[compiler-rt] [scudo] Add primary option to enable/disable cache blocks. (PR #129794)

[Jordan R AW via llvm-commits]

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@@ -184,6 +179,148 @@ template <class SizeClassAllocator> struct SizeClassAllocatorLocalCache {
   }
 };
 
+template <class SizeClassAllocator> struct SizeClassAllocatorNoCache {
+  typedef typename SizeClassAllocator::SizeClassMap SizeClassMap;
+  typedef typename SizeClassAllocator::CompactPtrT CompactPtrT;
+
+  void init(GlobalStats *S, SizeClassAllocator *A) {
+    Stats.init();
+    if (LIKELY(S))
+      S->link(&Stats);
+    Allocator = A;
+    initAllocator();
+  }
+
+  void destroy(GlobalStats *S) {
+    if (LIKELY(S))
+      S->unlink(&Stats);
+  }
+
+  void *allocate(uptr ClassId) {
+    CompactPtrT CompactPtr;
+    uptr NumBlocksPopped = Allocator->popBlocks(this, ClassId, &CompactPtr, 1U);
+    if (NumBlocksPopped == 0)
+      return nullptr;
+    DCHECK_EQ(NumBlocksPopped, 1U);
+    const PerClass *C = &PerClassArray[ClassId];
+    Stats.add(StatAllocated, C->ClassSize);
+    Stats.sub(StatFree, C->ClassSize);
+    return Allocator->decompactPtr(ClassId, CompactPtr);
+  }
+
+  bool deallocate(uptr ClassId, void *P) {
+    CHECK_LT(ClassId, NumClasses);
+
+    if (ClassId == BatchClassId)
+      return deallocateBatchClassBlock(P);
+
+    CompactPtrT CompactPtr =
+        Allocator->compactPtr(ClassId, reinterpret_cast<uptr>(P));
+    Allocator->pushBlocks(this, ClassId, &CompactPtr, 1U);
+    PerClass *C = &PerClassArray[ClassId];
+    Stats.sub(StatAllocated, C->ClassSize);
+    Stats.add(StatFree, C->ClassSize);
+
+    // The following adopts the same strategy of allocator draining as used
+    // in SizeClassAllocatorLocalCache so that use the same hint when doing
+    // a page release.
+    ++C->Count;
+    const bool SuggestDraining = C->Count == C->MaxCount;
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ajordanr-google wrote:

nit: should this be `>=`? There's a number of places where `Count` is incremented and it seems feasible that it could be already at `MaxCount` before the pre-increment.

I'm not going to be a stickler for `C->Count == 0`, as everywhere I've checked there doesn't seem to be a way for that to be less than zero, but it's harder to verify for increments.

https://github.com/llvm/llvm-project/pull/129794