[scudo] Remove unused field in BatchGroup (#109322)

Also fix the logic while determining the size of BatchClass and update
some legacy comments.

Author: ChiaHungDuan

compiler-rt/lib/scudo/standalone/allocator_common.h

@@ -75,16 +75,13 @@ template <class SizeClassAllocator> struct BatchGroup {
   BatchGroup *Next;
   // The compact base address of each group
   uptr CompactPtrGroupBase;
-  // Cache value of SizeClassAllocatorLocalCache::getMaxCached()
-  u16 MaxCachedPerBatch;
-  // Number of blocks pushed into this group. This is an increment-only
-  // counter.
-  uptr PushedBlocks;
   // This is used to track how many bytes are not in-use since last time we
   // tried to release pages.
   uptr BytesInBGAtLastCheckpoint;
   // Blocks are managed by TransferBatch in a list.
   SinglyLinkedList<TransferBatch<SizeClassAllocator>> Batches;
+  // Cache value of SizeClassAllocatorLocalCache::getMaxCached()
+  u16 MaxCachedPerBatch;
 };
 
 } // namespace scudo

compiler-rt/lib/scudo/standalone/primary32.h

@@ -56,12 +56,9 @@ template <typename Config> class SizeClassAllocator32 {
   typedef TransferBatch<ThisT> TransferBatchT;
   typedef BatchGroup<ThisT> BatchGroupT;
 
-  static_assert(sizeof(BatchGroupT) <= sizeof(TransferBatchT),
-                "BatchGroupT uses the same class size as TransferBatchT");
-
   static uptr getSizeByClassId(uptr ClassId) {
     return (ClassId == SizeClassMap::BatchClassId)
-               ? sizeof(TransferBatchT)
+               ? Max(sizeof(BatchGroupT), sizeof(TransferBatchT))
                : SizeClassMap::getSizeByClassId(ClassId);
   }
 
@@ -531,9 +528,6 @@ template <typename Config> class SizeClassAllocator32 {
       // BatchClass hasn't enabled memory group. Use `0` to indicate there's no
       // memory group here.
       BG->CompactPtrGroupBase = 0;
-      // `BG` is also the block of BatchClassId. Note that this is different
-      // from `CreateGroup` in `pushBlocksImpl`
-      BG->PushedBlocks = 1;
       BG->BytesInBGAtLastCheckpoint = 0;
       BG->MaxCachedPerBatch =
           CacheT::getMaxCached(getSizeByClassId(SizeClassMap::BatchClassId));
@@ -558,9 +552,6 @@ template <typename Config> class SizeClassAllocator32 {
       TB->add(
           compactPtr(SizeClassMap::BatchClassId, reinterpret_cast<uptr>(BG)));
       --Size;
-      DCHECK_EQ(BG->PushedBlocks, 1U);
-      // `TB` is also the block of BatchClassId.
-      BG->PushedBlocks += 1;
       BG->Batches.push_front(TB);
     }
 
@@ -587,8 +578,6 @@ template <typename Config> class SizeClassAllocator32 {
       CurBatch->appendFromArray(&Array[I], AppendSize);
       I += AppendSize;
     }
-
-    BG->PushedBlocks += Size;
   }
   // Push the blocks to their batch group. The layout will be like,
   //
@@ -624,7 +613,6 @@ template <typename Config> class SizeClassAllocator32 {
 
       BG->CompactPtrGroupBase = CompactPtrGroupBase;
       BG->Batches.push_front(TB);
-      BG->PushedBlocks = 0;
       BG->BytesInBGAtLastCheckpoint = 0;
       BG->MaxCachedPerBatch = TransferBatchT::MaxNumCached;
 
@@ -652,8 +640,6 @@ template <typename Config> class SizeClassAllocator32 {
         CurBatch->appendFromArray(&Array[I], AppendSize);
         I += AppendSize;
       }
-
-      BG->PushedBlocks += Size;
     };
 
     Sci->FreeListInfo.PushedBlocks += Size;

compiler-rt/lib/scudo/standalone/primary64.h

@@ -61,12 +61,12 @@ template <typename Config> class SizeClassAllocator64 {
   typedef TransferBatch<ThisT> TransferBatchT;
   typedef BatchGroup<ThisT> BatchGroupT;
 
-  static_assert(sizeof(BatchGroupT) <= sizeof(TransferBatchT),
-                "BatchGroupT uses the same class size as TransferBatchT");
-
+  // BachClass is used to store internal metadata so it needs to be at least as
+  // large as the largest data structure.
   static uptr getSizeByClassId(uptr ClassId) {
     return (ClassId == SizeClassMap::BatchClassId)
-               ? roundUp(sizeof(TransferBatchT), 1U << CompactPtrScale)
+               ? roundUp(Max(sizeof(TransferBatchT), sizeof(BatchGroupT)),
+                         1U << CompactPtrScale)
                : SizeClassMap::getSizeByClassId(ClassId);
   }
 
@@ -236,7 +236,7 @@ template <typename Config> class SizeClassAllocator64 {
     } else {
       while (true) {
         // When two threads compete for `Region->MMLock`, we only want one of
-        // them to call populateFreeListAndPopBatch(). To avoid both of them
+        // them to call populateFreeListAndPopBlocks(). To avoid both of them
         // doing that, always check the freelist before mapping new pages.
         ScopedLock ML(Region->MMLock);
         {
@@ -690,9 +690,6 @@ template <typename Config> class SizeClassAllocator64 {
       // BatchClass hasn't enabled memory group. Use `0` to indicate there's no
       // memory group here.
       BG->CompactPtrGroupBase = 0;
-      // `BG` is also the block of BatchClassId. Note that this is different
-      // from `CreateGroup` in `pushBlocksImpl`
-      BG->PushedBlocks = 1;
       BG->BytesInBGAtLastCheckpoint = 0;
       BG->MaxCachedPerBatch =
           CacheT::getMaxCached(getSizeByClassId(SizeClassMap::BatchClassId));
@@ -717,9 +714,6 @@ template <typename Config> class SizeClassAllocator64 {
       TB->add(
           compactPtr(SizeClassMap::BatchClassId, reinterpret_cast<uptr>(BG)));
       --Size;
-      DCHECK_EQ(BG->PushedBlocks, 1U);
-      // `TB` is also the block of BatchClassId.
-      BG->PushedBlocks += 1;
       BG->Batches.push_front(TB);
     }
 
@@ -746,8 +740,6 @@ template <typename Config> class SizeClassAllocator64 {
       CurBatch->appendFromArray(&Array[I], AppendSize);
       I += AppendSize;
     }
-
-    BG->PushedBlocks += Size;
   }
 
   // Push the blocks to their batch group. The layout will be like,
@@ -782,7 +774,6 @@ template <typename Config> class SizeClassAllocator64 {
 
       BG->CompactPtrGroupBase = CompactPtrGroupBase;
       BG->Batches.push_front(TB);
-      BG->PushedBlocks = 0;
       BG->BytesInBGAtLastCheckpoint = 0;
       BG->MaxCachedPerBatch = TransferBatchT::MaxNumCached;
 
@@ -810,8 +801,6 @@ template <typename Config> class SizeClassAllocator64 {
         CurBatch->appendFromArray(&Array[I], AppendSize);
         I += AppendSize;
       }
-
-      BG->PushedBlocks += Size;
     };
 
     Region->FreeListInfo.PushedBlocks += Size;
@@ -884,7 +873,7 @@ template <typename Config> class SizeClassAllocator64 {
     while (true) {
       // We only expect one thread doing the freelist refillment and other
       // threads will be waiting for either the completion of the
-      // `populateFreeListAndPopBatch()` or `pushBlocks()` called by other
+      // `populateFreeListAndPopBlocks()` or `pushBlocks()` called by other
       // threads.
       bool PopulateFreeList = false;
       {
@@ -922,7 +911,7 @@ template <typename Config> class SizeClassAllocator64 {
       // At here, there are two preconditions to be met before waiting,
       //   1. The freelist is empty.
       //   2. Region->isPopulatingFreeList == true, i.e, someone is still doing
-      //   `populateFreeListAndPopBatch()`.
+      //   `populateFreeListAndPopBlocks()`.
       //
       // Note that it has the chance that freelist is empty but
       // Region->isPopulatingFreeList == false because all the new populated
@@ -938,8 +927,8 @@ template <typename Config> class SizeClassAllocator64 {
 
       // Now the freelist is empty and someone's doing the refillment. We will
       // wait until anyone refills the freelist or someone finishes doing
-      // `populateFreeListAndPopBatch()`. The refillment can be done by
-      // `populateFreeListAndPopBatch()`, `pushBlocks()`,
+      // `populateFreeListAndPopBlocks()`. The refillment can be done by
+      // `populateFreeListAndPopBlocks()`, `pushBlocks()`,
       // `pushBatchClassBlocks()` and `mergeGroupsToReleaseBack()`.
       Region->FLLockCV.wait(Region->FLLock);
 
@@ -1119,8 +1108,8 @@ template <typename Config> class SizeClassAllocator64 {
 
     // Note that `PushedBlocks` and `PoppedBlocks` are supposed to only record
     // the requests from `PushBlocks` and `PopBatch` which are external
-    // interfaces. `populateFreeListAndPopBatch` is the internal interface so we
-    // should set the values back to avoid incorrectly setting the stats.
+    // interfaces. `populateFreeListAndPopBlocks` is the internal interface so
+    // we should set the values back to avoid incorrectly setting the stats.
     Region->FreeListInfo.PushedBlocks -= NumberOfBlocks;
 
     const uptr AllocatedUser = Size * NumberOfBlocks;
@@ -1689,7 +1678,6 @@ template <typename Config> class SizeClassAllocator64 {
       GroupsToRelease.pop_front();
 
       if (BG->CompactPtrGroupBase == Cur->CompactPtrGroupBase) {
-        BG->PushedBlocks += Cur->PushedBlocks;
         // We have updated `BatchGroup::BytesInBGAtLastCheckpoint` while
         // collecting the `GroupsToRelease`.
         BG->BytesInBGAtLastCheckpoint = Cur->BytesInBGAtLastCheckpoint;