[PATCH] D74869: [scudo][standalone] Drain the start of a cache, not the end

[Kostya Kortchinsky via Phabricator via llvm-commits]

cryptoad created this revision.
Herald added projects: Sanitizers, LLVM.
Herald added subscribers: llvm-commits, Sanitizers.

When we add a pointer to a cache, we add it at the end. By draining the
end, we were effectively putting back into the central freelist what
was just put in the local cache.

This improves performances, with no impact on memory footprint.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D74869

Files:
  compiler-rt/lib/scudo/standalone/local_cache.h


Index: compiler-rt/lib/scudo/standalone/local_cache.h
===================================================================
--- compiler-rt/lib/scudo/standalone/local_cache.h
+++ compiler-rt/lib/scudo/standalone/local_cache.h
@@ -165,13 +165,14 @@
 
   NOINLINE void drain(PerClass *C, uptr ClassId) {
     const u32 Count = Min(C->MaxCount / 2, C->Count);
-    const uptr FirstIndexToDrain = C->Count - Count;
-    TransferBatch *B = createBatch(ClassId, C->Chunks[FirstIndexToDrain]);
+    TransferBatch *B = createBatch(ClassId, C->Chunks[0]);
     if (UNLIKELY(!B))
       reportOutOfMemory(
           SizeClassAllocator::getSizeByClassId(SizeClassMap::BatchClassId));
-    B->setFromArray(&C->Chunks[FirstIndexToDrain], Count);
+    B->setFromArray(&C->Chunks[0], Count);
     C->Count -= Count;
+    for (uptr I = 0; I < C->Count; I++)
+      C->Chunks[I] = C->Chunks[I + Count];
     Allocator->pushBatch(ClassId, B);
   }
 };


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