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Snapshot high water mark data for computing realized fragmentation.
This approximates "Adaptive Huge-Page Subrelease for Non-moving Memory
Allocators in Warehouse-Scale Computers"'s estimate of realized fragmentation
as T_{schedule} -> infinity. It captures memory going unused at a peak in
OS-visible demand due to metadata requirements and binpacking losses.
PiperOrigin-RevId: 439611199
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| // Copyright 2022 The TCMalloc Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // https://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| #include <string> | ||
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| #include "gmock/gmock.h" | ||
| #include "gtest/gtest.h" | ||
| #include "absl/random/random.h" | ||
| #include "absl/strings/numbers.h" | ||
| #include "tcmalloc/internal/linked_list.h" | ||
| #include "tcmalloc/testing/testutil.h" | ||
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| namespace tcmalloc { | ||
| namespace { | ||
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| using tcmalloc_internal::SLL_Pop; | ||
| using tcmalloc_internal::SLL_Push; | ||
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| struct PeakStats { | ||
| size_t backing; | ||
| size_t application; | ||
| }; | ||
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| PeakStats GetPeakStats() { | ||
| // TODO(ckennelly): Parse this with protobuf directly | ||
| PeakStats ret; | ||
| const std::string buf = GetStatsInPbTxt(); | ||
| constexpr absl::string_view backing_needle = "peak_backed: "; | ||
| constexpr absl::string_view application_needle = "peak_application_demand: "; | ||
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| auto parse = [](absl::string_view buf, absl::string_view needle) { | ||
| auto pos = buf.find(needle); | ||
| EXPECT_NE(pos, absl::string_view::npos); | ||
| pos += needle.size(); | ||
| auto stop = buf.find(' ', pos); | ||
| if (stop != absl::string_view::npos) { | ||
| stop -= pos; | ||
| } | ||
| size_t ret; | ||
| EXPECT_TRUE(absl::SimpleAtoi(buf.substr(pos, stop), &ret)) | ||
| << buf.substr(pos, stop); | ||
| return ret; | ||
| }; | ||
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| ret.backing = parse(buf, backing_needle); | ||
| ret.application = parse(buf, application_needle); | ||
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| return ret; | ||
| } | ||
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| TEST(RealizedFragmentation, Accuracy) { | ||
| #ifndef NDEBUG | ||
| GTEST_SKIP() << "Skipping test under debug build for performance"; | ||
| #endif | ||
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| const PeakStats starting = GetPeakStats(); | ||
| // We have allocated at least once up to this point. | ||
| ASSERT_GT(starting.backing, 0); | ||
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| // Since application data is sampled, allow wider error bars. | ||
| constexpr double kBackingTolerance = 0.20; | ||
| constexpr double kApplicationTolerance = 0.25; | ||
| absl::BitGen rng; | ||
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| // Allocate many 2MB allocations, as to trigger a new high water mark, then | ||
| // deallocate. | ||
| constexpr size_t kLargeTarget = 1 << 29; | ||
| constexpr size_t kLargeSize = 2 << 20; | ||
| void* large_list = nullptr; | ||
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| for (size_t total = 0; total < kLargeTarget; total += kLargeSize) { | ||
| SLL_Push(&large_list, ::operator new(kLargeSize)); | ||
| } | ||
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| const PeakStats peak0 = GetPeakStats(); | ||
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| EXPECT_NEAR(peak0.backing, starting.backing + kLargeTarget, | ||
| (starting.backing + kLargeTarget) * kBackingTolerance); | ||
| EXPECT_NEAR(peak0.application, starting.application + kLargeTarget, | ||
| (starting.application + kLargeTarget) * kApplicationTolerance); | ||
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| while (large_list != nullptr) { | ||
| void* object = SLL_Pop(&large_list); | ||
| sized_delete(object, kLargeSize); | ||
| } | ||
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| // Allocate many small alocations, as to trigger another high water mark. | ||
| // Deallocate half of these allocations, but fragmentation should remain high. | ||
| constexpr size_t kSmallTarget = kLargeTarget * 2; | ||
| constexpr size_t kSmallSize = 1024; | ||
| void* small_list_keep = nullptr; | ||
| int kept = 0; | ||
| void* small_list_free = nullptr; | ||
| int freed = 0; | ||
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| for (size_t total = 0; total < kSmallTarget; total += kSmallSize) { | ||
| void* object = ::operator new(kSmallSize); | ||
| if (absl::Bernoulli(rng, 0.5)) { | ||
| SLL_Push(&small_list_keep, object); | ||
| kept++; | ||
| } else { | ||
| SLL_Push(&small_list_free, object); | ||
| freed++; | ||
| } | ||
| } | ||
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| const PeakStats peak1 = GetPeakStats(); | ||
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| EXPECT_NEAR(peak1.backing, starting.backing + kSmallTarget, | ||
| (starting.backing + kSmallTarget) * kBackingTolerance); | ||
| EXPECT_NEAR(peak1.application, starting.application + kSmallTarget, | ||
| (starting.application + kSmallTarget) * kApplicationTolerance); | ||
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| while (small_list_free != nullptr) { | ||
| void* object = SLL_Pop(&small_list_free); | ||
| sized_delete(object, kSmallSize); | ||
| } | ||
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| // Allocate many 2MB allocations, as to trigger another high water mark. | ||
| // Fragmentation should continue to be high due to partial spans from the | ||
| // previous round. | ||
| for (size_t total = 0; total < 2 * kLargeTarget; total += kLargeSize) { | ||
| SLL_Push(&large_list, ::operator new(kLargeSize)); | ||
| } | ||
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| const PeakStats peak2 = GetPeakStats(); | ||
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| const double expected_backing = | ||
| starting.backing + kSmallTarget + 2 * kLargeTarget; | ||
| const double expected_application = | ||
| starting.backing + kSmallSize * kept + 2 * kLargeTarget; | ||
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| EXPECT_NEAR(peak2.backing, expected_backing, | ||
| expected_backing * kBackingTolerance); | ||
| EXPECT_NEAR(peak2.application, expected_application, | ||
| expected_application * kApplicationTolerance); | ||
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| while (large_list != nullptr) { | ||
| void* object = SLL_Pop(&large_list); | ||
| sized_delete(object, kLargeSize); | ||
| } | ||
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| while (small_list_keep != nullptr) { | ||
| void* object = SLL_Pop(&small_list_keep); | ||
| sized_delete(object, kSmallSize); | ||
| } | ||
| } | ||
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| } // namespace | ||
| } // namespace tcmalloc |