(rng, 0, kLarge);
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);

auto [ptr, actual] = __size_returning_new_hot_cold(
Expand All @@ -1624,7 +1618,10 @@ TYPED_TEST(HotColdTest, SizeReturningHotColdNew) {
std::optional<size_t> allocated_size =
MallocExtension::GetAllocatedSize(ptr);
ASSERT_THAT(allocated_size, testing::Ne(std::nullopt));
EXPECT_EQ(actual, *allocated_size);
// Sanitizers mis-handle 0-sized allocations.
if (!kSanitizerPresent || actual != 0) {
EXPECT_EQ(actual, *allocated_size);
}

ptrs.emplace_back(SizedPtr{ptr, requested, actual});
}
Expand Down Expand Up @@ -1657,7 +1654,6 @@ TYPED_TEST(HotColdTest, HotColdNewMinHotFlag) {
static_cast<tcmalloc::hot_cold_t>(10);
Parameters::set_min_hot_access_hint(kNonDefaultMinHotAccessHint);

constexpr size_t kSmall = 128 << 10;
constexpr size_t kLarge = 1 << 20;

absl::BitGen rng;
Expand All @@ -1671,7 +1667,7 @@ TYPED_TEST(HotColdTest, HotColdNewMinHotFlag) {
std::vector<SizedPtr> ptrs;
ptrs.reserve(1000);
for (int i = 0; i < 1000; i++) {
const size_t size = absl::LogUniform<size_t>(rng, kSmall, kLarge);
const size_t size = absl::LogUniform<size_t>(rng, 0, kLarge);
const uint8_t label = absl::Uniform<uint8_t>(rng, 0, 255);

void* ptr = ::operator new(sizeof(TypeParam) * 0 + size,
Expand Down
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