perf: add per-class mesh trigger

Author: bpowers

src/CMakeLists.txt

@@ -39,6 +39,7 @@ set(unit_src
         testing/unit/concurrent_mesh_test.cc
         testing/unit/mesh_memory_test.cc
         testing/unit/mesh_test.cc
+        testing/unit/mesh_trigger_test.cc
         testing/unit/pending_list_test.cc
         testing/unit/rng_test.cc
         testing/unit/thread_exit_test.cc

src/global_heap.h

@@ -13,6 +13,7 @@
 
 #include "internal.h"
 #include "meshable_arena.h"
+#include "mesh_trigger.h"
 #include "mini_heap.h"
 
 #include "heaplayers.h"
@@ -127,7 +128,12 @@ class GlobalHeap : public MeshableArena<PageSize> {
     }
   };
 
-  GlobalHeap() : Super(), _maxObjectSize(SizeMap::ByteSizeForClass(kNumBins - 1)), _lastMesh{time::now()} {
+  GlobalHeap()
+      : Super(),
+        _maxObjectSize(SizeMap::ByteSizeForClass(kNumBins - 1)),
+        _meshEventBudget(initMeshEventBudget()),
+        _meshTrigger(_meshEventBudget),
+        _lastMesh{time::now()} {
   }
 
   inline void dumpStrings() const {
@@ -641,7 +647,7 @@ class GlobalHeap : public MeshableArena<PageSize> {
   // after call to meshLocked() completes src is a nullptr
   void ATTRIBUTE_NEVER_INLINE meshLocked(MiniHeapT *dst, MiniHeapT *&src);
 
-  inline void ATTRIBUTE_ALWAYS_INLINE maybeMesh() {
+  inline void ATTRIBUTE_ALWAYS_INLINE maybeMesh(int preferredSizeClass = -1) {
     if (!kMeshingEnabled) {
       return;
     }
@@ -655,32 +661,12 @@ class GlobalHeap : public MeshableArena<PageSize> {
       return;
     }
 
-    const auto now = time::now();
-    const auto lastMesh = _lastMesh.load(std::memory_order_acquire);
-    auto duration = chrono::duration_cast<chrono::milliseconds>(now - lastMesh);
-
-    if (likely(duration < meshPeriodMs)) {
+    size_t sizeClass = 0;
+    if (!_meshTrigger.popRequested(preferredSizeClass, sizeClass)) {
       return;
     }
 
-    AllLocksGuard allLocks(_miniheapLocks, _largeAllocLock, _arenaLock);
-
-    {
-      // ensure if two threads tried to grab the mesh lock at the same
-      // time, the second one bows out gracefully without meshing
-      // twice in a row.
-      const auto lockedNow = time::now();
-      const auto lockedLastMesh = _lastMesh.load(std::memory_order_relaxed);
-      auto duration = chrono::duration_cast<chrono::milliseconds>(lockedNow - lockedLastMesh);
-
-      if (unlikely(duration < meshPeriodMs)) {
-        return;
-      }
-    }
-
-    _lastMesh.store(now, std::memory_order_release);
-
-    meshAllSizeClassesLocked();
+    processMeshRequest(sizeClass);
   }
 
   inline bool okToProceed(void *ptr) const {
@@ -721,6 +707,8 @@ class GlobalHeap : public MeshableArena<PageSize> {
   }
 
 private:
+  static std::array<uint64_t, kNumBins> initMeshEventBudget();
+  void processMeshRequest(size_t sizeClass);
   // check for meshes in all size classes -- must be called LOCKED
   void meshAllSizeClassesLocked();
   // meshSizeClassLocked returns the number of merged sets found
@@ -731,6 +719,9 @@ class GlobalHeap : public MeshableArena<PageSize> {
   atomic_size_t _meshPeriod{kDefaultMeshPeriod};
   std::atomic<std::chrono::milliseconds> _meshPeriodMs{kMeshPeriodMs};
 
+  std::array<uint64_t, kNumBins> _meshEventBudget{};
+  internal::MeshTrigger<kNumBins> _meshTrigger{_meshEventBudget};
+
   atomic_size_t ATTRIBUTE_ALIGNED(CACHELINE_SIZE) _lastMeshEffective{0};
 
   // we want this on its own cacheline

src/global_heap_impl.h

@@ -36,6 +36,62 @@ MiniHeapID GetMiniHeapID(const MiniHeapT *mh) {
   return runtime<PageSize>().heap().miniheapIDFor(mh);
 }
 
+template <size_t PageSize>
+std::array<uint64_t, kNumBins> GlobalHeap<PageSize>::initMeshEventBudget() {
+  std::array<uint64_t, kNumBins> budgets{};
+  constexpr uint64_t minBudget = PageSize;
+  constexpr uint64_t maxBudget = static_cast<uint64_t>(PageSize) * 64ULL;
+  for (size_t i = 0; i < kNumBins; i++) {
+    const uint64_t objSize = static_cast<uint64_t>(SizeMap::ByteSizeForClass(static_cast<int32_t>(i)));
+    uint64_t budget = objSize * 32;
+    if (budget < minBudget) {
+      budget = minBudget;
+    } else if (budget > maxBudget) {
+      budget = maxBudget;
+    }
+    budgets[i] = budget;
+  }
+  return budgets;
+}
+
+template <size_t PageSize>
+struct MeshScratch {
+  MergeSetArray<PageSize> &mergeSets;
+  SplitArray<PageSize> &left;
+  SplitArray<PageSize> &right;
+};
+
+template <size_t PageSize>
+static MeshScratch<PageSize> getMeshScratch() {
+  static MergeSetArray<PageSize> *MergeSetsPtr = []() {
+    void *ptr =
+        mmap(nullptr, sizeof(MergeSetArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    hard_assert(ptr != MAP_FAILED);
+    return new (ptr) MergeSetArray<PageSize>();
+  }();
+  static MergeSetArray<PageSize> &MergeSets = *MergeSetsPtr;
+
+  static SplitArray<PageSize> *LeftPtr = []() {
+    void *ptr = mmap(nullptr, sizeof(SplitArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    hard_assert(ptr != MAP_FAILED);
+    return new (ptr) SplitArray<PageSize>();
+  }();
+  static SplitArray<PageSize> &Left = *LeftPtr;
+
+  static SplitArray<PageSize> *RightPtr = []() {
+    void *ptr = mmap(nullptr, sizeof(SplitArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    hard_assert(ptr != MAP_FAILED);
+    return new (ptr) SplitArray<PageSize>();
+  }();
+  static SplitArray<PageSize> &Right = *RightPtr;
+
+  d_assert((reinterpret_cast<uintptr_t>(&MergeSets) & (getPageSize() - 1)) == 0);
+  d_assert((reinterpret_cast<uintptr_t>(&Left) & (getPageSize() - 1)) == 0);
+  d_assert((reinterpret_cast<uintptr_t>(&Right) & (getPageSize() - 1)) == 0);
+
+  return {MergeSets, Left, Right};
+}
+
 template <size_t PageSize>
 void *GlobalHeap<PageSize>::malloc(size_t sz) {
 #ifndef NDEBUG
@@ -88,9 +144,14 @@ void GlobalHeap<PageSize>::freeFor(MiniHeapT *mh, void *ptr, size_t startEpoch)
 
   d_assert(mh->maxCount() > 1);
 
+  const size_t objectSize = mh->objectSize();
+  const size_t spanBytes = mh->spanSize();
+
   auto freelistId = mh->freelistId();
   auto isAttached = mh->isAttached();
   auto sizeClass = mh->sizeClass();
+  bool transitionedToPartial = false;
+  bool becameEmpty = false;
 
   // try to avoid storing to this cacheline; the branch is worth it to avoid
   // multi-threaded contention
@@ -151,6 +212,9 @@ void GlobalHeap<PageSize>::freeFor(MiniHeapT *mh, void *ptr, size_t startEpoch)
     isAttached = mh->isAttached();
 
     if (!isAttached && (remaining == 0 || freelistId == list::Full)) {
+      becameEmpty = remaining == 0;
+      transitionedToPartial = remaining > 0 && freelistId == list::Full;
+      shouldMesh = true;
       // this may free the miniheap -- we can't safely access it after
       // this point.
       postFreeLocked(mh, sizeClass, remaining);
@@ -173,6 +237,7 @@ void GlobalHeap<PageSize>::freeFor(MiniHeapT *mh, void *ptr, size_t startEpoch)
         // the exact crossing, the next free will catch it.
         if (isBelowPartialThreshold(remaining, mh->maxCount())) {
           tryPushPendingPartial(mh, sizeClass);
+          transitionedToPartial = true;
         }
         shouldMesh = true;
       } else {
@@ -238,21 +303,67 @@ void GlobalHeap<PageSize>::freeFor(MiniHeapT *mh, void *ptr, size_t startEpoch)
         remaining = mh->inUseCount();
         postFreeLocked(mh, sizeClass, remaining);
         // Note: flushBinLocked deferred to next mesh cycle (requires arena lock)
+        becameEmpty = true;
+        shouldMesh = true;
       }
     } else {
       shouldMesh = !isAttached;
     }
   }
 
-  if (shouldMesh) {
-    // Sample maybeMesh calls using pointer address bits to avoid overhead of
-    // calling clock_gettime on every free. Check ~1 in 4096 frees.
-    // Use bits 12-23 (above page offset, below typical allocation patterns).
-    constexpr uintptr_t kMeshSampleMask = 0xFFF000;
-    if (unlikely((reinterpret_cast<uintptr_t>(ptr) & kMeshSampleMask) == 0)) {
-      maybeMesh();
+  if (shouldMesh && !isAttached && sizeClass >= 0) {
+    size_t delta = objectSize;
+    if (transitionedToPartial || becameEmpty) {
+      delta += spanBytes;
+    }
+    _meshTrigger.add(static_cast<size_t>(sizeClass), delta);
+    maybeMesh(sizeClass);
+  }
+}
+
+template <size_t PageSize>
+void GlobalHeap<PageSize>::processMeshRequest(size_t sizeClass) {
+  d_assert(sizeClass < kNumBins);
+  auto scratch = getMeshScratch<PageSize>();
+  const uint64_t budget = _meshTrigger.adjustedBudget(sizeClass);
+
+  size_t meshCount = 0;
+  bool aboveThreshold = false;
+
+  {
+    // Lock ordering: size-class lock -> arena lock -> epoch lock
+    // This matches meshAllSizeClassesLocked (called via AllLocksGuard in mallctl)
+    lock_guard<mutex> sizeLock(_miniheapLocks[sizeClass]);
+    lock_guard<mutex> arenaLock(_arenaLock);
+
+    // if we have freed but not reset meshed mappings, this will reset
+    // them to the identity mapping, ensuring we don't blow past our VMA
+    // limit (which is why we set the force flag to true)
+    Super::scavenge(true);
+
+    if (Super::aboveMeshThreshold()) {
+      aboveThreshold = true;
+    } else {
+      // Acquire epoch lock last to match lock ordering in meshAllSizeClassesLocked
+      lock_guard<EpochLock> epochLock(_meshEpoch);
+
+      drainPendingPartialLocked(sizeClass);
+      flushBinLocked(sizeClass);
+      meshCount = meshSizeClassLocked(sizeClass, scratch.mergeSets, scratch.left, scratch.right);
+      madvise(&scratch.left, sizeof(scratch.left), MADV_DONTNEED);
+      madvise(&scratch.right, sizeof(scratch.right), MADV_DONTNEED);
+      madvise(&scratch.mergeSets, sizeof(scratch.mergeSets), MADV_DONTNEED);
+      Super::scavenge(true);
     }
   }
+
+  if (!aboveThreshold) {
+    _lastMeshEffective.store(meshCount > 0 ? 1 : 0, std::memory_order_release);
+    _stats.meshCount += meshCount;
+  }
+
+  _meshTrigger.onMeshComplete(sizeClass, meshCount > 0, budget);
+  _lastMesh.store(time::now(), std::memory_order_release);
 }
 
 template <size_t PageSize>
@@ -428,34 +539,7 @@ size_t GlobalHeap<PageSize>::meshSizeClassLocked(size_t sizeClass, MergeSetArray
 
 template <size_t PageSize>
 void GlobalHeap<PageSize>::meshAllSizeClassesLocked() {
-  static MergeSetArray<PageSize> *MergeSetsPtr = []() {
-    void *ptr =
-        mmap(nullptr, sizeof(MergeSetArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-    hard_assert(ptr != MAP_FAILED);
-    return new (ptr) MergeSetArray<PageSize>();
-  }();
-  static MergeSetArray<PageSize> &MergeSets = *MergeSetsPtr;
-  // static_assert(sizeof(MergeSets) == sizeof(void *) * 2 * 4096, "array too big");
-  d_assert((reinterpret_cast<uintptr_t>(&MergeSets) & (getPageSize() - 1)) == 0);
-
-  static SplitArray<PageSize> *LeftPtr = []() {
-    void *ptr = mmap(nullptr, sizeof(SplitArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-    hard_assert(ptr != MAP_FAILED);
-    return new (ptr) SplitArray<PageSize>();
-  }();
-  static SplitArray<PageSize> &Left = *LeftPtr;
-
-  static SplitArray<PageSize> *RightPtr = []() {
-    void *ptr = mmap(nullptr, sizeof(SplitArray<PageSize>), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-    hard_assert(ptr != MAP_FAILED);
-    return new (ptr) SplitArray<PageSize>();
-  }();
-  static SplitArray<PageSize> &Right = *RightPtr;
-
-  // static_assert(sizeof(Left) == sizeof(void *) * 16384, "array too big");
-  // static_assert(sizeof(Right) == sizeof(void *) * 16384, "array too big");
-  d_assert((reinterpret_cast<uintptr_t>(&Left) & (getPageSize() - 1)) == 0);
-  d_assert((reinterpret_cast<uintptr_t>(&Right) & (getPageSize() - 1)) == 0);
+  auto scratch = getMeshScratch<PageSize>();
 
   // if we have freed but not reset meshed mappings, this will reset
   // them to the identity mapping, ensuring we don't blow past our VMA
@@ -483,12 +567,12 @@ void GlobalHeap<PageSize>::meshAllSizeClassesLocked() {
   size_t totalMeshCount = 0;
 
   for (size_t sizeClass = 0; sizeClass < kNumBins; sizeClass++) {
-    totalMeshCount += meshSizeClassLocked(sizeClass, MergeSets, Left, Right);
+    totalMeshCount += meshSizeClassLocked(sizeClass, scratch.mergeSets, scratch.left, scratch.right);
   }
 
-  madvise(&Left, sizeof(Left), MADV_DONTNEED);
-  madvise(&Right, sizeof(Right), MADV_DONTNEED);
-  madvise(&MergeSets, sizeof(MergeSets), MADV_DONTNEED);
+  madvise(&scratch.left, sizeof(scratch.left), MADV_DONTNEED);
+  madvise(&scratch.right, sizeof(scratch.right), MADV_DONTNEED);
+  madvise(&scratch.mergeSets, sizeof(scratch.mergeSets), MADV_DONTNEED);
 
   _lastMeshEffective = totalMeshCount > 256;
   _stats.meshCount += totalMeshCount;